[６．３]　　　　　研究例

[６．３．１Ａ]       研究例（Ａ１）　　「ＫＡＩＳＴ」の研究　　　     （２０１３．１２．４）

[６．３．１Ａ．１]　　　　リチウム硫黄電池のシステム

（１）　リチウムイオンよりも長持ちする「リチウム硫黄二次電池」を開発。

（２）　従来よりエネルギー密度5倍以上向上…1000回の充放電にも容量維持。

（３）　「ＫＡＩＳＴ」(韓国科学技術院、カン・ソンモ総長)は「新素材工学科」の「キム・ドギョン教授」と
　　　 「ＥＥＷＳ」の「チェ・ジャンウク教授」が共同で、現在商用化されている
　　　 「リチウム・イオン電池」より寿命と「エネルギ密度」が向上した「リチウム硫黄二次電池」を
　　　　開発したと「２０１３年１２月３日」に発表した。

（４）　今回開発された「リチウム硫黄二次電池」は「単位重量」当りの「エネルギ密度」が
　　　　最大で「２１００Ｗｈ/ｋｇ」と、商用化されている「リチウム・イオン電池」
　　　　(最大３８７Ｗｈ/ｋｇ)の「５．４倍」に達する。
　　　　またこれまでに開発された「リチウム硫黄二次電池」とはちがい、「数百回」の充放電が可能。

（５）　研究チームは「ナノ電極材料合成技術」を活用して「厚さ７５ｎｍ(ナノメートル)」
　　　 「長さ１５μｍ(マイクロメートル)」の「硫黄ナノワイヤ」を垂直に整列して
　　　　電極材料を製造した。

（６）　　この「硫黄ナノワイヤ整列構造」は「１次元構造体」であり、電子の速い移動が
　　　　可能なため電極の伝導度が向上した。

（７）　　また「硫黄ナノワイヤ」の表面に均一に炭素をコーティングし「硫黄」と「電解液」が
　　　　　直接接触しないことから、充放電中に「硫黄」が溶けることを防止、
　　　　　「ＲＬＳＢ」のもつ寿命の短さという問題を解決した。

（８）　　これまでに開発されている「ＲＬＳＢ」用の「電極」は
　　　　最初は高い容量を示すものの充放電を繰り返すと容量が持続的に減少した。

（９）　　しかし今回開発された「電極」は速い放電速度(３分ごとに１回の充放電条件)で
　　　　「３００回」の充放電の後でも最初の容量の「９９．２％」を維持、
　　　　「１０００回」の充放電の後に「７０％以上」の容量を示した。

（１０）　研究チームは関連技術について「韓国国内特許」１件と「ＰＣＴ国際特許」１件を出願した。

（１１）　「キム・ドギョン教授」は
　　　　　「このリチウム硫黄電池は無人飛行機、電気自動車および再生エネルギー貯蔵装置などに必要な
　　　　　次世代高性能二次電池の実現を早めるのに役立つだろう。
　　　　　リチウム硫黄電池の問題だった寿命低下の解決方案を提示できた」
　　　　　と話している。

（１２）　研究結果はナノ素材分野の国際学術誌「Advanced Materials」に12月3日付で掲載された。

[６．３．１Ａ．２]　　　成果

（１）　成果を図１に示す。


   

　　　　　　　　　　　図１　　

(This figure is quoted from the document said above)
　　　　　

（２）　　「電流レート」は「２Ｃ」である。

（３）　　ほぼ実用のレベルに達している。

（４）　　「ＥＶ」の搭載して「試作車」を走らせてほしい。


[６．３．２Ａ]　　　　　研究例（２Ａ）   New lithium/sulfur battery doubles energy density of lithium-ion

                                            　　By Brian Dodson,    Lawrence Berkeley Lab,   December 1, 2013

[６．３．２Ａ．１]　　　「ＲＬＳＢ」のシステム

（１）　Batteries. We buy them at the store, use them up, and throw them away without much thought.

（２）　In reality, however, batteries are remarkably complex electrochemical devices that are continually evolving.

（３）　The latest example of this comes from the Lawrence Berkeley National Laboratory,
　　　　where researchers have invented an advanced lithium/sulfur (Li/S) cell that offers a unique combination
　　　　of energy storage, power, recharge speed, and survivability.

（４）　Lithium/sulfur rechargeable batteries offer a remarkably large capacity for energy storage,
　　　　mainly because two electrons are produced each time a molecule is processed through the battery's chemistry.

（５）　The voltage of a Li/S cell depends on the chemical entities in which electrical energy is ...

（６）　A basic Li/S cell consists of a lithium anode, a carbon-sulfur cathode, and an electrolyte
　　　　that permits lithium ions to pass.

（７）　The overall cell reaction during discharge converts lithium metal in the anode into Li2S
　　　　at the surface of the cathode.

（８）　The flow of two lithium ions from the anode to the cathode is then balanced
　　　　by the flow of two electrons between the battery contacts, delivering double the current
　　　　of a Li-ion battery
　　　　at a voltage between about 1.7 and 2.5 volts, depending on the state of charge of the cell.

（９）　　Lithium polysulfides are formed at intermediate charge levels, which affect the cell voltage
　　　　as indicated above.

（１０）　That's the good news. The bad news involves a host of materials problems associated
　　　　　with the basic Li/S chemistry and some side reactions.

（１１）　When the sulfur in the cathode absorbs lithium ions from the electrolyte, the Li2S has nearly
　　　　　double the volume of the original sulfur.

（１２）　This is a very large source of mechanical stress on the cathode, which causes mechanical deterioration,
　　　　　reduces the electrical contact between the carbon and the sulfur
　　　　 (the path whereby electrons flow to allow the reaction to occur), and prevents the flow of lithium ions
　　　　　to the sulfur surface.

（１３）　Another problem is that lithium and sulfur generally don't react immediately to form Li2S,
　　　　　but rather get there through a series of intermediate species, such as Li2S8, Li2S6, etc.

（１４）　Sulfur itself and Li2S are essentially insoluble in the typical electrolyte used in Li/S cells,
　　　　　but these intermediate "polysulfides" often are soluble, which causes an ongoing
　　　　　and severe loss of sulfur at the cathode.

（１５）　　Other problems appear, such as a roughening of the lithium anode surface with large charge
　　　　　　or discharge currents.

（１６）　　All of these problems result in a basic Li/S cell being a very bad battery.

（１７）　　The Li/S battery chemistry, however, offers the potential for such wonderful battery performance that,
　　　　　　since its discovery in the 1960s, a lot of work has been aimed at solving these problems.

（１８）　　Engineers and scientists have tried putting the sulfur inside nanochannels as well as
　　　　　　using lithium-silicon-carbon alloy anodes, sulfur polymer cathodes, and a host of
　　　　　　other imaginative attempts at solving the interlocked Li/S battery performance limitations.

（１９）　　While a good deal of progress has been made, development of a practical Li/S cell has eluded
　　　　　　researchers for half a century.

（２０）　　The Lawrence Berkeley team addressed these problems by developing a nanocomposite cathode
　　　　　　that addresses the three main problems presented by Li/S cells.

（２１）　　The new cathode material is a sulfur-graphene oxide nanocomposite held together using an elastic polymer binder.

