CN101616870B - Island-covered lithium cobaltite oxides - Google Patents

Island-covered lithium cobaltite oxides Download PDF

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CN101616870B
CN101616870B CN2008800034640A CN200880003464A CN101616870B CN 101616870 B CN101616870 B CN 101616870B CN 2008800034640 A CN2008800034640 A CN 2008800034640A CN 200880003464 A CN200880003464 A CN 200880003464A CN 101616870 B CN101616870 B CN 101616870B
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licoo
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island
lithium transition
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CN101616870A (en
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珍斯·马丁·鲍尔森
托马斯·劳
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Umicore NV SA
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Abstract

Disclosed is a cathode active material and a method to produce the same at low cost. The cathode powder comprises modified LiCoO2, and possibly a second phase which is LiM'O2 where M' is Mn, Ni, Co with a stoichiometric ratio Ni: Mn >=1. The modified LiCoO2 is Ni and Mn bearing and has regions of low and high manganese content, where regions with high manganese content are located in islands on the surface. The cathode material has high cycling stability, a very high rate performance and good high temperature storage properties.

Description

Island-covered lithium cobaltite oxides
The present invention relates to a kind of powder lithium transition-metal oxide, wherein comprise the LiCoO that particular type has Mn and Ni 2This cathode powder can be used technology large-scale production at a low price.More particularly, said preparation is the mixture sintering thing that contains cobalt precursors, contains cobalt precursors such as LiCoO 2, contain the Ni-Mn-Co precursor, like mixed hydroxides MOOH and Li 2CO 3The enough high LiCoO of sintering temperature to allow to form 2And cationic exchange between the Li-Ni-Mn-Co oxide phase, this generation has the very specific form of different transiting metal component gradients.Said lithium transition-metal oxide powder can be as the cathode active material in the chargeable lithium cell.
Some inherent limitations such as fail safe are relatively poor, cost is high, LiCoO although have 2Remain the chargeable lithium cell cathode material of maximum application.The consumer need increase the energy density of chargeable lithium cell strongly.A kind of method of improving energy density is to increase charging voltage, and this needs can be at the firm cathode material of high-voltage charge more.Charging voltage occurs or more serious problem is if increase
(a) fail safe is low,
(b) during the high temperature storage rechargeable battery storage performance relatively poor and
(c) cyclical stability is relatively poor.Disclosing a lot of methods is used to address these problems.Implementation part improves, but does not fully solve basic problem.
Except that requiring to increase the energy density, require rechargeable battery to satisfy energy demand.This means battery generally and particularly active cathode material itself have the performance of enough high speeds.
There is popular tendency in this.Scrutinize the open result of cathode material, with better understanding based on LiCoO 2The defective of chargeable lithium cell.
A basic defect derives from a surface area difficult problem.Can satisfy the performance (being high power) that gathers way through increasing surface area, because can reduce solid-state lithium diffusion length; This causes improving speed ability.Yet high surface has increased the zone that undesirable side reaction between electrolyte and the charged cathode wherein occurs.These side reactions are processes that fail safe under high pressure is relatively poor, cyclical stability is relatively poor, and the storage performance of charged cathode is relatively poor when high temperature.In addition, high surface area material often has low storage density, and this has reduced volume energy density.
Another basic defect derives from the cobalt stoichiometry.Lithium nickel-manganese oxidation cobalt-based cathode material is (like LiMn 1/3Ni 1/3Co 1/3O 2) have a LiCoO of ratio 2The stability of reacting between higher potential resistance to electrolyte contamination and the negative electrode, and the cost of raw material is lower, but these materials receive low volume energy density puzzlement, and these materials have lower lithium diffusion constant usually.
Can sum up and wherein have basic restriction:
-surface area: hope that the low surface area cathode material has high security at memory period, the density of improvement and high stability; Yet, the performance because this will underspeed, surface area can not too reduce.
-composition:, hope LiMO if M mainly is a cobalt 2Negative electrode obtains high lithium diffusion rate and high volume energy density; Yet the high-load cobalt causes fail safe relatively poor, and it is relatively poor to increase cost and high-voltage stability.
A kind of method that solves this difficult problem is to increase diffusion constant.Increase D and will reduce surface area, do not lose speed ability.
LiMO was before disclosed 2, M=Ni-Mn-Co wherein, Ni: Mn＞1.US6 for example, 040,090 (Sanyo) discloses the multiple LiMO of comprising 2, and the LiMO of Ni: Mn＞1 2(M=Mn, Ni Co) form.This patent application discloses the have high-crystallinity LiMO of (small peak HWFM in the X-ray diffractogram) 2Patent US7 discloses the LiCoO that for example is doped with Ni and Mn in 078,128 2US7,078,128 discloses the LiCoO that preferred use is doped with equivalent Ni and Mn 2
European patent application EP 1716609 A1 disclose a kind of LiMO 2The base active cathode material, wherein the particle composition depends on particle size, particularly along with the reduction of particle size, particulate cobalt content reduces.Because the core-shell structure particles cobalt content reduces, and wherein contains the Mn-Ni shell and has identical thickness, is covered with LiCoO 2Nuclear.As a result, little like fruit granule, LiCoO 2Examine for a short time, the cobalt content of whole particle is lower.
European patent application EP 1556915 A1 disclose a kind of LiMO with transiting metal component gradient 2This gradient is obtained from the mixed hydroxides shell, is covered with to have the nuclear that obvious different metal is formed.The optimal way center is LiCoO 2Behind the sintering, the transition metal composition gradient that acquisition has the stoichiometry radial variations, and LiMO 2Shell covers LiCoO 2Base nuclear.During the sintering, cobalt is from LiCoO 2Nuclear proliferation is to LiMO 2Shell.Simultaneously, still less Ni from LiMO 2Shell diffuses into LiCoO 2Nuclear.Therefore, shell swelling and LiCoO 2Nuclear shrinks.The swelling shell that covers retract produces the space usually between shell and nuclear.These spaces are very undesirable.
The objective of the invention is to define a kind of cathode material, and reveal the high stability that prolongs cycle period at the high charge voltmeter with high speed performance.Improved the high-temperature storage performance in addition.With comprising the LiCoO that contains Mn and Ni 2The powder lithium transition-metal oxide of particle is realized this point, and said particle has Mn and Ni enrichment island in its surface, and said island comprises 5mol% at least, the preferred Mn of 10mol% at least.
Mn and Ni enrichment island preferably have the thickness of 100nm at least, and cover less than 70%, preferably less than 50% the said LiCoO that contains Mn and Ni 2Particle surface.In addition, in the said island Mn concentration preferably than the said LiCoO that contains Mn and Ni 2The high at least 4mol% of Mn concentration in the particle body, preferably high at least 7mol%.
In another embodiment, the said LiCoO that contains Mn and Ni of Ni concentration ratio in said Mn and the Ni enrichment island 2The high at least 2mol% of Ni concentration in the particle body, preferably high at least 6mol%.The LiCoO that preferably contains Mn and Ni 2Particle comprises 3mol% at least, more preferably 10mol%Ni and Mn at least.In a preferred embodiment, the said LiCoO that contains Mn and Ni 2The lattice constant a of particle and c are respectively 2.815+/0.002 and 14.05+/-0.01.
The LiCoO that preferably contains Mn and Ni in addition 2Particle is a monoblock, and inside does not have hole.In addition, the said LiCoO that preferably contains Mn and Ni 2The distribution of sizes of particle has the d50 greater than 10 μ m, is preferably greater than 15, most preferably greater than 20 μ m.
In another preferred embodiment, the powder lithium transition-metal oxide comprises the LiCoO of said Mn of containing of 30wt% to 95wt% and Ni 2Particle.
The present invention also comprises a kind of lithium transition-metal oxide, and it has the LiCoO by said Mn of containing and Ni 2First phase that particle constitutes comprises second no island phase: the Li with following general formula in addition 1+aM ' 1-aO 2 ± b, wherein-0.03＜a＜0.05, and b＜0.02, M '=Ni mMn nCo 1-m-n, m>=n wherein, 0.1＜m+n＜0.9.Then this powder lithium transition-metal oxide preferably has Li xM yO 2 ± δTotal composition, 0.97＜x＜1.03,0.97＜y＜1.03 wherein, x+y=2, δ＜0.05, and M=Co 1-f-gNi fMn g, 0.05＜f+g＜0.5 wherein, f>=g.Preferred in addition 0.98＜x/y＜1.00.In another preferred embodiment, said oxide only constitutes by two mutually, and first is the LiCoO of said Mn of containing and Ni mutually 2Particle, second is said no island phase mutually.
The lattice constant a ' of preferred in addition said no island phase and c ' with reference to lithium transition-metal (M Ref) the lattice constant a " and c " of corresponding no island phase of oxide has following relationship, wherein has identical composition Li xM yO 2 ± δ, and by pure LiCoO 2Particle constitutes with said corresponding no island mutually:
0.980＜a '/a "＜0.998 and 0.9860＜c '/c "＜0.9985,
Preferred 0.990＜a '/a "＜0.997,0.9920＜c '/c "＜0.9980.
If for example from Co precursor and composition M "=Ni mMn nCo 1-m-nMixed metal hydroxides prepare material LiMO of the present invention 2, then lattice constant a " and c " is meant and has composition LiM " O 2Reference material, different lattice constant a ' and c ' are illustrated in LiCoO 2Base first mutually and do not have island second and enough cation exchange occur between mutually.
