CMPSITIN PRECURSR FR ALUMINUM-CNTAINING
LITHIUM TRANSITIN METAL XIDE AND PRCESS FR
PREPARATIN F THE SAME
FIELD F THE INVENTIN
The present inventin relates t a cmpsite precursr fr aluminum-cntaining lithium transitin metal xide and a prcess fr preparatin theref. Mre specifically, the present inventin relates t a cmpsite precursr cmprising a cre f lithium transitin metal xide and an alummum hydrxide-based precipitate layer cated n the surface f the cre, and a preparatin prcess f the cmpsite precursr by precipitatin reactin f an aluminum salt slutin and a base slutin t cat the lithium transitin metal xide, as a seed partide, in a water-based slurry r paste.
BACKGRUND F THE INVENTIN
In cmmercial rechargeable lithium batteries, lithiated transitin metal xides are emplyed as a cathde active material and these transitin metal xides include, fr example, materials f the layered crystal structure such as LiCi, Li(MniftNii/2)i. xCx2, r LiNii-xCx2, and materials f the spinel crystal structure such as lithium manganese xide spinel r lithium manganese-nickel xide spinel. Depending n the applicatin, certain prperties f these materials are f imprtance and such prperties can be mdified by prcessing, dping, surface treatment, cntrl f impurities, etc.
Sme f these materials, particularly where nly ne type f transitin metal is present, can be easily prepared by slid state reactin using simple transitin metal precursrs. Hwever, mre "cmplex" materials, particularly where tw r mre types f transitin metals are present, are difficult r impssible t prepare by simple slid state reactin, i.e. by mixing separate transitin metal precursrs. Instead, cmplex lithium transitin metal xides are generally prepared by reacting mixed precursrs, e.g., mixed hydrxides r mechanically allyed transitin metal xides, with a surce f lithium.
Mixed hydrxides are typically prepared by precipitatin reactin. Precipitatin f mixed hydrxides (fr example, the precipitatin f a flw f NaH with a flw f M-S4 under cntrlled pH) r mixed carbnates (fr example, the precipitatin f a flw f Na2CC3 with a flw f M-S/ allws precursrs f suitable mrphlgy t be achieved. A prblem is the level f impurities; especially, the remval f sulfur is difficult and expensive. The same prblems apply t the remval f sdium in the case f mixed carbnates.
Meanwhile, as ne methd fr mdificatin f lithium transitin metal xides, dping nas been widely investigated. The dping typically des nt exceed 5% by atms f dpant per transitin metal. Typical dpants are either inserted isstracturally int the existing crystal structure (e.g., Al-dped LiCa) r they frm a secndary phase, ften agglmerating at grain bundaries (e.g., Zr-dped LiCa).
In the dping apprach, aluminum is a general dpant. The benefît f aluminum-mdified lithium transitin metal xides has been widely investigated. Fr example, it is knwn that adding Al t the crystal structure f LiNii.xCx02 imprves safety and cycling stability. Fr example, Al-dped LiMn2-xLix04 spinel cycles mre
stably and als shws less disslutin f Mn, and Al-cated LiCa cycles mre stably at high vltage.
A prblem assciated with aluminum-mdifîed lithium transitin metal xides, i.e., Al-cntaining lithium transitin metal xides, is the preparatin prcess theref. In the case f cmplex lithium transitin metal xides, mixed precursrs wuld have t cntain aluminum; hwever, it is mre difficult t prepare Al-cntaining precursrs such as Al-dped mixed transitin metal hydrxide. Alternatively, lithium transitin metal xides culd be prepared by mixing raw materials with a surce f aluminum such as Alaa r A1(H)3. In this regard, it shuld be nted that Aks has lw reactivity and A1(H)3 is easily transfrmed t As at lw temperature. Therefre, the btained cathde is nnhmgeneusly dped s that the benefît f aluminum dping is nt fully utilized.
In a prcess fr preparatin f Al-dped materials, if a layer cntaining a reactive aluminum phase were t fully cver the surface f a subject partide such as lithium transitin metal xide, this wuld be advantageus. If this were pssible, the difîusin pathway wuld be shrt and the cntact area wuld be large s that an Al-dped material culd be achieved at relatively lw reactin temperature. As will be illustrated later, the present inventin disclses such cmpsite precursr fully cated with a reactive aluminum phase and a prcess fr preparatin f the cmpsite precursr.