（２２）　　Graphene oxide is formed from graphite oxide by exfoliation, in which an ultrasonic field is applied
　　　　　　to graphite oxide while suspended in water.

（２３）　　The ultrasonic waves peel apart the layers of the graphite oxide, producing very thin flakes of graphene oxide.

（２４）　　These flakes are then given a coating of sulfur a few nanometers in thickness.

（２５）　　The thinness of the sulfur coating allows the sulfur atoms to make good electrical contact
　　　　　　with the graphene oxide flakes.

（２６）　　While not an excellent conductor of electricity, graphene oxide has sufficient conductivity to
　　　　　　anchor the sulfur to the cathode, thereby permitting a large flow of current to pass through the sulfur layers.

（２７）　There are intermediate products (lithium polysulfides) resulting from the operation of a Li/S cell
　　　　　that can dissolve into the ionic electrolyte of the cell, thereby causing sulfur loss
　　　　　and degrading the cell's storage capacity.

（２８）　　One effect of putting the sulfur on the graphene oxide nanoflakes is to protect one side
　　　　　　of the sulfur layer against this degradation.

（２９）　　In the new Li/S cell, a protective surfactant is placed atop the sulfur layer to also
　　　　　　protect its surface against dissolving in the electrolyte.

（３０）　Because the surfactant is cationic (attracted to the sulfur), it will let the lithium anions through
　　　　　to react with the sulfur of the cathode while protecting the sulfur layer.

（３１）　As any lithium polysulfides formed under the surfactant are trapped there, this addition nearly
　　　　eliminates the problem of sulfur loss.

（３２）　To form a useful cathode for an Li/S cell, this loose collection of coated graphene oxide nanoflakes
　　　　　must be bound together to form a nanocomposite with a very large surface area
　　　　　that is accessible to the ionic electrolyte.

（３３）　Similar cells in the past have used 「polyvinylidene fluoride」, a conducting polymer, as a binder material.

（３４）　However, such cells were not able to long survive the enormous change in the volume of the sulfur layers
　　　　　during charge and discharge of the cell.

（３５）　To ameliorate this problem, the Berkeley team substituted an elastomeric co-polymer of
　　　　　styrene butadiene rubber and carboxy methyl cellulose for the binder.

（３６）　The electrolyte was also changed in several ways from the traditional setup
　　　　　(and this being chemistry,　you might need to brace yourself for some challenging terminology here).

（３７）　While the same electrolyte salt 「(lithium bis(trifluoromethanesulfonyl)imide)」 was used,
　　　　the solvent was a mixture of 「n-methyl-(n-butyl) pyrrolidinium bis(trifluoromethanesulfonyl)-imide (PYR14TFSI)」,
　　　　「1,3-dioxolane (DOL), dimethoxyethane (DME)」
　　　　with 1 M 「lithium bis-(trifluoromethylsulfonyl)imide (LiTFSI)」, and 「lithium nitrate (LiNO3)」.

（３８）　This translates to combination which nicely balances the range of operating temperature,
　　　　　viscosity, and ionic conductivity required for efficient Li/S cell operation.

（３９）　The tendency of the cell to form lithium polysulfides was also reduced by the introduction
　　　　　of the DOL and DME fractions.

（４０）　The lithium nitrate was added to reduce damage to the surface of the lithium metal anode,
　　　　　which had been observed to result from multiple charge/discharge cycling.

（４１）　A traditional coated plastic separator (high porosity polypropylene) was used to prevent
　　　　　the flow of electrons through the electrolyte while permitting free flow of the lithium ions.

（４２）　The result of these changes is greatly increased Li/S cell performance.

（４３）　When the Li/S cell was charged and discharged at a 20-hour rate (C=0.05),
　　　　　an initial specific energy of 500 Wh/kg (more than twice that of Li-ion batteries) was still providing
　　　　　as much energy capacity as a fresh Li-ion battery after 1500 charge/discharge cycles.

（４４）　When the charge/discharge rate is increased to a one-hour rate (C=1.0), the energy capacity
　　　　　decreases by a factor of about 40-50 percent, but the cell continues to function well past 1,500 cycles.

（４５）　When the Li/S cells were operated at very large power output
　　　　　 (C=6.0, meaning that a cell would charge or discharge in 10 minutes) even after 150 cycles
　　　　　the specific energy of the cell was larger than that of a fresh and pampered Li-ion cell.

（４６）　This capability for very large power charge and discharge was quite sensitive
　　　　　to the amount of lithium nitrate added to the electrolyte.

（４７）　The potential price point for Li/S cells following the new design is potentially
　　　　　as low as US$100/kWh of storage capacity.

（４８）　Beyond making possible lithium/sulfur batteries with unprecedented specific energy, rate capacity,
　　　　and long cycle life, many of the innovations made by the Berkeley team may also be useful
　　　　in designing better and less expensive Li-ion cells.

（４９）　The Li/S cell for the first time has demonstrated its potential to challenge the dominant Li-ion battery
　　　　　chemistry in the big leagues of electric cars.

[６．３．２Ａ．２]　　　成果

（１）　成果を図１、図２、図３に示す。

    

             図１   A scanning electron micrograph of the nanostructure of the cathode of a Berkeley Li/S cell
                     and a schematic of the layers in the structure ( Lawrence Berkeley Lab)

(This figure is quoted from the document said above)
　　　　　


    

              図２　　Performance curves of a Berkeley Li/S cell. Charge/discharge voltage history at extreme po...
(This figure is quoted from the document said above)
　　　　　

　


   

　　　　　　　　　　　　　　図３

(This figure is quoted from the document said above)
　　　　　


（２）　　電流レート「２Ｃ」では「７００ｍＡｈ/ｇ」の「容量」である。

（３）　　この「ＲＬＳＢ」を搭載した「ＥＶ」の試作車を走らせてほしい。　



[６．３．３Ａ]　　　研究例（３Ａ）　   Graphene Oxide as a Sulfur Immobilizer in High Performance Lithium/Sulfur Cells

  　　　　　　　　　　　　　　　　　　　　Liwen Ji(1),  Mumin Rao(2),  Haimei Zheng(3),  Liang Zhang(4),  Yuanchang Li(5),  Wenhui Duan(5),
  　　　　　　　　　　　　　　　　　　　　Jinghua Guo(4),  Elton J. Cairns(2),  and Yuegang Zhang(1)

(1) The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States

(2)  Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States 
    
     and Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720, United States

(3)  Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States

(4)  The Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States

(5)　Department of Physics, Tsinghua University, Beijing 100084, China

M.R. is a visiting researcher from South China University of　Technology.
L.Z. is a visiting researcher from University of Science and　Technology of China.

　　　　　Received: July 25, 2011
　　　　　18523 dx.doi.org/10.1021/ja206955k |J. Am. Chem. Soc. 2011, 133, 18522–18525
　　　　　Journal of the American Chemical Society COMMUNICATION

[６．３．３Ａ．１]　　　　「ＲＬＳＢ」のシステム

[�T]　　ABSTRACT

（１）　The loss of sulfur cathode material as a result　of polysulfide dissolution causes significant capacity fading
　　　in rechargeable lithium/sulfur cells.

