A review of advanced and practical lithium battery materials
Rotem Marom,*S.Francis Amalraj,Nicole Leifer,David Jacob and Doron Aurbach
Received 3rd December 2010,Accepted 31st January 2011DOI:10.1039/c0jm04225k
Prented herein is a discussion of the forefront in rearch and development of advanced electrode materials and electrolyte solutions for the next generation of lithium ion batteries.The main challenge of the field today is in meeting the demands necessary to make the electric vehicle fully commercially viable.This requires high energy and power densities with no compromi in safety.Three families of advanced cathode materials (the limiting factor for energy density in the Li battery systems)are discusd in detail:LiMn 1.5Ni 0.5O 4high voltage spinel compounds,Li 2MnO 3–LiMO 2high capacity composite layered compounds,and LiMPO 4,where M ¼Fe,Mn.Graphite,Si,Li x TO y ,and MO (conversion reactions)are discusd as anode materials.The electrolyte is a key component that determines the ability to u high voltage cathodes and low voltage anodes in the same system.
Electrode–solution interactions and passivation phenomena on both electrodes in Li-ion batteries also play significant roles in determining stability,cycle life and safety features.This prentation is aimed at providing an overall picture of the road map necessary for the future development of advanced high en
ergy density Li-ion batteries for EV applications.
Introduction
One of the greatest challenges of modern society is to stabilize a consistent energy supply that will meet our growing energy demands.A consideration of the facts at hand related to the energy sources on earth reveals that we are not encountering an energy crisis related to a shortage in total resources.For instance
the earth’s crust contains enough coal for the production of electricity for hundreds of years.1However the continued unbridled usage of this resource as it is currently employed may potentially bring about catastrophic climatological effects.As far as the availability of crude oil,however,it in fact appears that we are already beyond ‘peak’production.2As a result,increasing oil shortages in the near future em inevitable.Therefore it is of critical importance to considerably decrea our u of oil for propulsion by developing effective electric vehicles (EVs).EV applications require high energy density energy storage devices that can enable a reasonable driving range between
Department of Chemistry,Bar-Ilan University,Ramat-Gan,52900,Israel;Web:www.ch.biu.ac.il/pe
ople/aurbach.E-mail:rotem.marom@live.biu.ac.il;
aurbach@mail.biu.ac.il
Rotem Marom
Rotem Marom received her BS degree in organic chemistry (2005)and MS degree in poly-mer chemistry (2007)from Bar-Ilan University,Ramat Gan,Israel.She started a PhD in electrochemistry under the supervision of Prof.D.Aurbach in 2010.She is currently con-ducting rearch on a variety of lithium ion battery materials for electric vehicles,with a focus on electrolyte solutions,salts and
additives.
S :Francis Amalraj
Francis Amalraj hails from Tamil Nadu,India.He received his MSc in Applied Chemistry from Anna University.He then carried out his doctoral studies at National Chemical Laboratory,Pune and obtained his PhD in Chemistry from Pune University (2008).He is currently a postdoctoral fellow in Prof.Doron Aurbach’s group at Bar-Ilan University,Israel.His current rearch interest focus on the synthesis,electrochemical and transport properties of high ener-getic electrode materials for energy conversion and storage systems.
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Cite this:DOI:10.1039/c0jm04225k /materials
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charges and maintain acceptable speeds.3Other important requirements are high power density and acceptable safety features.The energy storage field faces a cond critical chal-lenge:namely,the development of rechargeable systems for load leveling applications (e.g.storing solar and wind energy,and reducing the massive wasted electricity from conventional fossil fuel combustion plants).4Here the main requirements are a very prolonged cycle life,components (i.e.,relevant elements)abun-dant in high quantities in the earth’s crust,and environmentally friendly systems.Since it is not clear whether Li-ion battery technology can contribute significantly to this application,battery-centered solutions for this application are not discusd
herein.In fact,even for electrical propulsion,the non-petroleum power source with the highest energy density is the H 2/O 2fuel cell (FC).5However,despite impressive developments in recent years in the field,there are intrinsic problems related to electrocatalysis in the FCs and the storage of hydroge
n 6that will need many years of R&D to solve.Hence,for the foreeable future,rechargeable batteries appear to be the most practically viable power source for EVs.Among the available battery technologies to date,only Li-ion batteries may posss the power and energy densities necessary for EV applications.