Meanwhile, besides the Al dping apprach, an Al cating apprach is als knwn as a means t imprve prperties. In a cnvenţinal Al cating prcess, lithium transitin metal xide particles are dipped int an aluminum-cntaining slutin r gel, fllwed by drying and mild heat treatnent. As a result, the surface f lithium transitin
metal xide is cated by an aluminum xide-based phase. This phase separates the electrlyte frm the mre reactive bulk and prmises imprved prperties. Hwever, the cnvenţinal Al cating prcess has demerits as explained belw.
In the prir art Al cating prcess, lithium transitinal metal xides are dipped int A1P4 r tri-butyl aluminum disslved in ethanl. Prblems are the cst f raw materials and the use f rganic slvents that may căuşe the generatin f gas during reactin r drying prcedures. A further prblem is that nly a small amunt f Al can be cated n the lithium transitin metal xide. Lw slubility f A1P04 r tri-butyl aluminum limits the amunt f aluminum present in a layer frmed by dip-cating. Where an rganic slvent is used in large amunts t cmpensate fr the lw slubility, aluminum-cntaining particles frm, but fail t cver the lithium transitin metal xide. Generally, the cntact between the aluminum cmpund and lithium transitin metal xide after a drying prcedure is maintained mainly by physical adhesin and t a lesser extent by chemical bnds. Aecrdingly, althugh a thicker cating layer is made, it tends t disintegrate during drying.
As an alternative apprach, a partide cating prcess is als knwn in the art. In this prcess, cating is achieved by dipping lithium transitin metal xides int a slurry f fine particles. Alternatively, it is als pssible t apply a dry cating apprach. In this dry cating prcess, fine pwders, typically Alaa particles f sub-micrmeter size are mixed with lithium transitin metal xides. Hwever, the partide cating prcess has sme disadvantages, as fllws: (i) it is difficult t achieve a full cverage by fine particles; (ii) it is difficult t prevent agglmeratin f fine pwders, and the resulting agglmerates fail t efficiently cver the surface f lithium transitin metal xide; and (iii) the adhesin between fine particles and lithium transitin metal xide is pr s that the cating layers tend t peel ff during subsequent prcesses.
Therefre, imprved precursrs fr cathde active material and a methd t prepare such precursrs are needed. The imprved precursrs culd be characterized as lithium transitin metal xide with a unifrmly thick layer fully cvering the partide, the layer having gd mechanical cntact, cntaining alurninum and being practically free f impurities.
SUMMARY F THE INVENTIN
The bjects f the present inventin are t cmpletely slve the prblems described abve.
Specifically, an bject f the present inventin is t prvide a cmpsite precursr fr aluminum-cntaining lithium transitin metal xide as a cathde active material. The cmpsite precursr has an alurninum hydrxide-based precipitate layer f active alurninum phase n the surface f a lithium transitin metal xide cre and can be cnverted int an Al-dped lithium transitin metal xide by heat treatment.
Anther bject f the present inventin is t prvide a prcess f preparing the cmpsite precursr by precipitatin reactin f an alurninum salt slutin and base slutin. This precipitatin prcess has many advantages; fr example, impurities such as sulfur, sdium r chlride present in raw materials can be tlerated, and rganic slvents are nt used, and a fully cated, stable prduct can be btained.
A further bject f the present inventin is t prvide an aluminum-cntaining lithium transitin metal xide able t be prduced frm the cmpsite precursr. The alummum-cntaining lithium transitin metal xide can be applied t a cathde active material fr rechargeable lithium batteries.
In rder t accmplish these bjects, there is prvided in the present inventin
a cmpsite precursr fr aluminum-cntaining lithium transitin metal xide cmprising (a) a lithium transitin metal xide cre, and (b) an aluminum hydrxide-based precipitate layer f active aluminum phase cated n the surface f the lithium transitin metal xide cre, with the aluminum hydrxide-based precipitate cntaining a divalent anin. This cmpsite precursr is a nvei material nt knwn in the art t which the present inventin pertains.