No island preferably has secondary granule mutually, and it has the particle size distribution of 2 to 10 microns d50, and said secondary granule is made up of the elementary crystal grain agglomerate of 0.5 to 2 μ m d50 particle size distribution of sintering.In another preferred embodiment, said Mn further comprises Ti with Ni enrichment island with said no island mutually, and wherein Ti content is less than oxide Li xM yθ 2 ± δThe M of middle 10mol%.
More preferably, at oxide Li xM yO 2 ± δIn, the powder lithium transition-metal oxide further comprises less than one or more of 5mol%M and is selected from the alloy of Al and Mg, and is selected from the alloy of Be, B, Ca, Zr, S, F and P less than one or more of 1mol%M.
For simplicity, in this specification, contain the LiCoO of Mn and Ni 2Particle is commonly referred to ' mutually 1 ' or be also referred to as ' modification LiCoO 2Phase ', have general formula Li 1+aM ' 1-aO 2 ± bNo island be called mutually lithium transition-metal oxide ' LiM ' O 2' (M '=Ni-Mn-Co) mutually or ' mutually 2 ', be also referred to as ' cathode material '.
Surprisingly, if the invention discloses to cause during the sintering at LiCoO 2And LiM ' O 2Between these mixtures of the mutual heat treatment of method (co-sintering) of exchange cation, can significantly improve LiCoO 2(mutually 1) and have Ni: the LiM ' O of Mn ratio＞1 2(M '=Ni-Mn-Co) speed ability of the mixture of (phase 2), generation phase 1 and the composition distribution of 2 particles mutually.Obtain 1 particle (LiCoO mutually simultaneously 2) specific modality.With containing manganese LiM ' O 2Sheet material partly covers said particle.The author claims that this form is " island " form.Simultaneously, surprisingly, equally significantly improved high-voltage stability.
The form of modification LiCoO has the intensive modification LiCoO that sinters to 2The island of body produces the partial gradient of transition metal chemistry metering.Said island comprises high concentration manganese.LiCoO 2And LiM ' O 2Particle has the distribution of composition.In addition, LiM ' O 2Particle has the form that depends on cobalt content.The size of elementary crystal grain increases along with cobalt content.Opposite with above-mentioned EP1556915 A1, there is not stoichiometric radial variations among the present invention.It is equivalent to have LiMO 2The multicenter gradient on island, this LiMO 2The island is positioned at the surface and as the gradient center.In addition, the LiCoO that is only partly covered by the island 2It is very important difference.
Another importance of the present invention is that said island does not cover LiCoO fully 2Particle.Can be through mixed hydroxides be deposited to LiCoO 2Realize on the surface covering fully-in other words-LiCoO 2Nuclear-LiM ' O 2Shell morphology.This method has been disclosed among above-mentioned patent application EP1556915A1 and the EP1716609 A1 (people such as Paulsen).MOOH shell-LiCoO 2The situation of nuclear precursor has two major defects, and is of following document: as to have the nucleocapsid cathode material of the composition that depends on size, Jens M.Paulsen; Jong-Seok Jeong; And Ki-Young Lee, Electrochem.Solid-State Lett., volume 10; The 4th phase, A101-A105 page or leaf (2007).(1) this technology is more expensive, and more cobalts get into shell from nuclear proliferation during (2) sintering.Therefore shell expands, and nuclear shrinks simultaneously.This causes shell to separate from the nuclear part usually, produces big cavity.These big cavitys are very undesirable because: (i) their increase pores-so the decrease of power density and (ii) the overslaugh lithium pass cavity and directly diffuse into or leave LiCoO 2The nuclear zone of particle-so cause losing speed ability.
This situation is different from cathode material of the present invention.Contain the manganese island and only covered LiCoO 2The sub-fraction of particle surface.Therefore cobalt spreads island swelling and the LiCoO that causes 2Nuclear shrinks and does not produce big cavity.The result can obtain high volume density and high speed performance.
The present invention also comprises a kind of electrochemical cell that comprises negative electrode, and described powder lithium transition-metal oxide was as active material before said negative electrode comprised.
A kind of be used to prepare before the method for described powder lithium transition-metal oxide, comprise step:
-LiCoO is provided 2Powder or cobalt content at least 90mol% the mixture that contains cobalt precursors compound and Li-Ni-Mn-Co oxide or Ni-Mn-Co precursor powder and optional Li precursor compound (preferred lithium carbonate) and
-at least 900 ℃, preferred at least 950 ℃ the said mixtures of temperature T sintering, sintering time t is 1 to 48 hour, to obtain to have in its surface the LiCoO that contains Mn and Ni on Mn and Ni enrichment island 2Particle.
Thereby, through at high temperature surpassing 900 ℃ of sintering LiCoO 2Based powders and Li-Ni-Mn-Co-oxide or contain the Ni-Mn-Co powder and lithium source such as Li 2CO 3Mixture and prepare cathode material.This temperature must surpass 900 ℃, for example 910 ℃ or 920 ℃.During the sintering, LiCoO 2The partial cation exchange appears in particle and containing between the Ni-Mn particle.If sintering temperature is low, then do not have enough cation exchange, and negative electrode does not show high speed performance.If sintering temperature is high, then particle becomes too fine and close, and metal ingredient is too average, i.e. LiCoO 2And the too much cation exchange of appearance between the Mn-Ni-Co.In the case, will there be Mn and Ni enrichment island on the first phase particle.
Alternatively, can mix and contain cobalt precursors powder (like cobalt oxide, cobalt hydroxide or cobalt carbonate) and contain Ni-Mn-Co powder and lithium source, subsequently through at high temperature, preferably above 950 ℃ of following sintering.
A kind of method that is used to prepare the powder lithium transition-metal oxide that has two phases as stated comprises step:
-LiCoO is provided 2Powder or cobalt content at least 90mol% the mixture that contains cobalt precursors compound and Li-Ni-Mn-Co-oxide or Ni-Mn-Co precursor powder and optional Li precursor compound (preferred lithium carbonate) and
-at least 900 ℃, preferred at least 950 ℃ the said mixtures of temperature T sintering, sintering time t is 1 to 48 hour,
To obtain the LiCoO of said Mn of containing and Ni 2Particle mutually with said no island with lattice constant a ' and c ' mutually, it has following relationship, the reference lithium transition-metal (M that wherein obtains at the said Ni-Mn-Co precursor powder of uniform temp T sintering and said Li precursor compound uniform temp T and identical time t Ref) the said relation of lattice constant a " and c " of oxide or said Li-Ni-Mn-Co-oxide is
0.980＜a '/a "＜0.998 and 0.9860＜c '/c "＜0.9985,
Preferred 0.990＜a '/a "＜0.997 and 0.9920＜c '/c "＜0.9980.
In these methods, the Ni-Mn-Co precursor powder is transition metal hydroxide, hydrogen oxide oxide, carbonate, oxycarbonate, or lithium transition metal compound, wherein transiting metal component M " being M "=Ni oMn pCo 1-o-p, wherein o+p＞0.5, and o＞p.In addition, the Ni-Mn-Co precursor powder preferably includes the levels of transition metals of 5 to 70mol% said powder lithium transition-metal oxides.
In the embodiment, the LiCoO of use 2Powder has the tap density of at least 2 gram/cubic centimetres, and is made up of the monoblock particle of d50 at least 10 μ m, preferably these d50 at least 15 μ m, most preferably at least 20 μ m.
On the other hand, contain hydroxide, oxyhydroxide or the carbonate that the cobalt precursors compound is preferably a kind of or more kinds of cobalts.
In another embodiment, said LiCoO 2Or contain the transition metal that cobalt precursors comprises at least 80% said powder lithium transition-metal oxide, containing the Ni-Mn-Co precursor powder is that the particle of 1 to 3 μ m particle size distribution is formed by d50.
In another embodiment, said LiCoO 2Or contain cobalt precursors and comprise the transition metal that is lower than 80% said powder lithium transition-metal oxide, contain the Ni-Mn-Co precursor and form by the Conglobation type particle of d50 particle size distribution with 4 to 10 μ m.
In these two embodiments, contain the Ni-Mn-Co precursor and can further comprise Ti, be preferably the TiO that d50 is lower than 100 nanometers 2Particle form.
Below details of the present invention further is discussed.
Cathode material of the present invention is a powder, wherein comprises modification LiCoO 2Still be not only second transition metal mutually with major part.Two are the lithium transition-metal oxide phase with layering crystal structure mutually: orderly rock salt crystal structure-space group r-3m.Negative electrode can be stoichiometry Li 1M 1O 2, wherein M is cobalt, manganese and/or nickel, or slightly poor lithium (Li 1-xM 1+xO 2) or rich lithium Li 1+xM 1-xO 2, x＜0.3 wherein.Usually suspect and have non-stoichiometric oxygen.Therefore oxygen stoichiometry is approximately 2.0, but can not get rid of negative electrode for omiting oxygen deprivation or oxygen coalescence.Therefore all consist of Li xM yO 2 ± δ, 0.97＜x＜1.03,0.97＜y＜1.03 wherein, x+y=2, δ＜0.05.M is manganese, cobalt and nickel, M=Co 1-f-gNi fMn g, condition is 0.05＜f+g＜0.5, and f>=g.