The commonly ud Li-ion batteries that power almost all portable electronic equipment today are comprid of a graphite anode and a LiCoO 2cathode (3.6V system)and can reach a practical energy density of 150W h kg À1in single cells.This battery technology is not very uful for EV application due to its limited cycle life (especially at elevated temperatures)and prob-lematic safety features (especially for large,multi-cell modules).7While there are ongoing developments in the hybrid EV field,including practical ones in which only part of the propulsion of the car is driven by an electrical motor and batteries,8the main goal of the battery community is to be able to develop full EV applications.This necessitates the development of Li-ion batteries with much higher energy densities compared to the practical state-of-the-art.The biggest challenge is that Li-ion batteries are complicated devices who components never reach thermodynamic stability.The surface chemistry that occurs within the systems is very complicated,as described briefly below,and continues to be the main factor that determines their performance.
9
Nicole Leifer Nicole Leifer received a BS degree in chemistry from MIT in 1998.After teaching high school chemistry and physics for veral years at Stuyvesant High School in New York City,she began work towards her PhD in solid state physics from the City University of New York Grad-uate C
enter.Her rearch con-sisted primarily of employing solid state NMR in the study of lithium ion electrode materials
and electrode surface
phenomena with Prof.Green-baum at Hunter College and
Prof.Grey at Stony Brook University.After completing her PhD she joined Prof.Doron Aurbach for a postdoctorate at Bar-Ilan University to continue work in lithium ion battery rearch.There she continues her work in using NMR to study lithium materials in addition to new forays into carbon materials’rearch for super-capacitor applications with a focus on enhancement of electro-chemical performance through the incorporation of carbon
nanotubes.
David Jacob David Jacob earned a BSc from Amravati University in 1998,an MSc from Pune University in 2000,and completed his PhD at Bar-Ilan University in 2007under the tutelage of Professor Aharon Gedanken.As part of his PhD rearch,he developed novel methods of synthesizing metal fluoride nano-material structures in ionic liquids.Upon finishing his PhD he joined Prof.Doron Aurbach’s lithium ion
battery group at Bar-Ilan in
2007as a post-doctorate and during that time developed new
formulations of electrolyte solutions for Li-ion batteries.He has a great interest in nanotechnology and as of 2011,has become the CEO of IsraZion Ltd.,a company dedicated to the manufacturing of novel
nano-materials.
Doron Aurbach Dr Doron Aurbach is a full Professor in the Department of Chemistry at Bar-Ilan Univer-sity (BIU)in Ramat Gan,Israel and a nate member at BIU since 1996.He chaired the chemistry department there during the years 2001–2005.He is also the chairman of the Israeli Labs
Accreditation Authority.He founded the elec-trochemistry group at BIU at the end of 1985.His group
conducts rearch in the
following fields:Li ion batteries for electric vehicles and for other
portable us (new cathodes,anodes,electrolyte solutions,elec-trodes–solution interactions,practical systems),rechargeable magnesium batteries,electronically conducting polymers,super-capacitors,engineering of new carbonaceous materials,develop-ment of devices for storage and conversion of sustainable energy (solar,wind)nsors and water desalination.The group currently collaborates with veral prominent rearch groups in Europe and the US and with veral commercial companies in Israel and abroad.He is also a fellow of the ECS and ISE as well as an associate editor of Electrochemical and Solid State Letters and the Journal of Solid State Electrochemistry.Prof.Aurbach has more than 350journals publications.