In an embdiment f the present inventin, the aluminum hydrxide-based precipitate layer is lithium-aluminum-sulfate-hydrxide-hydrate. In this case, the divalent anin is sulfate. The sulfate present in the precipitate layer can be easily replaced by carbnate t allw the precipitate layer t be practically free f sulfur. Therefre, the aluminum hydrxide-based precipitate layer is preferably f lithium-aluminum-carbnate-hydrxide-hydrate. In this case, the divalent anin is carbnate.
The present inventin als prvides a prcess fr the preparatin f the cmpsite precursr, cmprising a step f carrying ut the precipitatin reactin f an aluminum salt slutin and base slutin with a lithium transitin metal xide as a seed partide dispersed in a water-based slurry r paste t fnn an aluminum hydrxide-based precipitate layer n the surface f lithium transitin metal xide partide.
In a preferable embdiment f the present inventin, after the precipitatin reactin, an in exchange reactin is further perfrmed t replace the sulfate present in the precipitate layer with carbnate by adding a carbnate slutin int the reactin system. Several experiments described in the present disclsure surprisingly shw that the in exchange reactin allws the precipitate layer t be practically free f sulfate.
Als, the present inventin prvides an aluminum-cntaining lithium transitin metal xide prduced by heat treatment f the cmpsite precursr as defined
abve. This aluminum-cntaining lithium transitin metal xide is suitable fr a cathde active material f lithium rechargeable battery, shwing mre excellent prperties than the prir art lithium transitin metal xide and Al-cated r Al-dped lithium transitin metal xides.
BRIEF DESCRIPTIN F THE DRAWINGS
FIG. l is the cmbinatin f tw X-ray diffractin pattenis in which the tp shws the precipitate after gentle drying and the bttm shws the lithium aluminum carbnate hydrxide hydrate btained after an in exchange reactin fllwed by gentle drying.
FIGS. 2 ~ 4 are FESEM micrgraphs f LiCC2 partide cated with litbium-aluminum-carbnate-hydrxide-hydrate after drying at ISC, prepared m Example 3.
FIG. 5 is a cmbinatin f tw graphs fr electrchemical cycling (C/5, 60°C), hi which the tp shws untreated LiCC and the bttm shws aluminum mdified carried ut ui Example 9.
DETAILED DESCRIPTIN F THE INVENTIN
The present inventin is illustrated belw in mre detail.
In the cmpsite precursr accrding t the present inventin, the thickness f the precipitate layer is nt particularly lirnited because it can be varied depending upn the aluminum cntent required fr an intended duminum-cntainhig lithium transitin metal xide. In an embdiment, the ttal amunt f aluminum in the precipitate layer is 0.5 t 5% by atms with respect t the ttal amunt f transitin metal in the cmplex precursr.
As has been mentined already, the aluminum hydrxide-based precipitate ayer is present as an active aluminum phase which is a thermdynamically stabilized jhase resistant t disslving even at high pH, and which can als be easily cnverted nt an Al-dped layer f lithium transitin metal xide by apprpriate heat treatment.
The lithium transitin metal xide as the cre f cmpsite precursr has a layered r spinel crystal structure, and includes, fr example, but is nt limited t LiC2, cbalt-rich Li(Mni/2Nii/2)i-xCx2, lithium manganese spinel such as LiMn2. xLix04 and dped lithium manganese spinel, lithium manganese-nickel spuiel such as Li(Mni.6Ni.4)C43 lithium manganese nickel xide such as LiMni/sNii/aCi/aa, r lithium nickel xide-based materials such as LiNi.8C.22 and LiNi.8C.i5A.s2 (A = Mn, Al, MgTi, etc.).
In the preparatin prcess f the cmpsite precursr accrding t the present inventin, the lithium transitin metal xide as a raw material can be tlerated t cntain unpurities such as sulfur, sdium, chlride, etc. which are highly undesirable in cmmercial lithium rechargeable batteries. Surprishigly, these impurities are remved frm the lithium transitin metal xide during the precipitatin reactin f the present inventin, which can be seen in Example 10 f the present disclsure. Accrdingly, fr preparatin f the lithium transitin metal xide as a raw material, cheaper chemicals can be emplyed and additinal prcedures fr remval f impurities, such as a washing step in the prir art, are nt required.
Als, in the prcess f the present inventin, n rganic slvents which may căuşe the generatin f gas during prcessing are used, whereas water which can be easily remved by apprpriate separatin such as filtering is used.
