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Anapplicationoflithiumcobaltnickelmanganeseoxideto

Available online at https://www.wendangku.net/doc/df16289125.html, Journal of Power Sources174(2007)

813–817

Short communication

An application of lithium cobalt nickel manganese oxide to

high-power and high-energy density lithium-ion batteries

Hiroshi Yoshizawa a,b,Tsutomu Ohzuku b,?

a Technology Development Center,Matsushita Battery Industrial Co.Ltd.,1-1Matsushita-cho,

Moriguchi City,Osaka570-8511,Japan

b Department of Applied Chemistry,Graduate School of Engineering,Osaka City University(OCU),

Sugimoto3-3-138,Sumiyoshi,Osaka558-8585,Japan

Available online28June2007

Abstract

Evolved gas analysis(EGA)by mass spectroscopy(MS)was carried out for the pyrolysis of Li1?x Co1/3Ni1/3Mn1/3O2(185mAh g?1of charge capacity)and the results were compared with that of Li1?x CoO2(140mAh g?1).Electrochemically prepared Li1?x Co1/3Ni1/3Mn1/3O2clearly shows that O2evolution begins at much higher temperature than Li1?x CoO2,suggesting that Li1?x Co1/3Ni1/3Mn1/3O2is superior to LiCoO2with respect to thermal stability.High-temperature XRD measurements of charged LiCo1/3Ni1/3Mn1/3O2-electrodes at4.45V were also carried out and shown that the decomposition product by heating was identi?ed as a cubic spinel consisting of cobalt,nickel,and manganese.This indicates that phase change from a layered to spinel-framework structure plays a crucial role in the suppression of oxygen evolution from the solid matrix.In order to show practicability of the new material,lithium-ion batteries with graphite-negative electrodes are fabricated and examined in the R18650-hardware. The new lithium-ion batteries show high rate discharge performances,excellent cycle life,and safety together with high-energy density.

Keywords:Lithium cobalt nickel manganese oxide;EGA;Lithium-ion batteries

1.Introduction

During the past15years,increasing demands towards the high-energy density batteries stimulate material research on lithium insertion materials[1–3].Fig.1shows record on energy density of R18650(18mm of diameter,65.0mm of height)developed at Matsushita Battery Industrial Co.Ltd., Japan.Lithium-ion batteries consisting of LiCoO2and graphite approach500Wh dm?3in volumetric energy density in2002, i.e.,HG1.8Ah,A2.0Ah,and C2.2Ah.The volumetric energy density of500Wh dm?3is one of the critical values on LiCoO2 with graphite when we provide the batteries commercially with high-rate capability and long cycle life together with safety even in an abused use.In order to cope with a critical value of 500Wh dm?3,positive-electrode material of LiCoO2has been improved by doping magnesium or another element in LiCoO2 [4],resulting in energy densities more than500Wh dm?3for ?Corresponding author.

E-mail address:ohzuku@a-chem.eng.osaka-cu.ac.jp(T.Ohzuku).high-energy density type R18650,i.e.,D2.4Ah and E2.6Ah for the high-energy type and CC2.0Ah for a high-power type in Fig.1.However,high-energy and high-power type lithium-ion batteries are hard to design unless material innovation can be done.

Lithium nickel manganese oxides with or without cobalt have been investigated as possible alternatives to LiCoO2dur-ing the past6years in our research group[5–11].In previous papers[12,13],we have reported the cell performance on prismatic lithium-ion batteries of LiCo1/3Ni1/3Mn1/3O2with graphite together with some results on safety inspection by DSC and ARC.For high-power applications of lithium-ion batter-ies,such as hybrid electric vehicles or power tools,thermal behaviors associated with thermal runway[14,15]are extremely important in evaluating electrode materials in addition to elec-trochemical performance and materials economy.In this paper, we report the thermal behaviors of electrochemically charged LiCo1/3Ni1/3Mn1/3O2and discuss whether or not the lithium insertion material of lithium cobalt nickel manganese oxide is a suitable positive-electrode material for such practical applica-tions.