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All electrodes,excluding 1.5V systems such as LiTiO x anodes,are surface-film controlled (SFC)systems.At the anode side,all conventional electrolyte systems can be reduced in the prence of Li ions below 1.5V,thus forming insoluble Li-ion salts that compri a passivating surface layer of particles referred to as the solid electrolyte interpha (SEI).10The cathode side is less trivial.Alkyl carbonates can be oxidized at potentials below 4V.11The reactions are inhibited on the passivated aluminium current collectors (Al CC)and on the composite cathodes.There is a rich surface chemistry on the cathode surface as well.In their lithiated state,nucleophilic oxygen anions in the surface layer of the cathode particles attack electrophilic RO(CO)OR solvents,forming different combinations of surface components (e.g.ROCO 2Li,ROCO 2M,ROLi,ROM etc.)depending on the electrolytes ud.12The polymerization of solvent molecules such as EC by cationic stimulation results in the formation of poly-carbonates.13The dissolution of transition metal cations forms surface inactive Li x MO y phas.14Their precipitation on the anode side destroys the passivation of the negative electrodes.15Red-ox reactions with solution species form inactive LiMO y with the transition metal M at a lower oxidation state.14LiMO y compounds are spontaneously delithiated in air due to reactions with CO 2.16Acid–ba reactions occur in the LiPF 6solutions (trace HF,water)that are commonly ud in Li-ion batteries.Finally,LiCoO 2itlf has a rich surface chemistry that influences its performance:平面培训设计
4LiCo III O 2 !Co IV O 2þCo II Co III 2O 4þ2Li 2O !4HF
4LiF þ2H 2O Co III compounds oxidize alkyl carbonates;CO 2is one of the products,Co III /Co II /Co 2+dissolution.14
Interestingly,this process ems to be lf-limiting,as the prence of Co 2+ions in solution itlf stabilizes the LiCoO 2electrodes,17However,Co metal in turn appears to deposit on the negative electrodes,destroying their passivation.
Hence the performance of many types of electrodes depends on their surface chemistry.Unfortunately surface studies provide more ambiguous results than bulk studies,therefore there are still many open questions related to the surface chemistry of Li-ion battery systems.
mean taylor swiftIt is for the reasons that proper R&D of advanced materials for Li-ion batteries has to include bulk structural and perfor-mance studies,electrode–solution interactions,and possible reflections between the anode and cathode.The studies require the u of the most advanced electrochemical,18structural (XRD,HR microscopy),spectroscopic and surface nsitive analytical techniques (SS NMR,19FTIR,20XPS,21Raman,22X-ray bad spectroscopies 23).This prentation provides a review of the forefront of the study of advanced materials—electrolyte systems,current col
lectors,anode materials,and finally advanced cathodes materials ud in Li-ion batteries,with the emphasis on contributions from the authors’group.
Experimental
Many of the materials reviewed were studied in this laboratory,therefore the experimental details have been provided as follows.The LiMO 2compounds studied were prepared via lf-combus-tion reactions (SCRs).24Li[MnNiCo]O 2and Li 2MnO 3$Li/MnNiCo]O 2materials were produced in nano-and
黑月亮submicrometric particles both produced by SCR with different annealing stages (700 C for 1hour in air,900 C or 1000 C for 22hours in air,respectively).LiMn 1.5Ni 0.5O 4spinel particles were also synthesized using SCR.Li 4T 5O 12nanoparticles were obtained from NEI Inc.,USA.Graphitic material was obtained from Superior Graphite (USA),Timcal (Switzerland),and Conoco-Philips.LiMn 0.8Fe 0.2PO 4was obtained from HPL Switzerland.Standard electrolyte solutions (alkyl carbonates/LiPF 6),ready to u,were obtained from UBE,Japan.Ionic liquids were obtained from Merck KGaA (Germany and Toyo Gosie Ltd.,(Japan)).
The surface chemistry of the various electrodes was charac-terized by the following techniques:Fouri
er transform infrared (FTIR)spectroscopy using a Magna 860Spectrometer from Nicolet Inc.,placed in a homemade glove box purged with H 2O and CO 2(Balson Inc.air purification system)and carried out in diffu reflectance mode;high-resolution transmission electron microscopy (HR-TEM)and scanning electron microscopy (SEM),using a JEOL-JEM-2011(200kV)and JEOL-JSM-7000F electron microscopes,respectively,both equipped with an energy dispersive X-ray microanalysis system from Oxford Inc.;X-ray photoelectron spectroscopy (XPS)using an HX Axis spectrom-eter from Kratos,Inc.(England)with monochromic Al K a (1486.6eV)X-ray beam radiation;solid state 7Li magic angle spinning (MAS)NMR performed at 194.34MHz on a Bruker Avance 500MHz spectrometer in 3.2mm rotors at spinning speeds of 18–22kHz;single pul and rotor synchronized Hahn echo quences were ud,and the spectra were referenced to 1M LiCl at 0ppm;MicroRaman spectroscopy with a spectrometer
from Jobin-Yvon Inc.,France.We also ud M €o
ssbauer spec-troscopy for studying the stability of LiMPO 4compounds (conventional constant-acceleration spectrometer,room temperature,50mC:57Co:Rh source,the absorbers were put in Perspex holders.In situ AFM measurements were carried out using the system described in ref.25.