（２）　Here, we use a chemical approach to immobilize sulfur and lithium polysulfides via
　　　the reactive functional groups on graphene oxide.

（３）　This approach enabled us to obtain a uniform and thin (around tens of nanometers) sulfur coating
　　　　on graphene oxide sheets by a simple chemical reactiondeposition strategy and a
　　　　subsequent low-temperature thermal treatment process.

（４）　Strong interaction between graphene oxide and sulfur or　polysulfides enabled us
　　　　to demonstrate lithium/sulfur cells　with a high reversible capacity of 「950-1400 mA h/ g」,
　　　　and stable cycling for more than 50 deep cycles　at 「0.1C」 (1C = 1675 mA/ g).

[�U]　　ＤＥＳＣＲＩＰＴＩＯＮ

（１）　Elemental sulfur (S) is very attractive as a cathode material for high-specific-energy rechargeable
　　　lithium batteries, because a battery based on the lithium/sulfur (Li/S) couple would yield a
　　　theoretical specific capacity of about 「1675 mA h/ g」 with a
　　　theoretical specific energy of 「2600 W h/ kg」 on the assumption
　　　of the complete reaction of Li with S to form Li2S.

（２）　In addition, S is also inexpensive, abundant, and nontoxic.

（３）　Therefore, S is a promising cathode material for high specific energy Li/S　batteries.(1-15 )

（４）　Despite these considerable advantages, there are still a number of challenges in Li/S batteries.

（５）　The first one is the high electrical resistivity of elemental S.

（６）　The second one is the high solubility (in organic solvent electrolytes) of the polysulfide
　　　　ions that are formed during the discharge/charge processes.

（７）　The soluble intermediate Li polysulfides can diffuse through the electrolytetothe
　　　　Li anode wherethey are reducedto form solid precipitates (such as Li2S or Li2S2).

（８）　These reduced products can also diffuse back to the cathode during recharging.

（９）　These issues can lead to low active materials utilization, low coulombic efficiency, and short cycle
　　　　life of the S electrode.(1-15)

（１０）　In order to address these challenges, various carbon and conductive polymer materials have been used to
　　　　　accommodate S, to overcome its insulating property and reduce the
　　　　　dissolution of Li polysulfides, as reported by 「Nazar」, et al.(1,13,15 )and　others.(4,6,7,10,12,16-22)

（１１）　The most recent work by 「Archer」 et al. demonstrated that the mesoporous carbon/S nanocomposites can
　　　　　be cycled for 100 cycles at 「974 mA h/ g 」at a rate of 「0.5C (1C =1675 mA /g)」
　　　　　with the corresponding coulombic efficiency of ∼96% and 94%, respectively,
　　　　　at the first and 100th cycles.(23)

（１２）　　Despite this progress, there are still few reports on fabricating novel CS
　　　　　　cathodes via the chemical reaction approach.(14)

（１３）　　In this work, we used a low-cost and environmentally benign
　　　　　　chemical reaction　deposition strategy to immobilize S on quasi　two-dimensional
　　　　　　graphene oxides (GO) to prepare graphene　oxide　sulfur (GO-S) nanocomposite cathodes
             for Li/S cells in　「ionic liquid-based electrolytes」.

（１４）　　We first deposited nano-S onto graphene oxide (GO) sheets by chemical reaction in a microemulsion
　　　　　　system (see experimental section in the Supporting Information [SI] for details).

　　　　　(Supporting Information is not quoted here.)

（１５）　　Then, we heat treated the assynthesized samples in an argon (Ar) environment at low
　　　　　　temperature (155 C) for 「12 h」 in order to remove some of the
　　　　　　bulk S which is not directly attached to the 「GO」 layers.

（１６）　When the as-synthesized 「GO-S」 nanocomposites were heat-treated in Ar,
　　　　the bulk S on the external surface of the 「GO」 melted and diffused
　　　　into the pores of the 「GO」 due to the strong adsorption effects
　　　　derived from both the high surface area and the functional groups
　　　　on the surface of the 「GO」.

（１７）　At the same time, this low-temperature heat treatment process can partially remove and/or chemically
　　　　　modify some of the functional groups on the 「GO」 surface and  improve the electronic conductivity
　　　　　of the as-prepared 「GO-S」　nanocomposites (see Table 1 in the SI).

（１８）　「Figure 1a」 shows the scanning electron microscope (SEM)
　　　　　image of the as-prepared 「GO-S」 nanocomposite after heat treatment.

（１９）　The layer-like extremely conjugated nanostructures with
　　　　　highly developed porous structures are clearly illustrated.

（２０）　The energy-dispersive X-ray (EDX) microanalysis in (Figure 1b) con-firms the existence of S in the composite.

（２１）　As indicated in the thermogravimetric analysis (TGA), about 66 wt % S is incorporated
　　　　　into the GO after heat treatment (Figure S1, SI: not quoted).

（２２）　The transmission electron microscope (TEM) image in (Figure 2a) and
　　　　　the electron energy-loss spectrum (EELS) in (Figure 2d) indicate that
　　　　　a thin layer of S with a thickness of tens of nanometers is
　　　　　homogenously dispersed on the flake-like 「GO」 surface with no
　　　　　significant fraction of bulk S exposed on the external surface of the
　　　　　sample after heat treatment
　　　　　(For comparison, see the SEM images　for pure 「GO」 and SEM/TEM images for 「GO-S」 nanocomposites in
　　　　　Figures S2 and S3 (SI) before heat treatment ; not quoted).

（２３）　The corresponding elemental mapping of carbon (Figure 2b), and S (Figure 2c) display
　　　　　a very similar intensity distribution, revealing a homogeneous S
　　　　　coating on the 「GO 」flakes in the as-formed 「GO-S」 nanocomposites.

（２４）　The unique structure of the 「GO-S」 nanocomposite can improve
　　　　　　the overall electrochemical performance when it is used as a cathode material for Li/S batteries.

（２５）　　First, it can accommodate the significant volume changes of S as it is converted to Li2S on
　　　　　　discharge, and back to elemental S on recharge.(110,17,24 )

（２６）　In addition, the partially reduced 「GO」 with its large surface area
　　　　　along with ubiquitous cavities can establish more intimate
　　　　　electronic contact with S and avoid aggregation and loss of
　　　　　electrical contact with the current collector.

（２７）　Second, the lowtemperature　heat-treated 「GO」 still contains various kinds of functional groups (Figure S5, SI).

（２８）　These functional groups can have strong adsorbing ability to anchor S atoms and to effectively
　　　　　prevent the subsequently formed Li polysulfides from dissolving
　　　　　in the electrolyte during cycling.

（２９）　　We performed ab initio calculations to clarify the role of
　　　　　functional groups on 「GO」 in immobilizing S (see the calculation
　　　　　　methods and detailed results in the SI).

（３０）　The results indicated that
　　　　　both epoxy and hydroxyl groups can enhance the binding of S to
　　　　　the CC bonds due to the induced ripples by the functional
　　　　　groups (Figure 3a).

（３１）　　We also performed soft X-ray absorption
　　　　　spectroscopy (XAS) measurement which probes unoccupied electronic
　　　　　structure and thus is a powerful tool for probing chemical bonding in surface chemistry.

