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Beyond Lithium Ion Batteries

Beyond Lithium Ion Batteries

R oughly40%of total U.S.energy consumption is devoted to electricity generation and another30%to trans-portation.It is now well recognized that electrochemical energy storage,that is,batteries,could do much to wean us from a fossil fuel economy in these arenas.For example,batteries could do much to simplify the integration of intermittent wind and solar renewables into the electrical grid.However,there are at present more economic means to account for the variability (demand management,increasing grid interconnects,?exible generation from conventional sources,etc.)and even far cheaper energy storage options(pumped hydro,compressed air).Thus,integration of extensive electrochemical energy storage with the grid should be viewed only in terms of a long-term goal unless a new very cheap battery chemistry is developed.1In contrast,conversion of road transport from low-e?ciency internal combustion engines to higher-e?ciency electric vehicles(EVs)is now beginning in earnest,with partial electri?cation via hybrids(HEV)already representing>3%of all new car sales in the U.S.The principle issue today confronting complete electri?cation of road transport is simply a battery problem,that is,developing a cost-e?ective,safe,and long-lived battery with su?cient energy storage(both in terms of weight and volume)to give enough range for daily driving so that charging can be accomplished overnight at home.

The king of batteries today for EVs and HEVs(as well as consumer electronics)is the rechargeable Li ion battery.In this battery,Li+ions are shuttled by a Li salt dissolved in a nonaqueous liquid solvent between intercalation in a graphite anode and intercalation in a transition-metal oxide cathode,for example,LiCoO2.Over the past~25years,commercial Li ion batteries have improved continuously in terms of cost,lifetime, energy densities,and other metrics.However,the increase in terms of energy densities,especially gravimetric,is quite limited.This has led many to believe that mass market adoption of EVs will require development of a dramatically new battery chemistry that has the potential for higher energy densities than the Li ion,so-called“beyond Li ion”.This belief has stimulated extremely active research over the past decade into alternative battery chemistries that could potentially alleviate the“range anxiety”in an EV.Examples are Li?air,2 Li?S,3Zn?air4(and Al?air and Mg?air),the Mg ion,or other multivalent intercalation ions.5Li ion batteries with dramati-cally di?erent electrodes and electrolytes(e.g.,Li metal or Li/Si anodes,high-voltage cathodes,solid-state electrolytes)are also generally considered in the beyond Li ion category.6However, each new battery chemistry has its own distinct technical challenges,and it is at present unclear if or when any of these will mature into a useful technology.

Many of these new potential batteries involve poorly studied redox reactions.Thus,fundamental physical chemistry studies are generally the?rst order of business,and The Journal of Physical Chemistry Letters has been in the forefront of this active ?eld.For example,the emerging beyond Li ion?eld has contributed>10%of all articles published to date in JPC Lett., and it has contributed1/3of the15most cited papers in this journal.This issue of JPC Lett.includes three Perspectives devoted to aspects of beyond Li ion batteries.

Because traditional Li ion batteries use?ammable non-aqueous liquid electrolytes,there is always a residual safety issue in their use.In fact,a signi?cant fraction of the Li ion pack cost is in the battery management system to redundantly minimize the risk of?re/smoke.While this risk is quite small,the consequences with large-format Li ion battery packs can be catastrophic,for example,Tesla?res,Dreamliner,and so forth. Replacing the liquid electrolyte with a solid-state electrolyte would remove even this minimal risk.In addition,the possibility of using higher-capacity Li metal as the anode (instead of LiC6)and high-voltage cathodes(because of the higher electrochemical window in the solid-state electrolytes) suggests that all solid-state batteries also have the potential to provide higher energy densities than the traditional Li ion.In this issue of JPC Lett.,Thangadurai et al.discuss in detail a family of one of the most promising solid-state Li+-conducting solid-state electrolytes,Li-rich,garnet-type metal oxides (Thangadurai,V.;et al.J.Phys.Chem.Lett.2015,6,292?299).Some of these(e.g.,cubic Li7La3Zr2O12)have extremely appealing properties for the electrolyte in an all-solid-state battery:high Li+conductivity of~10?3S cm?1at room temperature with negligible electronic conductivity,chemical stability to Li metal,and very high electrochemical windows to ~6V versus Li/Li+.What has not yet been solved in solid-state batteries based on these or any other solid-state electrolytes are impedance issues related to the interfaces with the electrodes, and this limits the power density of current solid-state batteries. While chemical and morphological stability issues at the interfaces undoubtedly now play a role in the interface impedance,it is still unclear whether there are also fundamental charge-transport issues at the interfaces as well,for example, higher barriers for Li ionization and/or ion transport across the interface or the ionic equivalent of a Schottky barrier caused by the ionic space charge at the interface.