First is obtained from LiCoO mutually 2Precursor, and be modification LiCoO 2This composition can be defined as LiCo 1-a-bNi aMn bO 2, a>=b wherein, 0.03＜a+b＜0.5, preferred 0.1＜a+b＜0.5.This general formula is Utopian, does not consider little possibility deviation such as lithium is excessive or lack oxygen non-stoichiometry or aforesaid doping.Preferred LiCoO 2The base particle is a monoblock.The particle of monoblock does not show internal void, and is not made up of littler primary granule aggregate.One aspect of the invention is for forming incomplete same LiCoO 2The variable grain of phase.The actual composition of particle depends on that how much nickel and manganese diffuse into LiCoO during the sintering 2Particle.Ni and Mn are obtained from second mutually the precursor, it typically is mixed hydroxides.Except many other factorses such as temperature Li: M ratio etc. diffuse into LiCoO during the sintering 2The Mn of base phase and Ni amount depend on arrangement, contact area and the contact pressure of adjacent Ni-Mn base particle to a great extent.As a result, different LiCoO 2Particle has different compositions.
Secondly, the very important aspect of the present invention is single LiCoO 2It is not uniform that the metal of base particle is formed.Typical case's particle has the island configuration of surface, and this island is obtained from the intensive LiCoO of sintering to 2The less Ni-Mn base particle or the crystal grain of particle surface.This island has the manganese concentration that is higher than away from zone, island or granule interior zone.Having the island form is the inherent feature of cathode material of the present invention.Higher manganese content center, these islands-have-can't with particle separation.They are intensive and be connected to LiCoO continuously 2The particle main body.Therefore manganese metering-along with the island apart from increasing-possibly reduce, in granule interior or be far apart between the island on the surface near zero with the gradual change similar fashion.The inventor notices that the island form relates to the observed speed ability of open cathode material.If the author thinks island-be free of attachment to LiCoO 2Particle-will have different lattice constants.Yet, the intensive LiCoO that is connected in island 2, at LiCoO 2The zone that has manganese metering gradual change between particle and the island.Therefore island and particle will suffer strong lattice strain.Strain reason-author does not know accurate mechanism-make lithium can obviously diffuse into particle quickly.
Second is LiM ' O mutually 2, M '=Ni wherein mMn nCo 1-m-n, m>=n, this general formula of 0.1＜m+n＜0.9 is Utopian, does not consider little possibility deviation such as lithium is excessive or lack, oxygen non-stoichiometry or mix as stated.Second preferably is obtained from mutually and contains Ni-Mn-Co precursor such as mixed hydroxides, mixed oxidization hydroxide, mixed oxide, hybrid metal lithium oxide or mixed carbonate.The metal of second phase is formed change during the sintering.Cobalt is from LiCoO 2Particle diffuses into LiM ' O 2Particle.LiM ' O is left in some Ni and Mn diffusion 2Particle gets into LiCoO 2Particle.As a result, the cobalt stoichiometry of second phase is higher than the cobalt stoichiometry that contains the Ni-Mn-Co precursor.Changing the cobalt stoichiometry is importance of the present invention.Only during sintering, significantly increase the cobalt stoichiometry, produce enough cation exchange, and only fully improve the speed ability of the negative electrode that obtains in this case.
The inventor has two more surprising observations, and this is considered to another basic sides of the present invention:
First observation: the second part increase mutually during the sintering.Obviously, compare and diffuse into LiCoO 2The nickel of phase and manganese, more cobalt diffuses into the second phase (LiMO 2).The inventor thinks that the difference in this diffusion has strengthened observed island form.Relevant with this observation is the clear variation of voltage curve.LiCoO 2And LiM ' O 2Mixture have character voltage curve at the 3.88V platform.Along with cation exchange increases, the author observes the 3.88V abolition of plateau, and the discharge voltage tail end reduces.In addition, cobalt not only diffuses into LiM ' O 2Particle, and diffuse into the zone that contains manganese on the surface; During this technology, the effect of Co source is played in the zone between the island.Island itself is the cobalt absorbent simultaneously.In the sketch-contain the manganese island with the cobalt swelling, just as sponge water absorption and swelling around it.How this description of the process produces the island form.
Second observes: first has mutually and obviously is different from pure LiCoO 2Composition.The major part of the first phase particle comprises at least 3%, more preferably 10% manganese and nickel.This stoichiometry changes the significant change that is accompanied by lattice constant usually.Yet X-ray diffraction analysis shows that surprisingly the lattice constant (deriving from two phase Rietveld purifies) of first phase is basically less than variation-they keep and LiCoO 2Identical.The inventor believes that this is the very important aspect of the present invention, and the improvement that shows the first phase velocity performance is not because at LiCoO 2And LiM ' O 2Between form solid solution and produce.(solid solution shows that the gradual change of lattice constant depends on its composition.)
Another aspect of the present invention is LiM ' O 2Particle (second phase) has crystal grain, and the size of said crystal grain is relevant with cobalt content.Obviously, during the sintering, along with LiM ' O is left in more Ni (and Mn) diffusion 2, get into LiCoO 2Particle, and along with more Co diffuse into LiM ' O 2Particle causes crystal grain accelerated growth.As a result, has the stoichiometric LiM ' O of higher cobalt 2Particle (second phase) has bigger elementary crystal grain.This is very useful technology, because obtain to optimize form with the self-organizing mode.This is because the cobalt content increase causes lithium to spread sooner, and this allows big crystal grain and does not lose speed ability.Yet the relation between high cobalt content and the large-size only is meant the size of crystal grain, is not meant particle diameter.Larger particles on average has and is lower than short grained cobalt stoichiometry probably, the longer path of diffusion because more cobalts are had to.
The inventor understands this reaction and produces the island form that is described below: during the sintering, and less and reunion LiM ' O 2The major part contact LiCoO of particle 2Particle.This contact point is the cobalt pond, and at LiCoO 2Form inner the embedding on the particle surface and contain the manganese island.Simultaneously, nickel (with some manganese) diffuses into LiCoO 2, and cobalt diffuses into LiM ' O 2Particle.During the sintering, since cobalt picked-up and thermal sintering, reunion LiM ' O 2The density of particle increases.During the densification, swelling island and LiM ' O 2Contact loss between the particle, and obtain by two final negative electrodes of becoming of homophase groups of grains not.
If LiM ' is O 2Particle is an aggregate, LiM ' O 2And LiCoO 2Between contact lose easily.In this case, only consume partial L iM ' O 2Particle, and form the island seed.Alternatively, if the Ni-Mn-Co precursor has the very little particle that d50 is lower than the 1-2 micron, require not have contact loss.In this case, consume most of and even whole Ni-Mn-Co particle, form the island seed.Therefore, different execution mode of the present invention is feasible.
First exemplary embodiment: preferred especially Ni-Mn-Co precursor is made up of reunion crystal grain.A preferred embodiment is a mixed hydroxides, and wherein secondary granule is made up of not too fine and close primary granule aggregate.Very fine and close and bigger Ni-Mn-Co precursor is not too suitable.Preferable particle size distributes and has the d50 of 4-8 micron.LiM ' O in this case 2Particle is enough little, and consequently (a) supports very high speed and (b) their embed big LiCoO just 2The space of particle, this allows low porosity electrode and high volume energy density.
Preferably, the first phase (LiCoO 2) precursor be that monoblock is fine and close, and have much larger than second phase (LiM ' O 2) size of precursor, and this second phase (LiM ' O 2) be reunion, not too fine and close, and have reduced size.The preferred precursor of first phase is to have the LiCoO of the fine and close monoblock particle of 10-20 micron at least 2Many commercial LiCoO 2Material has this required form.Alternatively, if having larger particles (10-20 micron at least) and high density, cobalt hydroxide, cobalt oxidation hydroxide, cobalt oxide or cobalt carbonate are suitable precursor.For example suitable precursor is cobalt hydroxide or hydrogen oxide oxide, and it is rough spheric granules, and vibration density is higher than 2.0 gram/cubic centimetres, and the d50 of particle size distribution is greater than the 15-20 micron.
If the Ni-Mn-Co precursor is an aggregate, and have the particle size distribution that d50 is the 4-10 micron, at least 20% transition metal of then preferred final negative electrode is obtained from the Ni-Mn-Co precursor, and is lower than 80% transition metal and is obtained from LiCoO 2Precursor.
Second exemplary embodiment: also preferred Ni-Mn-Co precursor is made up of very little particle.An instance has the typical particle that is lower than the 0.5-1.5 micron for spraying the mixed hydroxides of milling.In this case, preferably be lower than 20 or even 15% final negative electrode transition metal be obtained from the Ni-Mn-Co precursor, yet at least 80, preferred 85% is obtained from cobalt precursors.Preferred cobalt precursors is made up of larger particles (d50＞10-20 micron), and this particle is densification and monoblock.Suitable cobalt precursors is commodity LiCoO 2, or high density (vibration density＞2 gram/cubic centimetres) cobalt hydroxide, hydrogen oxide oxide or carbonate.For example, suitable precursor is shaped as spherical or irregular potato shape particle.
Two kinds of exemplary embodiment are not regarded as replacement scheme, but are equivalent to two extreme, example.For example; The feasible Ni-Mn-Co precursor that comprises little (being lower than the 0.5-1.5 micron) particle and big (4-8 micron) agglomerated particle, has bimodal grain size distribution that is to use; Wherein most of granule is consumed and forms the island, and the wherein major part of larger particles separation during the sintering.Feasible in addition less cobalt granule and the sub-micron MOOH of being to use can expect the hypervelocity performance in this case.