（３２）　　(Figure 3b) shows the carbon K-edge absorption
　　　　　spectra for both 「GO」 and 「GO-S」 nanocomposites
           (see S K-edge　spectrum in Figure S7, SI ; not quoted).

（３３）　　The absorption features “A”, “D”, and 

　　　　　　 “E”, which can be attributed to the π* state, excitonic state, and σ*
　　　　　　state,25 are observed for both samples.
              Of note in the spectra is　the increase in the sharpness of the π* and excitonic state for GOS
　　　　　　nanocomposites as compared with GO, suggesting that the ordering of the sp2
　　　　　　-hybridized carbon structure is better formatted　after S is incorporated.

（３４）　In addition, feature “C” originating from a different functional group (possibly the CO bond)
　　　　on the GO are weakened significantly when incorporated with S,
　　　　which means strong chemical interaction between S and the
　　　　　functional group of 「GO」 happens and S can partially reduce the 「GO」.(26)

（３５）　Besides, a new feature “B”, originating from the CS σ*
　　　　　excitations,27 is observed for the 「GO-S」 nanocomposites.

（３６）　We evaluated the electrochemical Li storage capability of these heat-treated 「GO-S」 nanocomposites
　　　　　as potential cathode materials for Li/S cells in the n-methyl-(n-butyl) pyrrolidinium bis-
　　　　　(trifluoromethanesulfonyl)imide (PYR14TFSI), Li-bis(trifluoromethylsulfonyl)imide
　　　　　(LiTFSI), and poly(ethylene glycol)
　　　　　dimethyl ether (PEGDME, Mw = 250) mixture-based electrolyte.

（３７）　(Figure 4a) shows the cyclic voltammetry (CV) profile of one electrode.

（３８）　The measurement was conducted at a scan rate of 0.05 mV s1 in the voltage range of 1.0 to 3.6 V vs Li/Li+.

（３９）　During the first cathodic scan, three main reduction peaks at around 2.4, 2.1, and 1.8 V were clearly shown.

（４０）　According to the reported mechanisms for oxidation and reduction of S during discharge/
　　　　　charge,(5,6,10,18,19,2831) the peak at around 2.4 V can be assigned
　　　　　to the reduction of elemental S to higher-order Li polysulfides (Li2Sn, n ≧8).

（４１）　The peak at about 2.1 V probably corresponds to
　　　　　the reduction of higher-order Li polysulfides to lower-order Li
　　　　　polysulfides (such as Li2S6, Li2S4) from Li2S8.　(5,6,10,16-21,28-31)

（４２）　The peak at 1.8 V is related to the reduction of polysulfide species to form Li2S.

（４３）　In the subsequent anodic scan, only one sharp oxidation peak is observed at about 2.6 V that is attributed to the
　　　　　complete conversion of Li2S and polysulfides into elemental S.

（４４）　The main reduction peak is shifted to slightly higher potential
　　　　　and the oxidation peaks to lower potentials with increase in cycle
　　　　　number, indicating an improvement of reversibility of the cell with cycling.

（４５）　In addition, as the cycle number increased, the oxidation peak at 2.6 V becomes less significant,
　　　　　while another new one at 2.35 V grows higher in intensity.

（４６）　The oxidation peak at 2.35 V is associated with the formation of Li2Sn (n > 2).(23,29)

（４７）　After the second cycle, both the CV peak positions and peak
　　　　　currents undergo very small changes, indicating relatively good capacity retention.

（４８）　The CV results show that 「GO」 can help to
　　　　　prevent S from dissolving into the electrolyte because of its large
　　　　　surface along with some functional groups on the surface.

（４９）　Figure 4b depicts the first and second cycle discharge/charge
　　　　　typical voltage profiles of the electrodes at the 「0.02C rate (1C = 1675 mA/ g) 」between 1.0 and 3.0 V.
　　　　　(The capacity values in this article are calculated according to the mass of S.)

（５０）　All the discharge curves show three plateaus in the voltage profile that
　　　　　are consistent with the peaks in the CV and are also well
　　　　　documented in the literature.(5,6,10,16,18-21,23,28)

（５１）　The GO-S nanocomposite delivers a high initial discharge capacity of about
　　　　「1320 mA h/ g」 at「 0.02C」.

（５２）　The corresponding coulombic effi-ciency in the first discharge/charge cycle is 96.4%.

（５３）　At the second cycle, a large reversible capacity of about 「1247 mA h/ g」 is
　　　　　preserved (97.5% coulombic efficiency), corresponding to about 94.5% capacity retention.

（５４）　This initial capacity loss is small compared
　　　　　to the formerly reported results of similar materials,(16,32) indicating
　　　　　that the strong 「GO-S」 interaction can reduce the dissolution of the
　　　　　lithium polysulfides into the electrolyte and thus minimize the shuttle phenomenon.

（５５）　 (Figure 4c) shows the cycling performance of the same cell cycled at a rate of 「0.1C」
　　　　　after the initial two cycles at 「0.02C」.

（５６）　The discharge capacity of the first cycle at 「0.1C」 remains at around 「1000 mA h/ g」.

（５７）　At the second cycle at 0.1C, this value decreases to about「 950 mA h/ g」.

（５８）　However, after more than 「50 cycles」 at the same rate, the reversible capacity remains at 「954mA h /g」
　　　　　(with a coulombic efficiency of about 96.7%), indicating
　　　　　very stable reversibility of the electrochemical reactions and excellent
　　　　　capacity retention (also see the cycle performance of another coin cell in Figure S10, SI).

（５９）　The GO-S nanocomposites display improved coulombic efficiencies compared to the former reports.23

（６０）　The discharge capacity of the GO-S was highly reproducible over many coin cells.

（６１）　　Another example of the electrochemical
　　　　　　performance of the 「GO-S」 electrode is demonstrated in (Figure 4d)
　　　　　　where a cell showed a reversible capacity of 「735 mA h /g」 at「 0.5C」 after「 30 cycles 」at various rates.

（６２）　Further cycling at a low rate of 「0.05 C」 brings it back to a reversible capacity of about「 1100 mA h/ g」 for
　　　　　another 「20 cycles」.

（６３）　When this coin cell was discharged at a higher rate of 「1C」, a reversible capacity of about 「550 mA/ g」 was obtained.

（６４）　The last decrease of the rate to 「0.2C」, yielded a reversible capacity of about 「890 mA h/ g」.

（６５）　When this coin cell was further discharged at 「2C」, an acceptable reversible capacity of
　　　　about 「370 mA h/ g」 was obtained, indicating excellent capacity reversibility and high rate performance
　　　　(see the corresponding discharge/charge profiles in Figure S11, SI.;  not quoted)

（６６）　The 「GO」 clearly performs very well as a means to stabilize the S electrode.