In additin, the prcess f the present inventin allws a hmgenus, thicker
aluminum-cntaining cating t be achieved, cmpared t the prir art prcess. Furthermre, the achieved cating layer has excellent mechanical stability.
In the precipitatin reactin prcess, a water-based slurry is first prepared cntaining lithium transitin metal xides particles. The slid fractin f slurry preferably exceeds 30 ~ 50% (w/w).
The aluminum salt as ne f the reactants fr the precipitatin reactin includes, fr example, but is nt limited t aluminum sulfate, aluminum ptassium sulfate, aluminum sdium sulfate, etc. Amng them, aluminum sulfate is particularly preferred because f its high cntent f Al, high slubility and large scale availability. In sme cases, the aluminum salt can be used in cmbinatin with ther salts, fr example, transitin metal sulfate such as cbalt, manganese r nickel sulfate, etc.
The base salt as the ther reactant fr precipitatin reactin includes, fr example, but is nt limited t lithium hydrxide, sdium hydrxide, ptassium hydrxide, ammnium hydrxide, sdium carbnate and the like, r mixtures f tw r mre theref. Amng them, lithium hydrxide is particularly preferred because the precipitatin reactin is pssible even at high pH withut disslutin f aluminum.
The reactin rati f aluminum salt and base salt is preferably chsen s that the pH is in the range f 6 ~12. Accrding t experiments carried ut by the inventrs f the present inventin, it was ascertained that when the equivalent f base salt is the same as r mre than the equivalent f aluminum salt, n aluminum remains in the liquid part f the slurry after the precipitatin reactin.
The reactin rati f these salts and lithium transitin metal xide partide can be determined depending upn the intended thickness f precipitate layer. In ther
wrds, where a thin layer is intended, a lw reactin rati is required. n the ther hand, where a thick layer is intended, a higher reactin rati is required.
As mentined abve, where an aluminum-dped lithium transitin metal xide is required as a cathde active material fr lithium rechargeable battery, it might be preferred t prepare an aluminum-free lithium transitin metal xide partide, either in pwder r slurry frm, and then fully cver the partide by an aluminum-cntaining precipitate layer accrding t the present inventin. The precipitate layer can be cnverted int an aluminum-cntaining, dped layer by heat treatment.
As the lithium transitin metal xide, as mentined abve, used can be LiCa, cbalt-rich Li(Mni/2Nii/2)i-xCx02, lithium manganese spinel, lithium manganese-nickel spinel, lithium manganese nickel xide, r lithium nickel xide-based materials, etc. In an embdiment, instead f lithium transitin metal xides, raw materials theref such as mixed hydrxides, r slurries cntaining the mixed hydrxides may be used. These mixed hydrxides are, fr example, M(H)2, carbnates such as MCa, r xhydrxides such as MH, wherein M basically cnsists f Mn, Ni, C, etc.
Fr example, LiNia-based materials such as LiNi.8C.i5Mn.s2, and Ni-Mn xide materials such as Li(Mni/2Nii/2)i-xCx02 are typically prepared frm precipitated hydrxides. In these cases, these hydrxides are p-Ni(H)2 type in which Ni is divalent and they d nt cntain a signifîcant amunt f anins such as S/f2 r crystalline water. Meanwhile, trivalent Al des nt fit t the crystal structure f an intended material. If Al and Ni are c-precipitated, the resulting hydrxides cntain cunter anins such as sulfate and crystalline water. Accrdingly, it is bvius that these hydrxides are less desirable fr a large scale prcess.
The lithium transitin metal xide in the preparatin prcess f the present inventin is preferably a pwder f mnlithic particles. Mnlithic is defined as partide having a small inner prsity and the typical example theref is a ptat-shaped r carse partide. After the predpitatin reactin, a cmplete, hmgenus layer f precipitate cvers the mnlithic partide. If particles are prus, less precipitate cvers the interir f the partide. Alternatively, the lithium transitin metal can be a pwder cnsisting f secndary particles, being dense agglmerates f smaller primary crystallites; hwever, it is recmmended that the inner prsity is nt t large.