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813–817

Fig.1.Record on volumetric energy density of cylindrical lithium-ion batteries (R18650)developed at Matsushita Battery Industrial Co.Ltd.,Japan.Upper group indicates high-energy density type and lower group indicates high-power type.Lithium-ion batteries called HG1.8Ah,A2.0Ah,and C2.2Ah consist of LiCoO2and graphite.Batteries called CC2.0Ah,D2.4Ah,and E2.6Ah consist of improved LiCoO2and graphite.New batteries called CE2.3Ah and DA2.5Ah are designed for high-energy and high-power applications(see in text).

2.Experimental

Methods to prepare LiCo1/3Ni1/3Mn1/3O2,electrodes,or cells are the same as described in a previous paper[12].The pre-pared sample was characterized by XRD(X’Pert,Philips)and BET surface area.Morphology of particles was observed by scanning electron microscope(S-4500Hitachi Co.Ltd.,Japan). Evolved gas analysis by mass spectroscopy(EGA/MS)was per-formed using Agilent Technologies6890N GC and MS-5973N MS combined with pyrolyzer(PY-2020iD,FFRONTIER LAB). Helium was used as a carrier gas at a?ow rate of1cm3min?1. About5mg of the samples was precisely weighted and put in the chamber of pyrolyzer.Pyrolysis temperature was scanned from40?C to700?C at a rate of10?C min?1and then kept at 700?C for14min.Generated gas by pyrolysis was introduced into MS via a tube column maintained at300?C.Thermal stabil-ity tests on positive electrodes,so-called hot-pot tests,were also performed to examine whether or not thermal decomposition of electrode materials releasing oxygen relates to the thermal run-away.For the tests,the positive electrodes were taken out from charged cells and heated in the enclosed cylindrical can made of nickel-plated steel to300?C at a rate of5?C min?1.Other sets of experimental conditions are given in the following Section.

3.Results and discussion

Prepared sample of LiCo1/3Ni1/3Mn1/3O2was characterized by XRD.Crystal structure was identi?ed as a layered struc-ture(a=2.864?A and c=14.243?A in hexagonal setting).The calculated density was4.75g cm?3.Morphology of particles observed by SEM is shown in Fig.2.An average diame-ter of secondary particles is about10?m with small primary particles less than1?m in diameter.Particles crystallize well and nonporous body with smooth crystal surface is seen

Fig.2.Particle morphology of LiCo1/3Ni1/3Mn1/3O2observed by SEM. Fig.2.BET surface area is0.40m2g?1.These characters of the particles are not signi?cantly different from current LiCoO2.Fig.3(a)shows the charge and discharge curves of a Li/LiCo1/3Ni1/3Mn1/3O2cell operated at a rate of0.26mA cm?2 in voltage of3.0–4.45V at20?C.The electrolyte used is1.25M LiPF6dissolved in ethylene carbonate(EC)/ethyl methyl car-bonate(EMC)(1/3by volume).The charge and discharge curves of a Li/LiCoO2cell are also shown in Fig.3(b).The cell was operated at0.26mA cm?2in voltage of3.0–4.2V.As seen in Fig.3,LiCo1/3Ni1/3Mn1/3O2shows rechargeable capacity of 173mAh g?1with an average voltage of3.85V while LiCoO2 shows rechargeable capacity of142mAh g?1with an average voltage of about3.9V.

Fig.4shows the results on so-called hot-pot tests for electrochemically charged LiCo1/3Ni1/3Mn1/3O2-and LiCoO2-positive electrodes.In order to prepare the samples for hot-pot tests,LiCo1/3Ni1/3Mn1/3O2or LiCoO2electrode was charged in lithium-ion batteries with graphite-negative electrode.Onset temperature at which temperature on sample holder deviates from that in an oven due to heat generation from the

charged Fig.3.Charge and discharge curves of(a)Li/LiCo1/3Ni1/3Mn1/3O2and(b) Li/LiCoO2cells operated in voltages of3.0–4.45V and3.0–4.2V,respectively, at20?C.