（６７）　　The 「GO」 provides highly reactive functional groups on
　　　　　　its surface that can serve as immobilizers to hold the S.(1,5,8)

（６８）　Also, by limiting the concentration of the polysulfide anions in the
　　　　electrolyte, the redox shuttle phenomenon is largely avoided.(1,8,9)

（６９）　The intimate contact of the S provided by the large surface area
　　　　　and the functional groups on 「GO」 is favorable to good electron/
　　　　　ion accessibility, leading to enhanced cycle performance and rate capability.(19,17,20)

（７０）　In addition, the optimized 「ionic liquid-based　electrolytes」 which have suitable viscosities and wetting properties
　　　　　influence the penetration of electrolyte into the S electrode structure,
　　　　　while increasing the ionic conductivity within the
　　　　　electrodes at the same time
　　　　　 (see control experiment in LiTFSIPEGDME-based　electrolyte in Figure S12, SI　; not quoted).(5,33,34)

（７１）　In summary, a novel chemical approach is employed to　synthesize a 「GO-S」 nanocomposite
　　　　　to immobilize S in the　cathode material of Li/S cells.

（７２）　The 「GO-S」 nanocomposite cathodes display good reversibility, excellent capacity stability
　　　　　of about 「1000 mA h/ g」, and rate capability of up to 「2C」 in ionic liquid-based electrolyte.

（７３）　The 「GO」 in the heat-treated composites has good conductivity and an extremely high surface area, and
　　　　　provides a robust electron transport network.

（７４）　The functional groups on the 「GO」 surface play the role of immobilizers that keep
　　　　　intimate contact of the conducting matrix with S species, and
　　　　　effectively confine any polysulfides from dissolving.

（７５）　The 「GO」 network also accommodates the volume change of the electrode
　　　　　during the LiS electrochemical reaction.

（７６）　As a result, reversibility and high rate discharge capability were obtained.

（７７）　The same strategy could be helpful to explore and develop new porous
　　　　　carbon(35,36) or conductive polymer-based S nanocomposite cathodes for advanced Li/S cells.

[�W]　　　REFERENCES

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(2) Hassoun, J.; Scrosati, B. Angew. Chem., Int. Ed. 2010, 122, 2421–2424.

(3) Kolosnitsyn, V.; Karaseva, E. Russ. J. Electrochem. 2008, 44, 506–509.

(4) Yang, Y.; McDowell, M. T.; Jackson, A.; Cha, J. J.; Hong, S. S.;
     Cui, Y. Nano Lett. 2010, 10, 1486–1491.

(5) Shim, J.; Striebel, K. A.; Cairns, E. J. J. Electrochem. Soc. 2002, 149, A1321–A1325.

(6) Choi, Y.-J.; Chung, Y.-D.; Baek, C.-Y.; Kim, K.-W.; Ahn, H.-J.;
    Ahn, J.-H. J. Power Sources 2008, 184, 548–552.

(7) Liang, C.; Dudney, N. J.; Howe, J. Y. Chem. Mater. 2009,  21, 4724–4730.

(8) Ji, X.; Nazar, L. F. J. Mater. Chem. 2010, 20, 9821–9826.

(9) Gao, X.-P.; Yang, H.-X. Energy Environ. Sci. 2010, 3, 174–189.

(10) Lai, C.; Gao, X. P.; Zhang, B.; Yan, T. Y.; Zhou, Z. J. Phys. Chem. C 2009, 113, 4712–4716.

(11) Ryu, H.-S.; Ahn, H.-J.; Kim, K.-W.; Ahn, J.-H.; Lee, J.-Y. J. Power Sources 2006, 153, 360–364.

(12) Wang, J.; Yang, J.; Xie, J.; Xu, N. Adv. Mater. 2002, 14, 963–965.

(13) Ji, X.; Evers, S.; Black, R.; Nazar, L. F. Nat. Commun. 2011, 2, 325.

(14) Wang, H.; Yang, Y.; Liang, Y.; Robinson, J. T.; Li, Y.; Jackson,
     A.; Cui, Y.; Dai, H. Nano Lett. 2011, 11, 2644–2647.

(15) He, G.; Ji, X.; Nazar, L. Energy Environ. Sci. 2011, 4, 2878–2883.

(16) Cao, Y.; Li, X.; Aksay, I. A.; Lemmon, J.; Nie, Z.; Yang, Z.; Liu, J.
Phys. Chem. Chem. Phys. 2011, 13, 7660–7665.

(17) Chen, S.-R.; Zhai, Y.-P.; Xu, G.-L.; Jiang, Y.-X.; Zhao, D.-Y.; Li,
　　　J.-T.; Huang, L.; Sun, S.-G. Electrochim. Acta 2011, 56, 9549–9555.

(18) Jeon, B. H.; Yeon, J. H.; Kim, K. M.; Chung, I. J. J. Power Sources　2002, 109, 89–97.

(19) Liang, X.; Wen, Z.; Liu, Y.; Zhang, H.; Huang, L.; Jin, J. J. Power　Sources 2011, 196, 3655–3658.

(20) Wang, J.; Chew, S. Y.; Zhao, Z. W.; Ashraf, S.; Wexler, D.; Chen,
　　J.; Ng, S. H.; Chou, S. L.; Liu, H. K. Carbon 2008, 46, 229–235.

(21) Yuan, L. X.; Feng, J. K.; Ai, X. P.; Cao, Y. L.; Chen, S. L.; Yang,
　　　　H. X. Electrochem. Commun. 2006, 8, 610–614.

(22) Wang, J.; Chen, J.; Konstantinov, K.; Zhao, L.; Ng, S. H.; Wang,
      G. X.; Guo, Z. P.; Liu, H. K. Electrochim. Acta 2006, 51, 4634–4638.

(23) Jayaprakash, N.; Shen, J.; Moganty, S. S.; Corona, A.; Archer,
     L. A. Angew. Chem., Int. Ed. 2011, 50, 5904–5908.

(24) Ji, L.; Tan, Z.; Kuykendall, T. R.; Aloni, S.; Xun, S.; Lin, E.;
     　Battaglia, V.; Zhang, Y. Phys. Chem. Chem. Phys. 2011, 13, 7170–7177.

(25) Skytt, P.; Glans, P.; Mancini, D. C.; Guo, J. H.; Wassdahl, N.;
     Nordgren, J.; Ma, Y. Phys. Rev. B 1994, 50, 10457.

(26) Chen, W.; Yan, L.; Bangal, P. R. J. Phys. Chem. C 2010, 114, 19885–19890.

(27) Pasquali, L.; Terzi, F.; Montecchi, M.; Doyle, B. P.; Lukkari, J.;
      Zanfrognini, B.; Seeber, R.; Nannarone, S. J. Electron Spectrosc. Relat.
      Phenom. 2009, 172, 114–119.

(28) Yamin, H.; Peled, E. J. Power Sources 1983, 9, 281–287.

(29) Aurbach, D.; Pollak, E.; Elazari, R.; Salitra, G.; Kelley, C. S.;
     Affinito, J. J. Electrochem. Soc. 2009, 156, A694–A702.

(30) Jung, Y.; Kim, S. Electrochem. Commun. 2007, 9, 249–254.

(31) He, X.; Pu, W.; Ren, J.; Wang, L.; Wang, J.; Jiang, C.; Wan, C.
　　　Electrochim. Acta 2007, 52, 7372–7376.

(32) Wang, J.-Z.; Lu, L.; Choucair, M.; Stride, J. A.; Xu, X.; Liu, H.-K.
J. Power Sources 2011, 196, 7030–7034.