Contain the formation reaction on manganese island in two execution modes, be attended by the cation exchange between cobalt and the nickel.The inventor thinks that the basic sides that forms the island form is that the mobility of (4 valency) manganese is lower than LiCoO 2In 3 valency nickel and LiM ' O 2In 3 valency cobalts.In addition, during the cell charging, (4 valency) manganese is not participated in electrochemistry insertion/extraction lithium, and some manganese can be replaced by other cation.Suitable in addition cation is a titanium.Be similar to manganese, it is the electrochemistry inertia, have than Hypomobility, and the entering Ni-Mn-Co precursor that can mix.For example, be similar to manganese, titanium can mix and get into LiNiO 2
Even another importance of the present invention is a cathode material is lithium substoichiometric a little, also can obtain high speed performance.We notice if total lithium content of every transition metal is approximately 0.98 and promptly are lower than one, obtain the maximum speed performance.This is very surprising, because M comprises the lithium transition-metal oxide Li of nickel therein 1+zM 1-ZO 2Situation under, what accept extensively is that lithium lacks and to cause cation (being that the nickle atom misplace is on crystallization lithium site), and the cation that increases causes speed ability relatively poor.
Explain that Summary of drawings of the present invention is following:
Fig. 1: the SEM micrograph of sample REF1 and REF2.
Fig. 2: the scanning electron microscopy of sample CX2 and CX3.
Fig. 3: the scanning electron microscopy of sample EX1 and EX3.
Fig. 4: sample EX2-is 1 and 2 scanning electron microscopy mutually.
Fig. 5: be used for the EX1 particulate scan electron micrograph that EDS analyzes.
The EDS drawing of phase 1 particle of Fig. 6: EX1.
Fig. 7: be used for the EX1 particulate scan electron micrograph that EDS analyzes.
Fig. 8: the scanning electron microscopy that is used for EX1 phase 2 particles of EDS analysis.
Fig. 9: commodity LiCoO 2(REF1) and the cycle performance of sample EX4
Figure 10: the scanning electron microscopy of sample EX5E and CX6.
Figure 11: the crystallization figure of REF 1-2, CX2-3 and EX 1-3.
Figure 12: the crystallization figure of REF 1-2, CX5 and EX4-5.
The X-ray diffractogram of Figure 13: CX2, CX4 & CX5 and EX1.
The X-ray diffractogram of Figure 14: CX6 and EX9E.
Figure 15: CX2, CX3 and the EX1-EX3 voltage curve of slow interdischarge interval.
Figure 16: the cycle performance of sample EX1 and speed ability.
Figure 17: the speed ability of comparative sample CX6 and EX5E.
The following example further specifies some aspect of the present invention.Following tabulation provides experimental condition and result's general introduction.
Table 1 general introduction sample and preparation condition
Table 2 general introduction X ray and BET surface data.
Table 3 general introduction derives from the electrochemical results of button cell
The reference implementation example
Use following reference sample:
-REF1-LiCoO 2Be commodity LiCoO 2, and have the d50 of ≈ 20 μ m, and form by monoblock, fine and close particle.
-from mixed hydroxides MOOH and Li 2CO 3, in air, prepare REF2-LiM ' O with 950 ℃ 2Li: the M ratio is Li: M '=1.01: 1, M '=Ni 0.53Mn 0.27Co 0.2REF2 has agglomerate morphology.
Before button cell assembly and BET measure, in 8 hours, with 850 ℃ of heated sample REF1 and REF2 again.The measured X x ray diffration pattern x, and carry out Rietveld and purify.Fig. 1 has showed the scanning electron microscopy of sample REF1 and REF2.Left hand view has been showed REF1 with the 1000x multiplication factor.Particle is erose.There is not the island form.Right part of flg has been showed REF2 with the 2500x multiplication factor.Particle is an aggregate, is made up of the elementary crystal grain that sinters bigger erose secondary granule into.
Calculate embodiment
For imaginary calculation sample CC1, through calculating the average weight of REF1 and REF2 analog value, estimate desired value, capacity and the speed ability of BET surface area, wherein sample CC1 is 60%REF1-LiCoO 2And 40%REF2-LiM ' O 2Mixture.
The comparative example
Embodiment C X2: through mixing 60%REF1-LiCoO 2With 40%REF2-LiM ' O 2The preparation cathode powder.Before the mixing, in air in 5 hours, with 850 ℃ of heat treatment REF1-LiCoO 2And REF2-LiM ' O 2Whole LiM ' O that consist of of final CX2 negative electrode 2, M '=Co wherein 0.68Ni 0.21Mn 0.11Fig. 2 a has showed the scanning electron microscopy (5000x multiplication factor) of biased sample CX2.Measure the BET surface area of mixed-powder CX2.Can observe and not have the island form.The preparation button cell, measuring capacity, irreversible capacity, cyclical stability and speed ability.The measured X x ray diffration pattern x, and carry out Rietveld and purify.Take scanning electron microscopy.
Table 2 and 3 has showed that sample CX2 has the character that is similar to precursor average weight among the imaginary sample CC1 substantially.This mixing does not have obvious benefit to speed ability or cyclical stability.Scanning electron microscopy confirms LiCoO 2Particle does not have the island form.Rietveld purifies and confirms from the lattice constant of mixture X ray diagram acquisition and from LiCoO 2And LiM ' O 2The lattice constant that obtains respectively of X ray picture identical.
Embodiment C X3: through mixing 60%REF1-LiCoO 2With 40%REF2-LiM ' O 2The preparation cathode powder.In air, in 5 hours,, produce sample CX3 with 850 ℃ of these mixtures of heat treatment.Whole LiM ' O that consist of of negative electrode 2, M '=Co wherein 0.68Ni 0.21Mn 0.11, identical with CX2.Fig. 2 b has showed the scanning electron microscopy of sample CX3.Multiplication factor is 2500x.There is not the island form.
Obviously, compare with CX2 (being the mixture of heat treated sample), the character of sample CX3 (being thermally treated mixture) such as cyclical stability and speed ability are improved a little.Rietveld purifies and confirms to constitute compound L iM ' O 2And LiCoO 2Lattice constant during heating treatment do not have significant change.
The constant of REF1 is identical with phase 1 among CX2 and the CX3, and the lattice constant of REF2 is identical with phase 2 among CX2 and the CX3.
Embodiment C X4: according to comparative example CX3 in the cathode powder that identical method is prepared as thermally treated mixture is described, replaced in 5 hours producing sample CX4 except being used in 900 ℃ of heating 850 ℃ of heating 5 hours.The preparation button cell.The measured X x ray diffration pattern x, and carry out Rietveld and purify.Take scanning electron microscopy.
Table 2 and 3 has showed that sample CX4 has the character that is similar to substantially at the CX3 of low temperature preparation.Scanning electron microscopy shows does not have the island form basically.X-ray diffraction shows the phase mixture of two phases, and first has REF1-LiCoO 2Lattice constant, second has the sample of being similar to REF2-LiM ' O 2Lattice constant.Obviously, Co does not appear from phase 1 LiCoO 2Obviously diffuse into the second phase LiM ' O 2Speed ability is similar to sample CX3.This comparative example shows that heat treatment temperature is increased to 900 ℃ from 850 ℃ and does not obviously improve the button cell performance.
The embodiment of the invention
Embodiment 1 (EX1): through mixing 60% commercially available LiCoO 2(sample REF1) and 40%MOOH hybrid transition metal hydroxide and Li 2CO 3, the preparation cathode powder.Li 2CO 3: MOOH ratio and mixed hydroxides and be used to prepare REF2-LiM ' O 2Identical.Total composition of cathode powder is LiM ' O 2, M '=Co wherein 0.68Ni 0.21Mn 0.11, identical with total composition of CX2 and CX3.This mixture of heating is 8 hours in 970 ℃ of air, produces sample EX1.
The preparation button cell.The measured X x ray diffration pattern x, and carry out Rietveld and purify.Take scanning electron microscopy.Fig. 3 a has showed the scanning electron microscopy of sample EX1.Multiplication factor is 5000x.There is two types particle: (a) phase 1: fine and close erose LiCoO 2The base particle has specific island form and (b) mutually 2: Conglobation type LiM ' O 2Particle: elementary crystallite dimension has the distribution of widening.Known diagram among Fig. 3 c mutually 1.EDS analyzes (seeing below) and stresses at modification LiCoO 2There is Mn in the island on the particle surface.
Character such as cyclical stability and speed ability are more much better than imaginary sample CC1, if compare obvious improvement with CX3 with sample CX2.Scanning electron microscopy alleged occurrence LiCoO 2The island form of particle.Rietveld purifies and confirms 1 (LiCoO mutually 2) lattice constant during heating treatment do not change, but mutually 2 (LiM ' O 2) lattice constant significant change.LiM ' O 2Lattice constant change proof and between 1 and mutually 2 obvious cation exchange taking place mutually.
Embodiment E X2 and EX3: be similar to EX1 preparation and the research cathode powder of embodiment 1, except sintering temperature is respectively 960 and 950 ℃ (sintering times: 8 hours).Fig. 3 b has showed the scanning electron microscopy of sample EX3.Fig. 4 has showed the scanning electron microscopy of two phases of sample EX2: left figure has showed main phase 2 particles, and right figure mainly is phase 1 particle, can find out wherein that in addition smaller phase 2 aggregates of 1 particle are much bigger mutually.
In addition, character such as cyclical stability and speed ability are more much better than imaginary sample CC1, if compare obvious improvement with CX3 with sample CX2.