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Fig.4.Results on so-called hot-pot tests for charged LiCo1/3Ni1/3Mn1/3O2-and LiCoO2-positive electrodes prepared at several charge-end voltages in lithium-ion batteries with graphite-negative electrode:(a)Li1?x Co1/3Ni1/3Mn1/3O2 charged at4.4V,(b)Li1?x Co1/3Ni1/3Mn1/3O2charged at4.7V,(c)Li1?x CoO2 charged at4.2V,and(d)Li1?x CoO2charged at4.7V.

LiCo1/3Ni1/3Mn1/3O2at4.4V is about230?C.Onset temper-ature shifts to lower temperature when the sample is prepared at high voltage of4.7V.Onset temperature for charged LiCoO2 at4.2V in lithium-ion batteries is about210?C,which is ca. 20?C lower temperature than that for LiCo1/3Ni1/3Mn1/3O2. In other words,LiCo1/3Ni1/3Mn1/3O2is thermally more sta-ble than LiCoO2when we compare thermal behavior of highly charged state of LiCo1/3Ni1/3Mn1/3O2at 4.4V(ca. 175mAh g?1of charge capacity)with that of LiCoO2at4.2V (ca.150mAh g?1).

Fig.5shows the EGA/MS results on charged LiCo1/3Ni1/3Mn1/3O2(185mAh g?1of charge capacity) and LiCoO2(140mAh g?1).To examine intrinsic thermal

behaviors of these materials,Li1?x Co1/3Ni1/3Mn1/3O2

and

Fig.5.The O2-gas signals obtained by MS(31.7–32.7in m/z)as a function of heating temperature for charged(a)LiCo1/3Ni1/3Mn1/3O2(185mAh g?1of charge capacity)and(b)LiCoO2(140mAh g?1of charge capacity).The samples were electrochemically prepared without the addition of carbon and organic binders.Li1?x CoO2were prepared by the electrochemical oxidation in lithium non-aqueous cells operated at8mA g?1with no carbon and organic binder.The cells used are2016-coin hardware. The MS signals of31.7–32.7in m/z corresponding to O2are illustrated in Fig.5.Charged samples were washed with EMC and dried in vacuum before EGA/MS analysis.Oxygen is detected at temperature below200?C and two humps at ca. 240and280?C are observed for Li1?x CoO2(140mAh g?1). Two humps are also observed for Li1?x Co1/3Ni1/3Mn1/3O2 (185mAh g?1).Their temperatures are ca.260?C and480?C, which are higher temperatures than those observed for Li1?x CoO2(140mAh g?1).As can be clearly seen in Fig.5, oxygen gas evolution from Li1?x Co1/3Ni1/3Mn1/3O2by heating is suppressed remarkably compared with that from Li1?x CoO2 in spite of highly charged state of Li1?x Co1/3Ni1/3Mn1/3O2, indicating that LiCo1/3Ni1/3Mn1/3O2is higher thermal stability than LiCoO2.

In order to identify the decomposition product of charged LiCo1/3Ni1/3Mn1/3O2electrode,high-temperature XRD measurements were carried out.Fig.6shows XRD patterns of decomposition products obtained by heat-ing the charged LiCo1/3Ni1/3Mn1/3O2-electrode at400?C. Li1?x Co1/3Ni1/3Mn1/3O2was prepared by charging lithium cells of LiCo1/3Ni1/3Mn1/3O2at a rate of0.26mA cm?2to charge-end voltage of4.45V.Decomposition product of cobalt nickel manganese hydroxide,used to prepare LiCo1/3Ni1/3Mn1/3O2, by heating at600?C is also shown in Fig.6,which is identi?ed as cubic spinel having a=ca.8.26?A.As seen in Fig.6,decom-position product of charged LiCo1/3Ni1/3Mn1/3O2is identi?ed as a cubic spinel.Although the ionic distribution of lithium and transition metals in a cubic close-packed oxygen array is not known yet,phase change from a layered to spinel-framework structure due to the mobile cation plays an important role on the suppression of active oxygen gas evolution by heating,as has been discussed by Delmas’s research group[16,17]for