(33) Shin, J. H.; Cairns, E. J. J. Power Sources 2008, 177, 537–545.

(34) Shin, J. H.; Cairns, E. J. J. Electrochem. Soc. 2008, 155, A368–A373.

(35) Long, J. W.; Dunn, B.; Rolison, D. R.; White, H. S. Chem. Rev. 2004, 104, 4463–4492.

(36) Ji, L.; Lin, Z.; Alcoutlabi, M.; Zhang, X. Energy Environ. Sci. 2011, 4, 268

[６．３．３Ａ．２]　　　　結果

（１）　結果を図１、図２、図３、図４に示す。

   
 
             図１　　 SEM image (a) and EDX spectrum (b) of the GO-S nanocomposite
　　　　　　　　　　　after heat treatment in Ar at 155

(This figure is quoted from the document said above)
　　　　　



    

　　　　　　　　　図２　　 TEM bright field (BF) image (a) and the corresponding
　　　　　　　　　　　　　　elemental mapping for carbon (b) and S (c) reveal a homogeneous S
　　　　　　　　　　　　　　coating on the GO flakes. EELS spectrum is shown in (d).
　　　　　　　　　　　　　　The scale bars　are 50 nm.
(This figure is quoted from the document said above)
　　　　　




    

　　　　　　　　　　図３　　 (a) Representative pattern of GO immobilizing S.
　　　　　　　　　　　　　　　　　The　hydroxyl enhances the binding of S to the CC bond due to the
　　　　　　　　　　　　　　　　　induced ripples by epoxy or hydroxyl group.
　　　　　　　　　　　　　　　　　Yellow, red, and white balls　denote S, O, and H atoms, respectively,
　　　　　　　　　　　　　　　　　while the others are C atoms.
　　　　　　　　　　　　　　　　　Note that the C atoms bonding to S or O are highlighted as blue balls.
　　　　　　　　　　　　　　　(b) C K-edge XAS spectra of GO and GO-S nanocomposites after heat
　　　　　　　　　　　　　　　　　treatment in Ar at 155 C for 12 h.

　　　(This figure is quoted from the document said above)
　　　　　


    

　　　　　　　図４ 　 (a) CV curve at 0.05 mV s1 scanning rate;
　　　　　　　　　　　 (b) galvanostatic　discharge/charge profiles at 0.02C rate;
　　　　　　　　　　　 (c) cycling performance at a　constant current rate of 0.1C after initial activation processes at 0.02C
　　　　　　　　　　　　　　for two cycles;
　　　　　　　 　　　　(d) reversible capacity vs current density (rate capability).
　　　　　　　　　　　　　The GO-S nanocomposites were heat treated in Ar environment at　155 C for 12 h.

(This figure is quoted from the document said above)
　　　　　

[６．３．３Ａ．３]　　　評価

（１）　「グラフェン・オキサイド」の効果が主張されている。

（２）　「電流レート」が「２Ｃ」だと「４００ｍＡｈ/ｇ」まで容量が落ちるからまだ実用的ではない。



[６．３．４Ａ]　　　　研究例（４Ａ） 

                          Energy & Environmental Science Issue 10, 2014

                         Improved lithium–sulfur batteries with a conductive coating on the separator to prevent
                         the accumulation of inactive S-related species at the cathode–separator interface

                         Hongbin Yao,(a) ,  Kai Yan,(a),   Weiyang Li,(a),   Guangyuan Zheng,(b),   Desheng Kong,(a),  
                         Zhi Wei Seh,(a),   Vijay Kris Narasimhan,(a),   Zheng Lianga and  Yi Cui,(a,c)  

                            Energy & Environmental Science,  2014,7,  3381-3390
                            DOI: 10.1039/C4EE01377H
                            Received 03 May 2014, Accepted 14 Jul 2014
                            First published online 07 Aug 2014 
 

[６．３．４Ａ.1]　　　　「ＲＬＳＢ」のシステム　　　　

 （１）　Improved lithium–sulfur batteries with a conductive coating
　　　　on the separator to prevent the accumulation of inactive S-related species
　　　　at the cathode–separator interface　bottom

（２）　　 Lithium–sulfur (Li–S) batteries are highly attractive for future generations of portable electronics
    　　　and electric vehicles due to their high energy density and potentially low cost.

（３）　　 In the past decades, various novel electrodes and electrolytes have been tested
    　　　　to improve Li–S battery performance.

（４）　 However, these designs on electrodes and electrolytes have not fully addressed the problem
    　　　of low cycling stability of Li–S batteries.

（５）　 Here, we show the role of the separator in the capacity decay of the Li–S battery,
    　　namely that it can accommodate a large amount of polysulfides inside which then precipitates
    　　　as a thick layer of inactive S-related species.

（６）　 Using a thin conductive coating on the separator to prevent the formation of the inactive
     　　S-related species layer, we show that the specific capacity and cycling stability
　　　　of the Li–S battery are both improved significantly compared to the battery　with a pristine separator.

（７）　　  Combining this separator design with a monodisperse sulfur nanoparticle cathode,
     　　　we show Li–S batteries with a life of over　「500 cycles」 with an initial specific capacity
   　  　　of 「1350 mA h/ g」  at「 C/2」 and a cycle decay as low as 「0.09% 」per cycle.

[６．３．４Ａ．２]　　　　　　結果

（１）　　結果を図１に示す。



    

                 図１　


(This figure is quoted from the document said above)
　　　　　

（２）　「電流レート」は「０．５Ｃ」である。

（３）　「５００サイクル」の後でも「１３５０ｍＡｈ/ｇ」の容量を維持しており、　「０．０９％」しか劣化していない。

（４）　かなり実用的レベルに達しているのではないか？



＊＊＊＊＊＊＊  Ａ　ＰＡＲＴ　END ＊＊＊＊＊＊＊＊


[６．３．１]　　　研究成果（１）　　

　　　　　Improving lithium-sulfur batteries for greater energy density

　　　　　(September 26, 2014) Paul Dvorak


[６．３．１．１]　　　　「ＲＬＳＢ」のシステム

（１）  This article comes from Nano Letters and will be of interest to who wish to stabilize their grids.
        A search for the next great high-energy, rechargeable battery technology has been on for a while.

（２）　Recently, scientists report they have overcome key obstacles toward making lithium-sulfur (Li-S) batteries,
　　　 which have potential to outperform today’s lithium-ion technology.

（３）　This study appears in the ACS journal Nano Letters.

（４）　To better confine the sulfur/polysulfides in the electrode of lithium–sulfur (Li/S) batteries
　　　　and improve the cycling stability, we developed a double-layered core–shell structure
　　　　of polymer-coated carbon–sulfur.

（５）　　Carbon–sulfur was first prepared through the impregnation of sulfur into hollow carbon spheres
　　　　　under heat treatment, followed by a coating polymerization
　　　　to give a double-layered core–shell structure.

（６）　　From the study of scanning transmission electron microscopy images,
　　　　we demonstrated that the sulfur successfully penetrated through the porous carbon shell
　　　　and aggregated along the inner wall of the carbon shell, which, for the first time,
　　　　provided visible and convincing evidence that sulfur preferred diffusing into the hollow carbon rather
　　　　than aggregating in/on the porous wall of the carbon. 