神探夏洛克第二季02The following electrochemical measurements were conducted.Composite electrodes were prepared by spreading slurries comprising the active mass,carbon powder and poly-vinylidene difluoride (PVdF)binder (ratio of 75%:15%:10%by weight,mixed into N -methyl pyrrolidone (NMP),and deposited onto aluminium foil current collectors,followed by drying in a vacuum oven.The average load was around 2.5mg active mass per cm 2.The electrodes were tested in two-electrode,coin-type cells (Model 2032from NRC Canada)with Li foil rving as the counter electrode,and various electrolyte solutions.Computer-ized multi-channel battery analyzers from Maccor Inc.(USA)and Arbin Inc.were ud for galvanostatic measurements (voltage vs.time/capacity,measured at constant currents).
Results and discussion
Our road map for materials development
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Fig.1indicates a suggested road map for the direction of Li-ion rearch.The axes are voltage and capacity,and a variety of electrode materials are marked therein according to their respective values.As is clear,the main limiting factor is the cathode material (in voltage and capacity).The electrode mate-rials currently ud in today’s practical batteries allow for
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a nominal voltage of below 4V.The lower limit of the electro-chemical window of the currently ud electrolyte solutions (alkyl carbonates/LiPF 6)is approximately 1.5V vs.Li 26(e later discussion about the passivation phenomena that allow for the operation of lower voltage electrodes,such as Li and Li–graphite).The anodic limit of the electrochemical window of the alkyl carbonate/LiPF 6solutions has not been specifically determined but practical accepted values are between 4.2and 5V vs.Li 26(e further discussion).With some systems which will be discusd later,meta-stability up to 4.9V can be achieved in the standard electrolyte solutions.Electrolyte solutions
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The anodic stability limits of electrolyte solutions for Li-ion batteries (and tho of polar aprotic solutions in general)demand ongoing rearch in this subfield as well.It is hard to define the ont of oxidation reactions of nonaqueous electrolyte solutions becau the strongly depend on the level of purity,the prence of contaminants,and the types of electrodes ud.Alkyl carbonates are still the solutions of choice with little competition (except by ionic liquids,as discusd below)becau of the high oxidation state of their central carbon (+4).Within this class of compounds EC and DMC have th
导游证培训e highest anodic stability,due to their small alkyl groups.An additional benefit is that,as discusd above,all kinds of negative electrodes,Li,Li–graphite,Li–Si,etc.,develop excellent passivation in the solutions at low potentials.
The potentiodynamic behavior of polar aprotic solutions bad on alkyl carbonates and inert electrodes (Pt,glassy carbon,Au)shows an impressive anodic stability and an irreversible cathodic wave who ont is $1.5vs.Li,which does not appear in conquent cycles due to passivation of the anode surface by
the SEI.The ont of the oxidation reactions is not well defined (>4/5V vs.Li).An important discovery was the fact that in the prence of Li salts,EC,one of the most reactive alkyl carbonates (in terms of reduction),forms a variety of mi-organic Li-con-taining salts that rve as passivation agents on Li,Li–carbon,Li–Si,and inert metal electrodes polarized to low potentials.Fig.2and Scheme 1indicates the most significant reduction schemes for EC,as elucidated through spectroscopic measure-ments (FTIR,XPS,NMR,Raman).27–29It is important to note (as reflected in Scheme 1)that the nature of the Li salts prent greatly affects the electrode surface chemistry.When the pres-ence of the salt does not induce the formation of acidic species in solutions (e.g.,LiClO 4,LiN(SO 2CF 3)2),alkyl carbonates are reduced to ROCO 2Li and ROLi compounds,as prented in Fig. 2.In LiPF
6solutions acidic species are formed:LiPF 6decompos thermally to LiF and PF 5.The latter moiety is a Lewis acid which further reacts with any protic contaminants (e.g.unavoidably prent traces of water)to form HF.The prence of such acidic species in solution strongly affects the surface chemistry in two ways.One way is that PF 5interacts
with
Fig.1The road map for R&D of new electrode materials,compared to today’s state-of-the-art.The y and x axes are voltage and specific capacity,
respectively.