lithium Fig.6.High-temperature XRD pattern on(a)the decomposition products observed by heating the charged LiCo1/3Ni1/3Mn1/3O2(charged at4.45V)at 400?C.Decomposition product obtained by heating a precursor of cobalt nickel manganese hydroxide at600?C is also shown in(b).The precursor is used to prepare LiCo1/3Ni1/3Mn1/3O2.XRD pattern(b)is observed at room temperature.

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Fig.7.Rate-capability tests on the lithium-ion battery(R18650;2.3Ah of nominal capacity)consisting of new positive electrode and graphite-negative electrode.The battery was discharged at(a)430mA,(b)2150mA,and(c) 4300mA at20?C.The battery was charged at constant current of1500mA up to4.2V followed by charging at constant voltage of4.2V until charging current reaches below110mA.

nickel oxide derivatives.Mobile cations may be manganese ions because the thermal behaviors stated above are not observed for LiCoO2or more generally LiCo x Ni1?x O2[18].

In order to bridge basic researches on lithium insertion materials and industrial technologies,basic research results on lithium cobalt nickel manganese oxide have been applied to the design for advanced lithium-ion batteries.After improving and adjusting several parametric factors to fabricate practical lithium-ion batteries,we have made lithium-ion batteries con-sisting of graphite and novel lithium insertion material.Fig.7 shows the results of rate-capability tests on the cylindrical lithium-ion batteries R18650having2.3Ah capacity,called CE2.3Ah in Fig.1.The batteries are charged at constant current of1500mA to charge-end voltage of4.2V and then at con-stant voltage of4.2V until the current reaches below110mA at 20?C,so-called CCCV.The batteries are discharged to2.5V

at a rate of(a)430mA,(b)2150mA,and(c)4300mA

Fig.8.Heating tests on the lithium-ion battery of new lithium insertion material and graphite(R18650-CE2.3Ah):(a)temperature on battery surface and(b) temperature in an oven.Heating rate is5?C min?1up to150or170?C.20?C.As can be seen in Fig.7,lithium-ion batteries show high rate discharge performance.Fig.8shows the results on heat-ing tests of new R18650lithium-ion batteries for high-power and high-energy density applications.After lithium-ion batter-ies were charged at CCCV of1500mA to4.2V,the batteries were heated up to150?C or170?C at a rate of5?C min?1 and kept at that temperature in an oven.The lithium-ion batter-ies do not show rapid increase in temperature associated with thermal runaway even when the batteries are heated at170?C [19].

4.Concluding remarks

In this paper,we have shown new lithium-ion batteries by applying novel lithium insertion material of lithium cobalt nickel manganese oxide.The batteries show high-power and high-energy densities with excellent cycle life and safety.Because thermal behaviors of the new batteries are much milder than that of current lithium-ion batteries of LiCoO2,safety devices of PTC could be removed in designing lithium-ion batteries[20]. Actually,this type of new lithium-ion batteries for high-power application has been produced since late autumn in2004,called CE2.3Ah in Fig.1,and improved energy density in2005,called DA2.5Ah showing more than500Wh dm?3in energy density even for high-power applications.As were brie?y described above,this type of lithium-ion battery is one of the promising lithium-ion batteries for high-power applications,such as hybrid electric vehicles and power tools.

Acknowledgement

The present work was partially supported by a grant-in-aid from the Osaka City University(OCU)Science Foundation. References

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