（７）　　Xingcheng Xiao, Weidong Zhou, Mei Cai and colleagues point out that the capabilities of lithium-ion batteries,
　　　　　which power many of our consumer electronics, as well as electric vehicles, have largely plateaued.

（８）　　Scientists have been pursuing a number of new battery technologies to topple today’s standard.

（９）　　One heavy focus has been on a key battery component that is currently made out of a metal oxide.

（１０）　　Some researchers have been trying to replace the metal oxide with cheaper and lighter sulfur,
　　　　　to make Li-S batteries.

（１１）　　In theory, this could allow batteries to pack five to eight times the energy of existing technology.

（１２）　　One of the main problems with this approach, however, is that Li-S compounds escape from where
　　　　　　they’re supposed to be, which causes the battery to lose charge quickly.

（１３）　　The team set out to find a way to contain the errant compounds.

（１４）　　To solve the problem, the researchers made tiny, hollow shells out of carbon, which is conductive.

（１５）　　They then coated them with a polymer to help confine the Li-S compounds inside.

（１６）　　When tested, the structures kept up a high-energy storage capacity
　　　　　 (630 mAh/g versus less than 200 mAh/g of lithium-ion batteries) over 600 cycles
　　　　　of fast charging and discharging.

（１７）　　“These results provide promising insights and novel concepts for future sulfur-based batteries,”
　　　　　　the researchers conclude.

[６．３．５．２]　　　　　研究結果

（１）　　図１に研究結果を示す。



    

            図１　　


（ＴＨＩＳ　ＦＩＧＵＲＥ　ＩＳ　ＫＵＯＴＥＤ　ＦＲＯＭ　ＴＨＥ　ＤＯＣＵＭＥＮＴ　ＳＡＩＤ　ＡＢＯＶＥ）


（２）　電流レートは　「Ｃ/３」のデータである。 

（３）　「５００サイクル」では「７００ｍＡｈ/ｇ」の容量が得られている。



[６．３．６]      研究成果（６）

　　　　「イオン液体」を用いた次世代リチウム二次電池の構築

　　　　渡邉正義　　　　横浜国立大学大学院工学研究院


[６．３．６．１]      リチウム硫黄電池のシステム　　

（１）　 はじめに「リチウム二次電池」の高エネルギー密度化、高出力密度化、大型化により、
　　　　その安全性への要求も高まっている。

（２）　 現在市販されている「リチウム・イオン電池」の「電解質」には、可燃性、揮発性の「有機溶媒」が使われており、
　　　　電池の安全性確保のため「電解質」の難燃化や過充電防止など様々な観点から研究開発がなされている。

（３） 　近年、「室温溶融塩」である「イオン液体」を「電解質」に用いた電池に関する研究が世界的に展開されている。

（４）　「イオン液体」とは、「イオン」のみで構成される液体で、その構成イオンは「分子性溶媒」がないにもかかわらず
　　 　電離しており、「イオン液体」を構成する「カチオン」、「アニオン」の組み合わせによっては
　　 　室温以下の温度で液体状態を示す。

（５）　これが、「水」、「有機溶媒」に続く第三の液体として電気化学分野のみならず、
　　　　物理化学、合成化学、材料科学など様々な分野で注目を集めている (1-4)。

（６）　「イオン液体」は一般に、（１） 難燃性・難揮発性、（２） 広い液体温度域、（３） イオン伝導性、
　　　　（４） 高いイオン濃度、（５） 電気化学的安定性、といった特徴を有する。

（７）　「リチウム電池用電解質」への適用を目指す検討も、電池の安全性向上にためにこのような特徴を
　　　　生かせるとの期待に基づいている。

（８）　本講演では、「イオン液体」を「リチウム硫黄二次電池」に適用した例を紹介する。



[６．３．６．２]　　溶媒和イオン液体とリチウム硫黄電池の構築

（１）　ある種のグライム（triglyme(G3) or tetraglyme(G4)）−リチウム塩(1:1)錯体がIL 類似の特性を示し、
　　　　「溶媒和IL」 と見なせる事を見出した(5-10)。

（２）　この「溶媒和IL」 の持つ特徴を生かした展開を摸索した。

（３）　「硫黄」は「１６７２ｍＡｈ/ｇ」 の蓄電容量を持ち、かつ安価で資源的制約の無い物質であるため、
　　　 「正極材料」として古くから期待されている。

（４）　しかし、（１） 硫黄およびその還元生成物の絶縁性、（２） 遅い電極反応速度、
　　　　（３） 「活物質」（特に硫黄の「還元生成物」である「 Li2Sn: n = 8-1」）の「電解質」への溶出の問題などから
　　　　未だ実用化には至っていない。

（５）　特に（３）の溶出の問題を解決するために、これまで無機あるいは高分子の「固体電解質」を用いた検討が
　　　進められてきた。

（７）　 「IL」 の溶質に対する配位性は弱い。

（８）　　硫黄の「還元生成物」である「 Li2Sn」が「電解質」に溶出するためにはこれが溶媒和される必要があるが、
　　　　　「IL」 には溶出し難いと考えられた (8)。

（８）　　そこで、多孔構造を有する炭素を硫黄の担体に用いて正極を作成し (11)、
　　　　グライム−Li[(CF3SO2)2N] 錯体を電解質とした、「リチウム―硫黄電池」の特性を検討した12, 13)。

（９）　　その結果、「Li2Sn」 の溶出を著しく抑制できることを見出した(13)。

（１０）　汎用の「電解液」である、「1 M LiPF6-EC/DEC 」などを用いると、一回目の放電では「２００ｍＡｈ/ｇ」 程度の容量は
　　　　　得られるが２ 回目以降の充放電は全く不可能で、電極活物質は完全に溶出し、
　　　　　さらに「Sn 2-」 と溶媒との間の副反応も起こる (12)。

（１１）　さらに「活物質」の溶出が顕著な系では、「充電容量」が「放電容量」より著しく高くなる
　　　　　いわゆる「レドッス・サイクリング」が生起し、理論放電容量以上の充電が起こることも見られるが、
　　　　　グライム錯体を電解質に用いるとまったくこのような傾向は現れない。

（１２）　すなわち（３）の問題は「グライム錯体」を用いることによって回避できた。

（１３）　　この「リチウム硫黄電池」の「クーロン効率」は「４００サイクル」の間「９８％」以上、
　　　　 　「４００ 回」の充放電後も 「７００ｍＡｈ/ｇ（S）」 程度の容量を維持した。(Fig. 1 NOT EXPRESSED )(13)。

（１４）　　さらに、適当なブロック共重合体を用いると、溶媒和構造を壊さずに薄膜化も可能となった。

（１５）　　今後の成果に期待が持てると考えている。


 [参考文献]

(1) 最先端材料システムOne Point 2：イオン液体, 高分子学会編, 共立, 2012.

(2) イオン液体の科学，イオン液体研究会監修，丸善，2012.

(3) Macromolecules (Review), 41, 3739 (2008).

(4) Bull Chem. Soc. Jpn. (Accounts), 85, 33 (2012).

(5) Chem. Lett., 39, 753 (2010).

(6) J. Phys. Chem. C, 115, 18384 (2011).