There has been intense research activity into nonaqueous Li?air(or Li?O2)and Li?S batteries because their theoretical energy densities are higher than that of the Li ion.2,3In fact, Li?air has a theoretical gravimetric energy density that rivals that of gasoline.However,electrolyte stability and charge-transport issues of the active species in the electrodes have not yet been satisfactorily solved for these batteries.Both batteries use ether-based electrolytes rather than the typical organic carbonate-based electrolytes used in Li ion batteries.Another issue for Li?S is that there are several soluble polysul?de intermediates in the charge transfer to the?nal product Li2S, forming a shuttle between the anode and cathode,and this decreases the coulombic e?ciency(and cycle lifetime)of this battery.3In this issue of JPC Lett.,Yang et al.discuss very recent research demonstrating that using elemental Se instead of O2or S to form a high volumetric energy density Li?Se battery reduces some of the technical challenges associated with Li?O2

Published:January15,2015

?2015American Chemical Society300DOI:10.1021/jz502665r

J.Phys.Chem.Lett.2015,6,300?301

and Li?S batteries(Yang,C.-P.;et al.J.Phys.Chem.Lett.2015,

6,256?266).These include much higher electrical conductivity

of the elemental Se in the anode and fewer electrolyte stability

challenges.With carbonate-based electrolytes,Li?Se forms

nominally insoluble polyselenide intermediates,so that

imbedding the elemental Se in mesoporous C as the anode

greatly reduces the destructive shuttle e?ect of polyselenides.

The major drawback to a Li?Se battery is cost because Se is an

expensive,low-abundant element.

In the third Perspective in this issue of JPC Lett.,Cheng et al.

describe a novel way to screen for desirable properties of

battery materials using high-throughput computational screen-

ing(Cheng,L.;et al.J.Phys.Chem.Lett.2015,6,283?291).

They discuss how quantum chemical calculations of redox

potentials,solubility,and chemical stability can be used

hierarchically to screen and identify potential molecules for

speci?c electrochemical storage applications.When combined

with appropriate chemical synthesis and testing,this forms a

genomic process in discovering new materials for energy

storage application.The authors demonstrate the application of

this procedure for~1400potential organic molecules for

nonaqueous redox?ow batteries.Such genomes will become

even more powerful when they can also integrate with the

larger world of existent chemical information already present

on the web,that is,by also incorporating“big data”.

Alan Luntz*

SUNCAT,SLAC National Accelerator Laboratory,2575

Sand Hill Road,Menlo Park,California94025,United

States

■AUTHOR INFORMATION

Corresponding Author

*E-mail:acluntz@https://www.doczj.com/doc/3713204668.html,.

■REFERENCES

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Storage with Renewable Electricity Generation.NREL Report No.TP-

6A2-47187;National Renewable Energy Laboratory:Golden,CO,

2010;pp1?61.

(2)Luntz,A.C.;McCloskey,B.D.Nonaqueous Li?Air Batteries:A

Status Report.Chem.Rev.2014,114,11721?11750.

(3)Manthiram, A.;Fu,Y.;Chung,S.-H.;Zu, C.;Su,Y.-S.

Rechargeable Lithium?Sulfur Batteries.Chem.Rev.2014,114,

11751?11787.

(4)Li,Y.;Dai,H.Recent Advances in Zinc?Air Batteries.Chem.Soc.

Rev.2014,43,5257?5275.

(5)Muldoon,J.;Bucur,C.B.;Gregory,T.Quest for Nonaqueous

Multivalent Secondary Batteries:Magnesium and Beyond.Chem.Rev.

2014,114,11683?11720.

(6)Manthiram, A.Materials Challenges and Opportunities of

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301

DOI:10.1021/jz502665r

J.Phys.Chem.Lett.2015,6,300?301

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