Fig.2A schematic prentation of the CV behavior of inert (Pt)elec-trodes in various families of polar aprotic solvents with Li salts.26
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the carbonyl group and channels the reduction process of EC to form ethylene di-alkoxide species along with more complicated alkoxy compounds such as binary and tertiary ethers,rather than Li-ethylene dicarbonates (e schemes in Fig.2);the other way is that HF reacts with ROLi and ROCO 2Li to form ROH,ROCO 2H (which further decompos to ROH and CO 2),and surface LiF.Other species formed from the reduction of EC are Li-oxalate and moieties with Li–C and C–F bonds (e Scheme 1).27–31
Efforts have been made to enhance the formation of the passivation layer (on graphite electrodes in particular)in the prence of the solutions through the u of surface-active additives such as vinylene carbonate (VC)and lithium bi-oxalato borate (LiBOB).27At this point there are hundreds of publica-tions and patents on various passivating agents,particularly for graphite electrodes;their further discussion is beyond the scope of this paper.Readers may instead be referred to the excellent review by Xu 32on this subject.yahang
Ionic liquids (ILs)have excellent qualities that could render them very relevant for u in advanced Li-ion batteries,including high anodic stability,low volatility and low flammability.Their main drawbacks are their high viscosities,problems in wetting particle pores in composite structures,and low ionic conductivity at low temperatures.Recent years have en increasing efforts to test ILs as solvents or additives in Li-ion battery systems.33
Fig.3shows the cyclic voltammetric respon (Pt working electrodes)of imidazolium-,piperidinium-,and pyrrolidinium-bad ILs with N(SO 2CF 3)2Àanions containing LiN(SO 2CF 3)2salt.34This figure reflects the very wide electrochemical window and impressive anodic stability (>5V)of piperidium-and pyr-rolidium-bad ILs.Imidazolium-bad IL solutions have a much lower cathodic stability than the above cyclic quaternary ammonium cation-bad IL solutions,as demonstrated in Fig.3.The cyclic voltammograms of veral common electrode mate-rials measured in IL-bad solutions are also included in the figure.It is clearly demonstrated that the Li,Li–Si,LiCoO 2,and
LiMn 1.5Ni 0.5O 4electrodes behave reversibly in piperidium-and pyrrolidium-bad ILs with N(SO 2CF 3)2Àand LiN(SO 2CF 3)2salts.This figure demonstrates the main advantage of the above IL systems:namely,the wide electrochemical window with exceptionally high anodic stability.It was dem
onstrated that aluminium electrodes are fully passivated in solutions bad on derivatives of pyrrolidium with a N(SO 2CF 3)2Àanion and LiN(SO 2CF 3)2.35Hence,in contrast to alkyl carbonate-bad solutions in which LiN(SO 2CF 3)2has limited ufulness as a salt due to the poor passivation of aluminium in its solutions in the above IL-bad systems,the u of N(SO 2CF 3)2Àas the anion doesn’t limit their anodic stability at all.In fact it was possible to demonstrate prototype graphite/LiMn 1.5Ni 0.5O 4and Li/L-iMn 1.5Ni 0.5O 4cells operating even at 60 C in
solutions
Scheme 1A reaction scheme for all possible reduction paths of EC that form passivating surface species (detected by FTIR,XPS,Raman,and SSNMR 28–31,49
).
Fig.3Steady-state CV respon of a Pt electrode in three IL solutions,as indicated.(See structure formulae prented therein.)The CV prentations include ints of steady-state CVs of four electrodes,as indicated:Li,Li–Si,LiCoO 2,and LiMn 1.5Ni 0.5O 4.34
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