Scanning electron microscopy confirms LiCoO 2There is the island form in particle.Rierveld purifies and confirms LiCoO 2Lattice constant during heating treatment do not change, but LiM ' O 2The lattice constant of phase changes obviously.EX1,2 and 3 relatively can sum up in this variation of higher temperature more obviously, shows that (a) diffuses into LiM ' O 2Co amount along with temperature increases, but (b) character of improving depends on LiM ' O insensitively simultaneously 2Co amount mutually.
The EDS of sample analyzes
Use energy dissipation x-ray spectrometry (EDS), can study sample CX2 and the LiCoO of CX3 (comparative example) and embodiment E X1 2(phase 1) and LiM ' O 2The composition of (phase 2).
It is the effective tool that research is formed near surface particles that EDS analyzes.EDS helps monitoring to change and trend especially, but it is bad to obtain quantitative result accurately.Table 4 has been listed the EDS analysis result of reference sample REF1 and REF2, and this is used as the more datum mark of the EDS analysis of complex sample CX2, CX3 and EX1.
With EDS spectral investigation sample REF1 (LiCoO 2).Collection is from the spectrum of many particle sizings.Multiplication factor is 1000x, has showed the zone of scanning among Fig. 1.Collected the similar EDS spectrum of sample REF2 with the 1000x multiplication factor.
The levels of transition metals of table 4:ICP and EDS measure R EF1 and 2
Sample Form (by ICP) Levels of transition metals (by the mol% of EDS) Impurity (by the mol% of EDS)
REF1 Li 1.02Co Mn：0.00 Co：99.56 Ni：0.00 SO 4：0.44
REF2 Li∶M’＝0.97 M’＝ Co 0.21Mn 0.264Ni 0.526 SO 4∶M＝0.009 Mn：27.34 Co：20.72 Ni：50.39 SO 4：1.55
Relatively analyze the result who obtains, EDS is described from ICP chemical analysis and EDS
(1) measuring the transition metal ratio is in the main true
(2) exaggerative sulfur content (sulphur impurity possibly be positioned at the surface)
Analyze research cathode sample EX1 through individual particle being carried out EDS.Obtain 6 not EDS spectrum of homophase 1 particle.All particle has been showed the island form.Fig. 5 has showed the scanning electron microscopy of these 6 particles.
EDS analyzes the clear 1 (LiCoO mutually that shows 2) particle comprises (＞15%) nickel and manganese in a large number, (referring to following table 5).This is very surprising, shows mutually to have and LiCoO for 1 (comprising Ni and Mn) because the Rietveld of X-ray diffractogram purifies 2Identical lattice constant.In addition, in 6 particles 5 have and be higher than 3.0 Ni: the Mn ratio.This shows than the more nickel of manganese and diffuses into first phase.During the sintering, cation exchange takes place, wherein most of nickel and manganese are from LiM ' O 2Particle gets into LiCoO 2Particle.EDS analyzes and confirms the first phase (LiCoO in addition 2) particle have the composition that form to change along with transition metal and distribute.
Table 5:EDS measures the levels of transition metals of EX1 particle
Sample EX1 Ni (mol％) Mn (mol％) Co (mol％) Ni: Mm mol ratio (Ni+Mn)/M mol ratio (%)
Particle #1 14.01 3.22 82.77 4.35 17
Particle #2 13.74 3.47 82.78 3.96 17
Particle #3 18.67 5.42 75.9 3.44 24
Particle #4 10.62 5.54 83.46 1.92 16
Particle #5 17.46 4.77 77.57 3.66 22
Particle #6 18.49 6.07 75.25 3.05 25
With 2 particles (particle #1 and particle #2) in 6 particles in the EDS figure research table 5.The EDS of particle #1 figure shows that " island " has higher manganese content among Fig. 6, yet regional between the island, and " ocean " (or main body) has low manganese content.EDS analyzes further research particle #4 and #6 (referring to table 6) with point.Fig. 7 has showed the position of these points.Bleeding point spectrum.
Table 6:EDS measures the levels of transition metals of EX1 particle zones of different
Sample EX1 The ocean, island Ni (mol％) Mn (mol％) Co (mol％) Ni: Mm mol ratio (Ni+Mn)/M mol ratio (%)
Particle #4 point X2 I 5.91 8.27 85.75 0.71 14
Point X4 I 7.39 7.66 84.92 0.96 15
Point X5 O 2.97 1.98 95.05 1.50 5
Particle #6 point X6 I 21.75 8.62 69.63 2.52 30
Point X7 I 20.80 12.88 66.27 1.61 34
Point X8 O 11.43 1.55 87.02 7.37 13
Point X9 O 14.48 1.92 83.34 7.54 16
All " island " point (X2, X4, X6, X7) has the Ni that is starkly lower than whole particles: Mn ratio (table 5).All " ocean " point (X5, X8, X9) has the manganese content more much lower than whole particles.This embodiment confirms that the particle with island form has high Mn content in most of island, have low manganese content between the island.Obviously have the manganese gradual change, the island is the gradual change center.
Collection sample EX1 second phase (LiM ' O 2) the EDS spectrum of 3 individual particles.These particles are obtained from MOOH, and it has the metal identical with sample REF2 forms, and Ni: the Mn ratio is near 2.0, and cobalt content is near 20%.Fig. 8 has showed scanning electron microscopy.These three particles obviously have different size crystal grain.Particle 1 (left side) has the crystal grain near 0.5-1.5 μ m; Particle 2 (centre) has the crystal grain near 1-2 μ m, and particle 3 (the right) has the crystal grain near 1.5-3 μ m.Similarly, collect the single LiM ' O of sample CX2 and CX3 2The EDS spectrum of particle (phase 2).All the result lists in table 7.
Table 7: second phase (LiM ' O 2) the EDS of levels of transition metals measure
Sample Ni (mol％) Mn (mol％) Co (mol％) Ni: Mn mol ratio (Ni+Mn)/M mol ratio (%)
The many particles of REF2 50.39 27.34 20.72 1.84 79
CX2 particle 1 49.34 26.09 24.19 1.89 76
Particle 2 49.34 25.40 23.39 1.94 76
CX3 particle 1 49.14 26.58 23.03 1.85 77
Particle 2 47.34 25.86 26.22 1.83 74
EX1 particle 1 41.18 22.32 36.13 1.84 64
Particle 2 39.49 21.80 38.18 1.81 62
Particle 3 37.38 20.08 42.19 1.86 58
The sample EX1 second phase LiM ' O 2The cobalt content of particle obviously increases during sintering.This is the LiM ' O with sample CX2 and CX3 2Particle result's stark contrast, the EDS spectrum of itself and sample REF2 is roughly the same.Cation exchange takes place during showing the EX1 sintering in this observation, and wherein cobalt is from LiCoO 2(phase 1) gets into LiM ' O 2(phase 2) particle.In addition, in the comparison diagram 8 in scanning electron microscopy and the table data show sample EX1 mutually the elementary crystallite dimension of 2 particles be relevant with cobalt content.Obviously, along with cobalt diffuses into LiM ' O 2, LiM ' O 2Sinterability strengthen, cause crystal grain to increase quickly.
Embodiment 4: spray the precursor of milling
Through the injection mixed hydroxides MOOH that mills, preparation submicron-scale mixed hydroxides.This MOOH be used to prepare REF2-LiM ' O 2Identical.Utilize the laser diffraction measurement particle size distribution.After 3 injections were milled, 80% volume was made up of the particle that is lower than 1 micron-scale.
The commercially available LiCoO that mixes 90 weight % 2(sample REF1 has 20 micron particles), spray mill MOOH and Li for 10%3 times 2CO 3For 1 mole of injection MOOH that mills, add 0.5mol Li 2CO 3(this Li: the M ratio be used to prepare REF2-LiM ' O 2Identical.) after the mixing, 970 ℃ of sintered samples 8 hours.
With the final sample EX4 of SEM, BET surface analysis and X-ray diffraction studies.Make button cell.Measuring speed performance and cyclical stability.Fig. 9 has compared on the left side (A) commodity LiCoO 2(REF1) speed ability (cell voltage V is to capacity mAh/g), and the speed ability of (B) sample EX4 on the right.This figure has showed the curve of discharge voltage during C/10, C/5, C/2,1C, 1.5C, 2C, 3C, 5C and the 10C speed, and wherein 1C (corresponding to discharge in a hour) is defined as 160mA/g.Temperature is held constant at 24 ℃, and voltage range is 4.3-3.0V.Obviously, speed ability significantly increases.There is the island form in scanning electron microscopy (not show) clear displaying.
Research co-sintering condition
With sample EX1, EX2, the identical perparation of specimen CX5 of EX3, except the sintering temperature that is lower than 900 ℃ (sintering times: 8 hours).This sample obviously is different from EX1, EX2, EX3.The BET surface area is very big: 0.35 meters squared per gram.X-ray diffraction has been showed the phase mixture of two phases, and first has REF1-LiCoO 2Lattice constant, second has the sample of being similar to REF2-LiM ' O 2Lattice constant.Obviously, Co does not appear from phase 1 LiCoO 2Obviously diffuse into the second phase LiM ' O 2Similarly, the volume fraction of second phase is obviously littler, this diffuse into mutually 2 with Co still less (LiM ' O 2) be consistent.
Electrochemical properties relatively poor (table 3).Observe cyclical stability relatively poor (than the about soon 2-3 of sample EX1-EX3 doubly) at the 4.5V decline rate.Speed ability reduces obviously that (in 3C speed is 87.5%, compares with the 90-91% of sample EX1, EX2, EX3.Speed ability is similar to sample CX3.Scanning electron microscopy (not show) has been showed and has been connected big LiCoO 2Lip-deep some little LiM ' O 2Particle, but the island form do not had basically.