The precipitatin reactin is cnducted in a precipitatin vessel as a reactr cntaining the lithium transitin metal xide slurry. Fr example, at least ne flw cntaining an aluminum salt slutin and at least ne flw cntaining a base slutin are fed t the reactr. Preferably, bth flws are injected cntinuusly and the pH is adjusted t the range f 6 ~ 12. In a preferable embdiment, the aluminuni salt is aluminum sulfate and the base is lithium hydrxide. It shuld be nted that where LiH is used as a base, predpitatin is pssible even at high pH. It is assumed that the existence f a thermdynamically stabilized phase - lithium aluminum sulfate hydrxide hydrate - reduces the tendency f aluminum t disslve at high pH.
During the precipitatin reactin, a layer f aluminum hydrxide-based material precipitates nt the surface f lithium transitin metal xide partide. As a result, an aluminum hydrxide-based layer f hmgeneus thickness, cmpletely evering the surface f lithium transitin metal xide partide, is achieved. The aluminum hydrxide-based layer is nt f simple Al(H)a but lithium-aluminum-sulfate-hydrxide-hydrate.
As mentined abve, an in exchange reactin may be further perfrmed
using a carbnate slutin after the precipitatin reactin. Fr example, a clear Li2S4 slutin, as a slutin prduced after the precipitatin reactin, is remved and then replaced by a carbnate slutin.
The carbnate fr in exchange reactin includes, fr example, but is nt limited t lithium carbnate, sdium carbnate, ammnium carbnate, ptassium carbnate r the mixture f tw r mre theref. Amng them, the lithium carbnate is mst preferable. The lithium carbnate can be used in an aqueus frm f lw cncentratin, fr example 0.1 M LiaCa. When the lithium carbnate is used, a hmgeneus layer f lithium-alurninum-carbnate-hydrxide-hydrate is btained. Hwever, it was cnfirmed that using hydrxides r ther salts instead f the carbnate were much less effective t prvide the sulfate-free precipitate layer in the present inventin, which can be seen in Example 5 f the present disclsure.
After the precipitatin reactin r the further in exchange reactin, the cated partide, mre specifically, partide cated with aluminum hydrxide-based layer, is separated and/r washed, fllwed by drying.
In an embdiment, befre r after drying, any chemical can be further added. The chemical includes, fr example, but is nt limited t LiPs, which is added preferably in an aqueus frm. In this case, the prsity f aluminum hydrxide-based layer can act like a spnge, thus supprting a hmgeneus distributin f the added liquid within the partide.
In anther embdiment, after drying, the resulthig pwder may be further mixed with any ther chemicals. The chemical includes, fr example, but is nt limited t LÎ2C03, LisAlFe, etc., which is mixed preferably in a slid pwder frm.
An aluminum-cntaining lithium transitin metal xide accrding t the present inventin can be made by perfrming a heat treatment f the cmpsite precursr as prepared abve at a temperature sufficient t sinter the lithium transitin metal xide. The temperature f heat treatment is typically in the range f 500 ~ 1050°C. At such sufficiently high temperature, the Al enrichment f the surface vanishes due t fast bulk dififusin and Al-dped lithium transitin metal xide is achieved. Hwever, if the heat treatment temperature is t lw, the surface remains Al rich and the bulk is less dped r undped. A desirable heat treatment temperature t achieve a dense surface withut excessive bulk diffusin f aluminum is 700 ~ 950°C.
PETAILED DESCRIPTIN F THE PKEFERRED EMBDIMENTS
Hereinafter, the present inventin will be described in mre detail by Examples, but the scpe f the present inventin is nt limited theret.
EXAMPLES
[Example 1]
In the present example, the precipitate f aluminum salt and base salt was investigated. A flw f l .33M A12(S04)3 slutin and a flw f 4M LiH slutin were cntinuusly fed at a cnstant rate t a reactr cntaining 200 ml f Hj during agitatin. The temperature was 60°C and pH was 9.0 when measured at 40°C. The ttal amunt f aluminum was 0.05 ml. The precipitate was washed by decanting, filtered and dried at 60°C in dynamic vacuum. The chemical analysis n the decanted and filtered slutin surprisingly shwed that n aluminum remained in the slutin.