(7) J. Phys. Chem. B, 116, 11323 (2012).

(8) J. Am. Chem. Soc., 133, 13121 (2011).

(9) J. Power Sources, 195, 6095 (2010).

(10) J. Electrochem. Soc., 158, A769 (2011).

(11) J. Electrochem. Soc., 155, K42 (2008).

(12) Chem. Commun., 47, 8157 (2011).

(13) J. Electrochem. Soc., 160, A1304 (2013)



[６．３．７]　　　　研究成果（７）

　　　　「オークリッジ・ナショナル研究所」の研究成果

　　　　All-solid lithium-sulfur battery stores four times the energy of lithium-ions  

　　　　Dario Borghino   June 7,  2013

[６．３．７．１]　　　　リチウム硫黄電池のシステム

（１）　Researchers at the 「Oak Ridge National Laboratory (ORNL)」 have come up with a promising design
　　　　for a lithium-sulfur rechargeable battery that is considerably cheaper
　　　　and more energy-dense than standard lithium-ions.

（２）　Using a solid electrolyte rather than a liquid one, the battery is also testing much safer
　　　　and more durable than previous designs.

（３）　「Lithium-sulfur batteries」 are seen by some as the successors of 「lithium-ions」 because they are extremely
　　　　light (they are often used for solar-powered flight ), they can reach an impressive energy density,
　　　　and they are cheaper to produce.

（４）　But the technology isn't quite mature yet, and as it turns out, the two major limitations
　　　　with Li-S batteries have to do with the electrolyte.

（５）　　An electrolyte is a substance that, when mixed with a solvent, releases ions, making it electrically conductive.

（６）　　In batteries, electrolytes transport charge between the two electrodes, converting chemical energy
　　　　into electrical energy.

（７）　　In previous Li-S battery designs, the electrolyte used was liquid in nature.

（８）　　This proved a double-edged sword:
　　　　　the liquid electrolyte is an excellent conductor because of how it dissolves the lithium compounds,
　　　　　but this dissolution also causes the battery to break down prematurely.break down prematurely.

（９）　　The liquid electrolyte is also flammable, posing serious safety concerns.

（１０）　　But now, researchers may have found a way around these problems.

（１１）　　"Our technology overcomes the capacity fade and safety issues of Li-S technology,"
　　　　　　Dr. Chengdu Liang, lead author of a paper on the research, told Gizmag.

（１２）　　"The battery still performs well after a few hundred cycles, and the volumetric density could be
　　　　　　slightly better than Li-ion batteries."

（１３）　The researchers overcame these barriers by building a 「solid electrolyte」 made of
　　　　「lithium polysulfidophosphates」 (a new class of sulfur-rich materials with good electrical conductivity)
　　　　to create an energy-dense, all-solid battery that is showing a lot of promise.

（１４）　Even after　「 300 charge-discharge cycles」 at 「60°C (140ºF)」, the battery retained
　　　　a capacity of 「1200 mAh/g」, compared to the 「140-170 mAh/g」　of a traditional 「lithium-ion battery」
　　　　(lithium-sulfur batteries,　however, only deliver about half the voltage of lithium-ions, so this 8-fold increase
　　　　　actually translates　into a 4-fold increase in energy density).

（１５）　The battery uses elemental sulfur, which is a byproduct of industrial petroleum processing.

（１６）　　In other words, the battery could also provide a way to recycle industrial waste into a useful – perhaps
　　　　　even superior – technology.

（１７）　　"The main limitation is the relatively low ionic conductivity of the solid electrolyte,"
　　　　　　said Liang.

（１８）　　"So the power density is lower than Li-ion batteries, but it can be improved with a better solid electrolyte.
　　　　　　Moreover, the ceramic structure is brittle, and much optimization is needed."

（１９）　　The technology is still in the early stages of development, but Liang and colleagues are working on ironing out
　　　　　these issue and have filed a patent application for their battery design.

（２０）　　The paper detailing the study was recently published in the journal　「Angewandte Chemie」.

（２１）　　Gizmag wrote back to Dr. Chengdu Liang for more details of the battery's charging and discharging behavior.

（２２）　　Here is his response:

（２３）　　"We did not observe self-discharge.
　　　　　　A charged cell was put on shelf for over a week, and it still delivered the same capacity.

（２４）　　The essence of our all-solid battery design is to eliminate the self-discharge
　　　　　　through the all-solid configuration.

（２５）　　"This battery charges slower than Li-ion battery at the current status for a simple reason;
　　　　　　the ionic conductivity of both the solid electrolyte and cathode are not high energy
　　　　　　to have high current density.
　　　　　　Much better performance at elevated temperatures such as 60 degrees C or higher."

[６．３．７．２]　　　　成果

（１）　　「３００回」の充放電サイクルの後でも「６０℃」において
　　　　 「１２００ｍＡｈ/ｇ」の容量を維持している。

（２）　　現行の「リチウム・イオン電池」の「１４０−１７０ｍＡｈ/ｇ」の「電流容量」に比較して
　　　　 「電流容量」では「８倍」であるが、「電圧」が「半分」であることを考慮すると、
　　　　「重量エネルギ密度」としては「４倍」になる。

（３）　しかし「固体電解質」では「出力密度」は「リチウム・イオン電池」に比べて小さいのが課題である。



[６．３．８]　　　　研究成果（８）　　　Impressive graphene-based cathode for lithium-sulfur batteries

　　　　　　　　　　　　　　　　　　　　　Graphene applications Batteries Technical / Research

　　　　　　　　　　　　　　　　　　　　　Source: cleantechnica　　Apr 20, 2015 

[６．３．８．１]　　　　リチウム硫黄電池のシステム

（１）　Researchers at Beihang University in China developed new cathode materials
　　　　for lithium-sulfur batteries, made from vertically aligned sulfur–graphene (S-G) nanowalls
　　　　on electrically conductive substrates.

Impressive cathode for lithium-sulfur batteries image

（２）　These new cathodes are reported to allow fast diffusion of lithium ions and electrons
　　　　and achieve an excellent capacity
　　　　(of 1261 mAh g–1 in the first cycle, and over 1210 mAh g–1 after 120 cycles)
　　　　and high-rate performance (more than 400 mAh g–1 at 8C, 13.36 A g–1).

（３）　The scientists claim that these impressive figures position it as the best demonstrated rate performance
　　　　for sulfur-graphene cathodes.

（４）　The researchers believe that this new work may open the door to new approaches
　　　　to the manufacture of graphene-containing composites with unique structures
　　　　“for catalysis, sensors, and energy storage and conversions.”

[６．３．８．２]   研究結果

（１）　図１に結果を示す。


   

　　　　　　　　　　　　　　　　　　図１　　　


（THIS FIGURE IS QUOTED FROM THE DOCUMENT SAID ABOVE)


（２）　電流レートは「２Ｃ」で容量は「７００ｍＡｈ/ｇ」もある。

（３）　充分に実用的レベルに達している。

（４）　この「ＲＬＳＢ」を搭載した「ＥＶ」の「試作車」を走らせてほしい。

 

　

　　　　
　　　　　　　
　　　　　　 　　 　   　　　   　　　　 

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                 JOHANNES VERMEER