Identical with embodiment 4 cathode powder, make and analyze cathode powder CX6.Yet, use and the second LiM ' O mutually 2 Different precursors.Mix 90%REF1 LiCoO among this embodiment 2With 10% jet grinding precursor and 0.05mol%Li 2CO 3Precursor is the Li that lithium lacks 1-xM 1+xO 2Be similar to REF2-LiM ' O 2Make this precursor, except Li: the M ratio is 0.9, and temperature is outside 900 ℃.After the preparation, jet grinding precursor twice produces the submicron particles product.In water, utilize the laser diffraction measurement particle size distribution.This particle size distribution is a bimodal, and about 50% volume has the size of 0.05-1 μ m (maximum near 0.3 μ m), and all the other 50% volumes have the size of 1-6 μ m (maximum near 2 μ m).In 970 ℃ of air, added hot mixt 8 hours.The measured X x ray diffration pattern x, and carry out Rietveld and purify.Take scanning electron microscopy.Make button cell.
This ray diffraction pattern has showed that single-phase basically lattice constant is similar to LiCoO 2Can not obviously distinguish the 2nd LiM ' O 2(this is different from the sample of embodiment 4, and it obviously shows existence second phase).Figure 10 b has showed scanning electron microscopy.LiM ' the O that has the type of seldom reuniting 2Particle (=phase 2).Nearly all particle is LiCoO 2Base (=phase 1).These particles have very smooth surface usually.Obviously, there is not the island form.Consistent with this observation is to observe the only low-down BET surface area of 0.14 meters squared per gram.
Obviously, than sample EX4 sintered sample CX6 more effectively.Cobalt is from phase 1 LiCoO too much 2Diffuse into 2 LiM ' O mutually 2Simultaneously, little LiM ' O 2Particle is by bigger LiCoO 2Particle consumes, and LiCoO 2Middle manganese cation maybe be diluted, and the result does not have the island form.Mutually 2 with 1 composition is effectively approaching each other mutually.Second phase, even comprise more most negative electrode under the sintered sample situation than still less be similar to very much mutually 1 now, and this phase for example can not be distinguished clearly with X ray.
Electrochemical test shows:
(a) slope of voltage curve disappearance when discharge finishes-this is consistent with phase 2
Basically there is not LiM ' O 2,
(b) speed ability is starkly lower than sample EX4,
(c) cyclical stability is relatively poor
Can draw, the island form is necessary with existence second with respect to obtaining high speed performance.In addition, there is the quite narrow window that obtains the high speed negative electrode.If sintering is strong (sample CX6) too, the island disappearance owing to the high transition metal diffusing, if sintering not enough (sample CX3 and CX4), then because transition metal diffusion deficiency would not form the island.Table 2 and 3 has been summarized the data that obtain.For correct execution technology of the present invention, need set up temperature to the sintering time matrix, the scanning electron microscopy of the product that wherein obtains has clearly demonstrated the island structure of EX 1-4.If co-sintering does not take place, clearly difference phase 2 and pure LiCoO 2, do not observe island structure.If too strong co-sintering, 2 near disappearing mutually, and the Li-Co-Ni-Mn oxide that obtains has the smooth surface of circular edge.
If there are two phase LiCoO 2And LiM ' O 2, the lattice constant of the sample that can measure in addition, and with reference sample relatively, wherein reference sample is that the sintered compound that only obtains with the phase 2 required precursors that obtain (does not have LiCoO 2Or corresponding cobalt precursors).Relation between the lattice constant that obtains should be in restriction before.
The substoichiometric influence
The following example (EX5A to F) shows if sample has slight substoichiometric lithium, can further improve chemical property.Identical preparation sample with sample EX4 is except adding still less Li 2CO 3, sometimes sintering temperature raises a little.
Under any circumstance mix 90%20 μ m LiCoO 2(=REF1) and 10% jet grinding MOOH and Li 2CO 3Provide Li (Li in the following table 8 2CO 3In) with the molar ratio of MOOH.Table 8 is listed the result that sintering temperature and BET surface area measure in addition.Li: the M hurdle provides the lithium that the chemical analysis final sample obtains and the result of transition metal ratio.Chemical analysis results is similar to desired value very much, has the Li near 1.02: Co if remember sample REF1, and depends on temperature, lithium in small amounts evaporation all the time during the sample preparation.Obviously the lithium substoichiometric of sample EX5D, EX5E and EX5F increases.Carry out scanning electron microscopy analysis, confirm that whole 6 samples show island structure.The scanning electron microscopy that has represented sample EX5E among Figure 10 a.Under any circumstance X-ray analysis shows two phase amalgams (as follows).
Table 8: analyze substoichiometric sample (sintering time: 8 hours)
Li∶M T BET m 2/g Li: M chemical analysis
EX5A 0.98 970℃ 0.19
EX5B 0.96 970℃ 0.21
EX5C 0.85 970℃ 0.22 1.0
EX5D 0.7 970℃ 0.23 0.991
EX5E 0.7 985℃ 0.20 0.986
EX5F 0.65 985℃ 0.21 0.972
With with said similar condition preparation before and test button cell.The result is summarized in following table 9.
Obtain electrochemical data from two groups of two button cells.Utilize two batteries of cyclical stability program test first series.Utilize another series of speed ability program test.The cyclical stability program provides following numerical value: Qrev, Qirr, the rate of decay (C/10) and the rate of decay (C1), lists in table 3 and 9.Said electrochemical data is the mean value of two batteries of each series.Qrev and Qirr are reversibility (mAh/g) and irreversible performance (%, the Qirr [QCh-QDC]/QCh) in first circulation of C/10 tachometric survey.Discharge capacity through relatively circulating at slow (C/10) the 3rd and the 41st obtains the rate of decay numerical value at C/10, through comparing the 1C rate of decay in the discharge capacity acquisition of faster (1C) the 4th and the 42nd circulation.From circulating 5 to 40, charge and C/2 discharge rate cycle battery with C/5 at 4.5-3.0V.The rate of decay is extrapolated to 100 circulations.
The speed ability program provides the numerical value of the speed ability of numerical value 1C/0.1C, 2C/0.1C and 3C/0.1C, lists in table 3 and 9.Said program is described below.1 slowly after the circulation (C/10), at the C/5 speed said battery that charges, and in (C/5, C/2,1C, 1.5C, 2C, 3C, 5C and the 10C) discharge down that gathers way.Voltage range is 4.3-3.0V.
For with high reliability measuring capacity and speed ability, electrode load (gram/square centimeter) difference of battery.The battery that is used for stable program test has the electrode load near 12 milligrams/square centimeter.Battery with the speed program test has the load of approaching 5-6 milligram/square centimeter.
Table 9: the electrochemical data of substoichiometric sample
Q rev 4.3-3V C/10 Q irr (％) 1C/0.1C (％) 2C/0.1C (％) 3C/0.1C (％) Fading rate C/10 %/100 Fading rate C/1 %/100
EX5A 156.9 3.92 95.39 93.74 92.49 8.84 15.19
EX5B 157.1 3.79 95.98 94.25 92.84 8.34 13.80
EX5C 157.3 4.32 95.76 93.66 91.49 11.06 24.66
EX5D 156.5 4.89 96.56 94.98 93.62 6.76 12.47
EX5E 156.5 4.71 96.67 95.21 94.16 5.19 7.03
EX5F 153.7 5.84 95.57 91.86 88.42 6.69 15.01
Data show if Li in the table: the M ratio reduces, and speed ability increases.Obtain maximum speed near the substoichiometric sample of 1.5% lithium.Simultaneously, the substoichiometric sample EX5E of 1.5% lithium is further illustrated in the highest cyclical stability of 4.5V.Yet, if the lithium substoichiometric is too big, degradation.Therefore relatively poor near the capacity of the substoichiometric sample EX5F of 3% lithium, and the non-constant of speed ability.