The precipitate was investigated by ICP fr the cntents f Al and Li and by
X-ray t investigate the crystal structure. The cntent f sulfur was estimated by EDS. The result shwed that the precipitate is basically f aluminum hydrxide, additinally cntaining lithium and sulfur. The cmpsitin f Al, Li and S is apprximately Al.7Li.3(S4).2. The X-ray diffractin pattern is disclsed in FIG. 1. The X-ray pattern shws a single-phase material. Particularly, the crystal structure is different frm Al(H)s. Sulfur and lithium are part f the crystal structure and they d nt exist as a secnd phase (03804), which explains why further washing was nt effective t remve lithium and sulfur. As a result, it is cnfirmed that, after the precipitatin reactin, a litWum-aluminum-sulfate-hydrxide-hydrate hâd been frmed.
Then, an in exchange reactin was perfrmed by aging a slurry cntaining fresh precipitated lithium-aluminum-sulfate-hydrxide-hydrate in a 0.1M LiaCa slutin in which the mlar rati f €03:804 was adjusted t apprximately 5:1. The X-ray pattern btained after the in exchange reactin resembles that f lithium-alumhium-carbnate-hydrxide-hydrate(Li2Al4(C3)(H)i2*3H2).
[Example 2]
A cmmercial lithium manganese spinel (Mitsui) was used as seed particles. A slurry was prepared by adding 300 ml f Hj t 250 g f lithium manganese spinel. A flw f 1.33M 2(804)3 slutin and a flw f 4M LiH slutin were cntinuusly fed at a cnstant rate t a reactr cntaining the slurry. The temperature was 80°C and pH was 9.9 when measured at 50°C. 2.5 atm % Al was precipitated per l Mn in spinel.
The surface structure f the spinel btained after washing and drying was investigated in the same manner as hi Example l t cnfirm that the surface f the spinel is cvered by an aluminum hydrxide-based precipitate. EDS investigatin
shwed that the precipitate cntained apprximately 25% by atms f sulfur relative t precipitated Al.
[Example 3]
LiCa having the mnlithic partide mrphlgy was used as seed particles, and a slurry cntaining 2 kg f LiCCh in l L f water was prepared. Abut 200 ml f the slurry was fed t a reactr. A flw f 1.33M AlaCSa slutin and a flw f 4M LiH slutin were cntinuusly fed t the reactr at a cnstant rate. 2% by atms f Al were precipitated relative t C.
In additin, severa! preparatins were carried ut under varius reactin cnditins, i.e,, temperatures varying frm 20 t 90°C, pH varying frm abut 8 t 11, varying flw rates, etc., s that the precipitatin reactin was finished after 4,10 r 20 minutes. In sme preparatins, l ml f LiiSC per Uter water was initially added t the slurry.
The experiments shwed that in all cases, a hmgeneus layer f Al-hydrxide-based precipitate, mre specifically lithium-aluminum-sulfate-hydrxide-hydrate, fully cvering the LiC2 surface was frmed. The FESEM micrgraphs shwing such cated particles are disclsed in FIGS. 2 ~ 4. The experiments als shwed that the mrphlgy f the precipitate layer can be easily cntrlled, particularly, in view f a higher r lwer density, and different crystallite size, etc.
[Example 4]
The experiment was cnducted in the same manner as in Example 2 except that a mixed slutin f aluminum sulfate and cbalt sulfate was used instead f an
aluminum sulfate slutin. The experimental result shwed that the surface f the lithium manganese spinel was fully cvered by a cbalt-aluminum mixed hydrxide layer with hmgenius thickness, which cntained additinally sulfate and lithium.
By EDS analysis, the mlar cmpsitin rati f Al: C : S was measured t be apprximately 0.8 : l : 0.25. The lithium cntent was nt quantified.
[Example 5]
The experiment was cnducted in the same manner as in Example 3 except that a slurry was prepared frm 200 g f cmmercial LiCa and 150 ml f water, and the temperature was adjusted t 60°C, and pH was adjusted t 8.9 when measured at 40°C. The btained sample hâd a precipitate layer frmed n the surface f LiCa-The layer cntained 3% by atms f Al per l C atm.
After the precipitatin reactin, the sample was washed by decanting and divided int beakers, then lw cncentratin slutins f suitable salts, i.e., LiaCa, Na2C03 (apprximately 0.03M), LiH, NaH, LiF (apprximately 0.06M) and Li3AlF6 (.IM), respectively, were added theret. After 24h, the resulting samples were washed and dried.