Table 1: sample general introduction (title, composition and preparation)
The sample name Form (always) sintering T Precursor Remarks
REF1 LiCoO 2， ≈1000℃ D50≈20μm
REF2 LiNi 0.53Mn 0.27Co 0.2O 2， 950℃ MOOH，Li 2CO 3，
Calculate embodiment 1 CC1 LiCo 0.68Ni 0.21Mn 0.11O 2， n/a - 60%REF1, the average weight of 40%REF2
Comparative Examples 2 CX2 LiCo 0.68Ni 0.21Mn 0.11O 2， n/a LiCoO 2， LiNi 0.53Mn 0.27Co 0.2， Preheating LiCoO 2And LiM ' O 2Mixture
Comparative Examples 3 CX3 LiCo 0.68Ni 0.21Mn 0.11O 2， 850℃ LiCoO 2， LiNi 0.53Mn 0.27Co 0.2， LiCoO 2And LiM ' O 2Add hot mixt
Comparative Examples 4 CX4 LiCo 0.68Ni 0.21Mn 0.11O 2， 900℃ LiCoO 2， LiNi 0.53Mn 0.27Co 0.2， LiCoO 2And LiM ' O 2Add hot mixt
Comparative Examples 5 CX5 LiCo 0.68Ni 0.21Mn 0.11O 2， 900℃ LiCoO 2，MOOH Li 2CO 3 LiCoO 2, MOOH and Li 2CO 3Add hot mixt
Comparative Examples 6 CX6 LiCo 0.91Ni 0.06Mn 0.03O 2， 970℃ LiCoO 2，Li 2CO 3 Li 0.9Ni 0.53Mn 0.27Co 0 .2O 2， LiCoO 2, T LiM ' O is hanged down in jet grinding 2And Li 2CO 3Add hot mixt
Embodiment 1 EX1 LiCo 0.68Ni 0.21Mn 0.11O 2， 970℃ LiCoO 2，MOOH Li 2CO 3 LiCoO 2, MOOH and Li 2CO 3Add hot mixt
Embodiment 2 EX2 LiCo 0.68Ni 0.21Mn 0.11O 2， 960℃ LiCoO 2，MOOH Li 2CO 3 LiCoO 2, MOOH and Li 2CO 3Add hot mixt
Embodiment 3 EX3 LiCo 0.68Ni 0.21Mn 0.11O 2， 950℃ LiCoO 2，MOOH Li 2CO 3 LiCoO 2, MOOH and Li 2CO 3Add hot mixt
Embodiment 4 EX4 LiCo 0.91Ni 0.06Mn 0.03O 2， 970℃ LiCoO 2，MOOH Li 2CO 3 LiCoO 2, jet grinding MOOH and Li 2CO 3Add hot mixt
Embodiment 5 EX5A- EX5F Li xCo 0.91Ni 0.06Mn 0.03O 2 ，970-985℃ LiCoO 2，MOOH Li 2CO 3 LiCoO 2, jet grinding MOOH and Li 2CO 3Add hot mixt
Crystallization figure
Obtain reference sample REF1, REF2, the X-ray diffractogram of comparative sample CX2-CX3 and sample EX1-3.Sample CX2, CX3, EX1-EX3 are by two phase compositions, and first based on LiCoO 2, second based on LiM ' O 2Purify to obtain the lattice constant of these phases through two-phase Rietveld, and can with the sample REF1 (LiCoO that obtains through single-phase purification 2) and REF2 (LiM ' O 2) lattice constant relatively.
Table 2 is enumerated said result.Figure 11 has showed the result with suitable method, and the author is called crystallization figure, and mapping hexagon c axle is to hexagon a-axle.This figure provides the crystallization figure of sample REF1, REF2, CX2, CX3, EX1, EX2 and EX3.Inlet has been showed the zonule drawing with rectangle marked, amplification.Table 2 and Figure 11 most clearly explained sample EX1, EX2 and EX3 mutually 2 (LiM ' O 2) lattice constant distance R EF2 value have obvious variation, and 2 lattice constant is identical with REF2 mutually among the CX2, CX3.This variation is more obvious with the sintering temperature increase.Increasing sintering temperature causes the figure position to shift to LiCoO 2, leave the REF2 position of expectation.This figure goes up change in location for LiCoO 2And LiM ' O 2Between solid solution be typical.Obviously cobalt is from phase 1 (LiCoO 2) diffuse into mutually 2 (LiM ' O 2) particle.
Surprisingly, during the sintering, phase 1 (LiCoO 2) lattice constant do not change.All sample CX2, CX3 have the lattice constant identical with REF1 with EX1, EX2 and EX3.
Also generation part of Rietveld purification phase 2 (LiM ' O 2), list in table 2.Phase 2 marks increased during these data showed sintering.LiM ' the O of sample CX2 2Mark should be 40%.Obviously Rietveld is for LiM ' O 2Produce bigger value mutually.This mistake may be due to during the X ray sample preparation, granule (phase 2, LiM ' O 2) with bulky grain (mutually 1, LiCoO 2) permutatation, it can cause mutually 1 in the near surface enrichment.The preferred orientation of 1 particle can strengthen this effect mutually.Yet, ignoring this mistake, we observe trend clearly.LiM ' O 2Mark increase with sintering temperature.It shows during the sintering that more Co are from phase 1 (LiCoO 2) diffuse into mutually 2, with respect to Ni (with Mn) from 2 diffusing into phase 1 mutually.
Figure 12 has showed to have sample EX4, EX5A-EX5F and CX5, and the crystallization figure of sample REF1, REF2 data point.Utilize two-phase Rietveld to purify and obtain data point.This figure clearly illustrate that EX4, EX5A-EX5F phase 2 (LiM ' O 2) lattice constant at LiCoO 2-REF1 and REF2-LiM ' O 2Between.This diffuses into second mutually identical with the Co that discusses.1 lattice constant does not change at all mutually simultaneously, and and REF1-LiCoO 2Identical.
Figure 12 has compared sample CX5 and sample EX4, EX5A-F also according to position on the crystallization figure.The lattice constant that can sum up CX5 phase 2 is identical with REF2.This meets the phase 1 that reduces the sintering temperature generation and the cation exchange between 2 is not enough mutually.
X-ray diffractogram
Sample REF 1 and REF2 have high-crystallinity, so their X-ray diffractogram has sharp-pointed diffraction maximum.Figure 13 has showed the X-ray diffractogram (matrix: angle of scattering (degree)) of CX2, CX4, CX5 and EX1.All these samples have identical total composition.The inlet of Figure 13 has been showed with the magnification region of rectangle marked and has been mapped again.As expect, show the X-ray diffractogram that is higher than REF 1 and REF2 figure position for the sample CX2 of (heat treated) REF1 and REF2 amalgam.Even at 900 ℃ of heat treatment amalgams (sample CX4) or LiCoO 2Amalgam, mixed hydroxides and Li 2CO 3(CX5), X-ray diffractogram keeps basic identical.This tells us the first phase LiCoO 2With the second LiM ' O mutually 2Do not change.
Yet this situation is obviously different with typical sample of the present invention.Figure 13 has showed peak and the peak value alteration of form of sample EX1.Phase 1 (LiCoO 2Base) peak value keeps quite sharp-pointed sample, and the position is identical, however phase 2 (LiM ' O 2Base) peak value obviously broadens, and obviously move its position.This main cause that broadens is the stoichiometric distribution of Co and Ni.During the sintering, second phase is left in the Ni diffusion, and cobalt diffuses into second phase.As a result, variable grain and/or crystal grain have the different chemical metering, and each stoichiometry has the peak of oneself, thereby observes wideer diffraction maximum.During Rietveld purifies, the distribution that is difficult to simulate lattice constant.Yet quite fortunately, small crystalline size produces similar spectrum peak broadening to a certain extent.Negative electrode typical R ietveld therefore of the present invention purifies and shows the first phase (LiCoO 2Base) be big crystallite dimension, and second phase (LiM ' O 2) crystallite dimension is much little.Simultaneously, the peak of the second phase diffraction maximum is towards a LiCoO 2Obviously move the position of phase.
Figure 14 has showed the X-ray diffractogram of sample CX6 and EX9E.All these samples have identical total composition.Sample CX6 is different from sample as stated.The sample sintering is too strong.Therefore diffusion is carried out excessively.Second become mutually and be similar to first phase as a result, and can not use their X ray picture difference.The whole of maintenance are that the small shoulder in phase 1 peak is towards low angle.In contrast, but sample EX9E has showed little clearly peak value at low angle.Among Figure 14 with some such peaks of arrow labeled.
In contrast, but sample EX9E has showed little clearly peak at low angle.Get into second phase if we understand Co, it measures increase, and its lattice constant is towards LiCoO 2Lattice constant (referring to top) move, so the X ray peak moves more approachingly, overlapping and last coincidence.Therefore excessively the middle mutually phase 2 of sintering possibly not disappear, but becomes too similar, with LiCoO 2Different.
Can sum up negative electrode of the present invention shows near the LiCoO with high-crystallinity 2The X ray picture of figure, and LiM ' O with low-crystallinity 2Figure.Degree of crystallinity still quite is suitable for two phases.Some commercial cathode materials are than 2 still less crystallizations mutually.In addition, the lattice constant of second phase is lower than desired value (this peak is more near LiCoO 2The peak); Desired value is the LiM ' O from identical MOOH precursor preparation 2The representative value of phase.
Table 2 has been summarized the result that Rietveld purifies.
Table 2:BET surface area and crystallization data
Figure G2008800034640D00301
Voltage curve
Prepare button cell from whole reference sample REF1, REF2, whole comparative sample CX2, CX3 and EX1, EX2 and EX3.Showed slow interdischarge interval among Figure 15, the voltage curve of CX2, CX3 and EX1-EX3.Sample CX2 and CX3 have showed platform clearly at 3.88V.This platform is for LiCoO 2Be typical.The existence of this platform shows that phase 1 is pure LiCoO 2Yet for sample EX1, EX2 and EX3, along with sintering temperature increases, this platform fades away.Obviously, phase 1 does not have LiCoO 2This coincide with the fact that 1 particle mutually comprises Ni and Mn, analyzes like EDS clearly to show.Yet very surprisingly, 1 has LiCoO mutually 2Definite X-ray diffractogram, its lattice constant obviously is different from Li doped CoO 2The Ni-Mn desired value.
Speed ability and cyclical stability
Table 3 has been enumerated with reference to the button cell of REF1 and REF2 and sample CX2, CX3, EX1, EX2 and EX3 and has been tested the result who obtains, and the calculated value of assumes samples CC1.All sample has identical total composition.This table provides the average data of 2 button cells of each sample.
We notice sample CX2 (heating LiCoO 2And LiM ' O 2Amalgam) have a performance that is similar to very much assumes samples.Significantly-mixing LiCoO 2And LiM ' O 2Do not produce any benefit.Sample CX3 and CX4 (heating LiCoO 2And LiM ' O 2Amalgam) have a little better speed ability and the cyclical stability that improves a little, but performance obviously different with sample CX2 or CC1 usually.