The sulfur cntent and the degree f aluminum disslutin were measured by EDS analysis. The analysis result surprisingly shwed that LiaCs and NaaC3 effectively remve sulfur withut caushig Al disslutin, whereas LiH and NaH were less effective t remve sulfur and a prtin f aluminum was disslved, and furthermre LiF and LisAlFe failed t in exchange sulfur.
[Example 6]
A slurry was prepared frm 4 kg f cmmercial LiCa and 2 L f water, and sulfuric acid was added theret t neutralize the slurry. At 60°C, a fiw f 1.33M AlaCS/a slutin and a fiw f 4M LiH slutin were cntinuusly fed t the 5 L reactr cntaining the slurry with agitatin. The precipitatin reactin was cntinued fr 25 minutes with pH being adjusted t 9.6. As a result, a precipitate layer f 2% by atms f Al relative t C was frmed.
After the precipitatin reactin, the Al-cated LiCa was washed by repeated decanting. The reactr was refilled with water and 37 g f LiaCs was added and disslved with gentle stirring. After 10 hurs, the resulting LiCCh was washed by decanting, fllwed by filtering and drying.
EDS analysis shwed that LiCa cated with lithium-aluminum-carbnate-hydrxide-hydrate and substantially free f sulfur is btained. Mre specifically, apprximately 2% by atms f sulfur were present fr every Al atm present in the precipitate layer.
[Example 7]
The experiment was cnducted in the same manner as in Example 6 except that the cated LiCa after washing by decanting and flltering was nt dried. Mre specifically, instead f the filtercake being placed int a baker, a small amunt f water was added until a slurry f high viscsity was achieved. 4.5M LiPs slutin was drpped in while agitating the slurry, which was then dried. In summary, 2% by atms f P was added relative t cbalt atm.
As a result, LiCC2 cated with lithium-aluminum-carbnate-hydrxide-hydrate was additinally cated with 2% glassy LiPs.
[Example 8]
The Al-Li-H-C3 cated LiCa f Example 6 was mixed with LiaCa at an amunt f 0.4 g LiaCa per 100 g LiCC. The mixture was heated t either 750, 800, 850, 900 r 950°C.
FESEM analysis shwed that the degree f sintering and diffusin f Al int the partide can be easily cntrlled by crrect chice f sintering temperature. Specifically, at 950°C, a merely Al-dped LiC02 with a smth surface was achieved, whereas at the lwest temperature, a structured, electrically insulating layer f alurninum xide cvered the surface. At intermediate temperatures, a dense, prly structured layer based n strngly Al dped LiC2 cvered the entire surface.
As additinal experiments, 100 g samples f the Al-Li-H-Cs cated LiCi f Example 6 were mixed with 1.2 g f a ballmilled mixture f ICa and Li3AlF6 (1:2 by weight), fllwed by heating t 850, 900 r 930°C. Herein, the flurine salt acts as a sintering additive (lwering the sintering temperature required t achieve a certain degree f densifîcatin) as well as a cmpnent supplying an additinal prtective layer f LiF after the sintering.
[Example 9]
The prduct f Example 3 was heated t 700°C. Using the heat-treated prduct as a cathde active material, cîn cells were fabricated in cmbinatin with Li metal ande t perfrm the electrchemical test at 60°C. Charge and discharge rate was C/5 (C 1=150 mA/g). The cycling was perfrmed fr 32 cycles between 3.0 and 4.4V. As a cntrl grup, cin cells were als fabricated using untreated LiC02 and tested in the same manner. The result is disclsed in the graph f FIG. 5.
Referring t FIG. 5, the cells accrding t the present inventin shwed an excepţinal cycling stability cmpared t untreated LiC2. The untreated LiC02 shwed clear degradatin, visible by the suppressin f the vltage prfile at the end f discharge, and als shwed the increase f electrica! resistance, prbably due t the decmpsitin f electrlyte.
[Example 10]
Impurity-cntaining LiC.sMn.iNi.i2 was prepared by mixing a carbnate precursr, lithium carbnate and litbium sulfate, fllwed by heat treatment at 1000°C. The carbnate precursr was a mixed carbnate, btained by precipitatin f transitin metal sulfate with sdium carbnate and thus cntained a significant level f sdium impurity. Chemical analysis and EDS shwed that LiC.sMn.iNi.i2 cntained abut 5% by atms f sdium and 6% by atms f sulfur per transitin metal atm.