Yet sample EX1, EX2 and EX3 show the speed ability of obvious improvement.At 1C, 2C, 3C, compare with 91-93,86-88 and the 83-86% of assumes samples CC1 or amalgam CX2, or compare with 89% with 94,91 of sample CX3, obtain capacity near 95,93 and 91%.
We notice that improving speed ability does not relate to different forms.All sample CX2, CX3, EX1-3 have BET surface area much at one, among the common figure all samples are amalgams of erose particle (mutually 1) and the reunion of big densification than granule (mutually 2).In addition, particle size distribution is identical substantially.Acquisition speed increases, and not increasing the BET specific area is the very important aspect of the present invention.Basically can reduce the BET surface area satisfying fail safe and density requirements, and still obtain enough speed abilities.
Significantly improved simultaneously the cyclical stability of EX1, EX2 and EX3.Figure 16 has showed the data that sample EX1 obtains.Figure 16 a has showed that the calculated value (capacity is to cycling numerical value #) of per 100 loop attenuation speed is 6.4%.Point is represented charging capacity, a little bigger expression discharge.Figure 16 b has showed the cyclical stability of EX1.Figure 16 c has showed the speed ability of EX1.
Among Figure 17, the comparative sample CX6 (left side: A) with EX5E (the right: cycle performance B).
Table 3: the electrochemical test result is the mean value of two button cells.
The sample name Q rev 4.3-3V C/10 Q irr (％) 1C/0.1C (％) 2C/0.1C (％) 3C/0.1C (％) Fading rate C/10 %/100 Fading rate C/1 %/100
The REF1 of heating 153.8 5.3 90.9 85.3 81.6 76 171
REF2 158.2 3.1 95.6 93.1 91.0 40 110
The REF2 of heating 169.2 13.5 91.4 88.7 86.0 0.4 2.8
CC1 159.4 8.9 90.9 86.0 82.9 47 107
CX2 159.9 7.9 92.2 88.1 85.3 55.6 128
CX3 161.7 7.7 93.8 90.7 88.5 31.5 79.3
CX4 161.0 7.7 93.8 90.8 88.2 22.3 59.0
CX5 157.7 9.5 92.9 89.8 87.5 6.6 18.9
CX6 156.8 4.0 91.6 89.8 89.6 32.3 68.0
EX1 159.6 6.4 95.0 92.7 91.1 5.6 9.5
EX2 160.2 6.5 94.5 92.0 90.4 5.7 10.1
EX3 159.5 7.4 94.4 92.0 90.7 3.4 6.5
EX4 156.5 4.2 95.5 93.6 91.9 10.5 27.4
EX5A 156.9 3.9 95.4 93.7 92.5 8.8 15.2
EX5B 157.1 3.8 96.0 94.3 92.8 8.3 13.8
EX5C 157.3 4.3 95.8 93.7 91.5 11.1 24.7
EX5D 156.5 4.9 96.6 95.0 93.6 6.8 12.5
EX5E 156.5 4.7 96.7 95.2 94.2 5.2 7.0
EX5F 153.7 5.8 95.6 91.9 88.4 6.7 15.0

Claims (23)

1. powder lithium transition-metal oxide, it comprises first phase, and this is first by the LiCoO that contains Mn and Ni 2Particle is formed, and said particle has Mn and Ni enrichment island in its surface, and comprises the second no island phase, and this second no island has general formula Li mutually 1+aM ' 1-aO 2 ± b, wherein-0.03＜a＜0.05, and b＜0.02, M '=Ni mMn nCo 1-m-n, wherein m>=n, and 0.1＜m+n＜0.9, the Mn on said island and Ni concentration are higher than Mn and the Ni concentration in the said particle body, and said island comprises Mn and said Mn of containing of Ni concentration ratio in wherein said Mn and the Ni enrichment island and the LiCoO of Ni of 5mol% at least 2The high at least 2mol% of Ni concentration in the particle body.
2. according to the said powder lithium transition-metal oxide of claim 1, it is characterized in that said Mn and Ni enrichment island have the thickness of 100nm at least, and cover the said LiCoO that contains Mn and Ni less than 70% 2The surface of particle.
3. according to claim 1 or 2 said powder lithium transition-metal oxides, the said LiCoO that contains Mn and Ni of the Mn concentration ratio in the wherein said island 2The high at least 4mol% of Mn concentration in the particle body.
4. powder lithium transition-metal oxide according to claim 1, the said LiCoO that contains Mn and Ni of Ni concentration ratio in wherein said Mn and the Ni enrichment island 2The high at least 6mol% of Ni concentration in the particle body.
5. powder lithium transition-metal oxide according to claim 1 has the LiCoO that contains Mn and Ni 2Particle wherein comprises Ni and the Mn of 3mol% at least.
6. powder lithium transition-metal oxide according to claim 1 is characterized in that the LiCoO of said Mn of containing and Ni 2The lattice constant a of particle and c are respectively 2.815+/-0.002 and 14.05+/-0.01.
7. powder lithium transition-metal oxide according to claim 1 is characterized in that containing the LiCoO of Mn and Ni 2Particle is a monoblock, and does not have internal void.
8. powder lithium transition-metal oxide according to claim 1 is characterized in that the LiCoO of said Mn of containing and Ni 2The d50 that the distribution of sizes of particle has is greater than 10 μ m.
9. powder lithium transition-metal oxide according to claim 1 comprises the said Mn of containing of 30wt% to 95wt% and the LiCoO of Ni 2Particle.
10. according to the said powder lithium transition-metal oxide of claim 1, has composition Li xM yO 2 ± δ, wherein:
0.97＜x＜1.03,0.97＜y＜1.03, x+y=2, and δ＜0.05;
And M=Co 1-f-gNi fMn g, wherein 0.05＜f+g＜0.5, and f>=g.
11. according to the said powder lithium transition-metal oxide of claim 10, it is characterized in that lattice constant a ' and the c ' of said no island phase with reference to lithium transition-metal (M Ref) the lattice constant a " and c " of corresponding no island phase of oxide has following relationship, has identical composition Li xM yO 2 ± δ, and by pure LiCoO 2Particle constitutes with said corresponding no island mutually:
0.980＜a '/a "＜0.998 and 0.9860＜c '/c "＜0.9985.
12. powder lithium transition-metal oxide according to claim 10; It is characterized in that said no island has secondary granule mutually; Its particle size distribution that has has 2 to 10 microns d50; Said secondary granule is made up of the elementary grain colony aggressiveness of sintering, and wherein the particle size distribution that has of aggregate has the d50 of 0.5 to 2 μ m.
13. powder lithium transition-metal oxide according to claim 10 it is characterized in that said Mn further comprises Ti with Ni enrichment island with said no island mutually, thereby Ti content is less than oxide Li xM yO 2 ± δThe 10mol% of middle M.
14. powder lithium transition-metal oxide according to claim 10, oxide Li xM yO 2 ± δIn, further comprise less than one or more of the M of 5mol% and be selected from the alloy of Al and Mg, and be selected from the alloy of Be, B, Ca, Zr, S, F and P less than one or more of the M of 1mol%.
15. an electrochemical cell that comprises negative electrode, wherein negative electrode comprises any one described powder lithium transition-metal oxide of claim 1 to 14 as active material.
16. a method for preparing any one said powder lithium transition-metal oxide of claim 1 to 14 comprises step:
-LiCoO is provided 2Powder or cobalt content at least 90mol% the mixture that contains cobalt precursors compound and Li-Ni-Mn-Co oxide or Ni-Mn-Co precursor powder and Li precursor compound and
-at least 910 ℃ the said mixtures of temperature T sintering, sintering time t is 1 to 48 hour,
To obtain to have in its surface the LiCoO that contains Mn and Ni on Mn and Ni enrichment island 2Particle.
17. according to the said method of claim 16, wherein the Ni-Mn-Co precursor powder is transition metal hydroxide, oxyhydroxide, carbonate, oxycarbonate or lithium transition metal compound, wherein transition metal is formed M " being M "=Ni oMn pCo 1-o-p, wherein o+p＞0.5, and o＞p.
18. according to any one described method of claim 16 to 17, wherein the Ni-Mn-Co precursor powder comprises the levels of transition metals of 5 to 70mol% said powder lithium transition-metal oxides.
19. according to claim 16 to 17 any one described method, wherein LiCoO 2Powder has the tap density of at least 2 gram/cubic centimetres, and is made up of the monoblock particle of d50 at least 10 μ m.
20. according to any one described method of claim 16 to 17, wherein containing the cobalt precursors compound is a kind of or the hydroxide of more kinds of cobalts, oxyhydroxide or carbonate.
21. according to any one described method of claim 16 to 17, wherein said LiCoO 2Or contain the transition metal that cobalt precursors comprises at least 80% said powder lithium transition-metal oxide, and the precursor powder that contains Ni-Mn-Co is made up of the particle of the particle size distribution with the d50 between 1 to the 3 μ m.
22. according to any one described method of claim 16 to 17, wherein said LiCoO 2Or contain cobalt precursors and comprise the transition metal less than 80% said powder lithium transition-metal oxide, and contain the Ni-Mn-Co precursor and constitute by the Conglobation type particle, wherein the Conglobation type particle has the particle size distribution of the d50 between 4 to the 10 μ m.
23. according to any one described method of claim 16 to 17, the precursor that wherein contains Ni-Mn-Co further comprises Ti.
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