The impurity-cntaining LiC.sMn.iNi.ia as a precursr was cated with Al-Li-H-Cs-hydrate in the same manner as in Example 6. The experimental result shwed that during the cating prcess, sulfur and sdium impurities are remved by disslutin int slutin s that LiC.sMn.iNi.i2 cated with Al-Li-H-Cs-hydrate and practically free f sdium and sulfur impurities was achieved.
As the present inventin may be embdied in several frms withut departing frm the spirit r essential characteristics theref, it shuld als be understd that the abve-described examples are nt limited by any f the details f the freging descriptin, unless therwise specified, but rather shuld be cnstrued bradly within its spkit and scpe as defmed in the appended claims, and therefre all changes and mdificatins that făli within the meets and bunds f the claims, r
equivalences f such meets and bunds are therefre intended t be embraced by the appended claims.

We Claim:
1. A composite precursor for aluminum-containing lithium transition metal oxide
comprising (a) a lithium transition metal oxide core, and (b) an aluminum hydroxide-
based precipitate layer of active aluminum phase coated on the surface of the lithium
transition metal oxide core, with the aluminum hydroxide-based precipitate containing a
divalent anion,
wherein the total amount of aluminum in the precipitate layer is 0.5 to 5% by atoms in respect to the total amount of transition metal in the complex precursor.
2. The composite precursor as claimed in claim 1, wherein the divalent anion is sulfate and the aluminum hydroxide-based precipitate layer is of lithium-aluminum-sulfate-hydroxide-hydrate.
3. The composite precursor as claimed in claim 1, wherein the divalent anion is carbonate and the aluminum hydroxide-based precipitate layer is of lithium-aluminum-carbonate-hydroxide-hydrate.
4. The composite precursor as claimed in claim 1, wherein the lithium transition metal oxide as the core of composite precursor has a layered or spinel crystal structure.
5. A process for preparation of the composite precursor as claimed in claim 1, comprising a step of carrying out the precipitation reaction of an aluminum salt solution and base solution with a lithium transition metal oxide as seed particles dispersed in a water-based slurry or paste to form aluminum hydroxide-based precipitate layer on the surface of lithium transition metal oxide particle,
wherein the aluminum salt is one or more selected from the group consisting of aluminum sulfate, sodium aluminum sulfate and potassium aluminum sulfate, and wherein the base salt is one or more selected from the group consisting of lithium hydroxide, sodium hydroxide, ammonium hydroxide and potassium hydroxide.
6. The process as claimed in claim 5, wherein after the precipitation reaction, an ion
exchange reaction is further performed to replace the sulfate present in the precipitate
layer by carbonate by adding a carbonate solution into a reaction system.

7. The process as claimed in claim 5, wherein the lithium transition metal oxide as a raw material is tolerated to contain impurities of sulfur, sodium or chloride.
8. The process as claimed in claim 5, wherein the aluminum salt is aluminum sulfate.
9. The process as claimed in claim 5, wherein the aluminum salt is used in combination with cobalt and/or nickel sulfate.
10. The process as claimed in claim 5, wherein the base salt is lithium hydroxide.
11. The process as claimed in claim 5, wherein the precipitation reaction is conducted by feeding at least one flow containing an aluminum salt solution and at least one flow containing a base solution to in a precipitation vessel containing the lithium transition metal oxide slurry.
12. The process as claimed in claim 6, wherein the carbonate is one or more selected from the group consisting of lithium carbonate, sodium carbonate and ammonium carbonate.
13. The process as claimed in claim 12, wherein the carbonate is lithium carbonate of a low concentration.
14. The process as claimed in claim 5, wherein after the precipitation reaction or after the further ion exchange reaction of claim 6, the coated particle is separated and/or washed, followed by drying.
15. The process as claimed in claim 14, wherein before or after drying, any other chemical additive such as LiPO3 is further added in an aqueous form.
16. The process as claimed in claim 14, wherein after drying, any other chemical such as Li2CO3 or Li3AlF6 is mixed in a solid, powder form.
17. An aluminum-containing lithium transition metal oxide for a cathode active material of lithium rechargeable battery, produced by heating the composite precursor as claimed in

claim 1 in the range of 500 ~ 1050°C.
18. The aluminum-containing lithium transition metal oxide as claimed in claim 17, wherein the temperature of heat treatment is 750 ~ 950°C.