CN115692654A

CN115692654A - Composite cathode material, preparation method thereof and lithium ion battery

Info

Publication number: CN115692654A
Application number: CN202211351396.5A
Authority: CN
Inventors: 任荃; 刘亚飞; 陈彦彬
Original assignee: Beijing Easpring Material Technology Co Ltd
Current assignee: Beijing Easpring Material Technology Co Ltd
Priority date: 2022-10-31
Filing date: 2022-10-31
Publication date: 2023-02-03

Abstract

The invention relates to the field of lithium ion batteries, and discloses a composite cathode material, a preparation method thereof and a lithium ion battery. The composite anode material comprises a multi-element material and a lithium iron manganese phosphate material; the composite cathode material has the following conditions that the FWHM (110) and the FWHM (111) of the (110) crystal plane and the FWHM (111) of the (111) crystal plane are obtained through XRD (X-ray diffraction) tests: 0.18 to 0.25,0.2 to FWHM (111) to 0.26. When the composite cathode material is subjected to an X-ray diffraction test, a special XRD spectrogram is presented, the composite cathode material has proper crystallinity, good structural stability and higher thermal stability, and when the cathode material is used for a lithium ion battery, the composite cathode material has high charge and discharge capacity, high cycle rate, long cycle life and excellent safety performance.

Description

Composite cathode material, preparation method thereof and lithium ion battery

Technical Field

The invention relates to the field of lithium ion batteries, in particular to a composite cathode material and a preparation method thereof, and a lithium ion battery.

Background

In recent years, new energy automobiles are emerging as a national strategy industry for dealing with environmental pollution and energy crisis, and show a good situation of vigorous development, and lithium ion batteries are widely applied to markets such as electric automobiles, energy storage power stations, communication and digital electronic products as new energy carriers with excellent comprehensive performance. The anode material is used as a core key material of the lithium ion battery and directly determines the technical performance level of the battery. Currently commercially available ternary positive electrode material NCM (LiNi) _x Co _y Mn _1-x-y O ₂ ) Has high specific capacity (170-210 mAh g) ^-1 ) And energy density, but the market expansion is limited by poor safety performance, and particularly, the battery stability is poor under the use condition of high-nickel materials (x is more than or equal to 0.6) or high voltage (more than or equal to 4.4V). And commercial lithium iron phosphate (LiFePO) ₄ ) In contrast to the material, lithium manganese iron phosphate (LiMn) _x Fe _1-x PO ₄ ) The material has higher Mn ²⁺ /Mn ³⁺ A voltage platform, which can provide higher energy density. The material has tetrahedral PO consisting of stronger P-O bonds ₄ The crystal structure can be effectively stabilized, and higher safety is shown.

The lithium manganese iron phosphate material and a multi-component material system have obvious differences of different electrolytes, different voltage platforms and the like in the using process, so that if the conventional lithium manganese iron phosphate material and the multi-component material are simply mixed for use, the problems of low compaction density, difficulty in compatibility of the electrolytes, overcharge of particles of the multi-component material and the like exist, the cycle life of the battery is further shortened, the gas generation is serious and the like, and the advantages of the lithium manganese iron phosphate material and the multi-component material are difficult to be considered.

CN105406069A discloses a method for coating a ternary material with lithium manganese iron phosphate. When the lithium manganese iron phosphate and the ternary material are sintered, the argon protection atmosphere required by the lithium manganese iron phosphate is adopted, but the sintering of the ternary material needs air or oxygen-enriched atmosphere, and the sintering in the inert atmosphere can lead Ni in the ternary material to be generated ³⁺ Is easy to be reduced into Ni ²⁺ And the ions are easy to migrate to the lithium position to generate cation mixing and discharging, so that the material performance is influenced, therefore, the ions and the lithium position cannot be well coordinated, and the method is not suitable for mass production.

CN108777298a discloses that the high energy density of ternary material and the strong cycling stability of lithium manganese iron phosphate are utilized, and the two are mixed in the slurry preparation process, so that the overall heat release of the anode material can be reduced, and the safety performance of the battery can be improved.

CN103474625A discloses a sol-gel method for in-situ synthesis of a layer of lithium iron phosphate on the surface of lithium nickel cobalt manganese oxide. The lithium iron phosphate layer formed on the surface of the positive electrode material can reduce the Ni content on the surface, reduce the occurrence of side reactions and improve the thermal stability of the material. The nickel-manganese element can be complexed with organic components in the sol to form a weak chemical bond effect, so that the material can be uniformly coated, but the lithium iron phosphate is synthesized in situ on the surface, the method is complex, and the purity of the lithium iron phosphate is difficult to ensure.

Therefore, a composite cathode material that can fully exert the advantages of the lithium iron manganese phosphate material and the multi-component material is needed.

Disclosure of Invention

The invention aims to overcome the problems that in the prior art, a lithium iron manganese phosphate material and a multi-component material are simply mixed, the compatibility of the two materials is poor, the advantages of the two materials are difficult to simultaneously exert, the multi-component material particles are overcharged, electrolyte is difficult to be compatible and the like, the thermal stability of a battery is further poor, the cycle life is shortened and the like, and provides a composite cathode material, a preparation method thereof and a lithium ion battery in order to take the advantages of the lithium iron manganese phosphate material and the multi-component material into consideration. When the composite cathode material is subjected to an X-ray diffraction test, a special XRD spectrogram is presented, the composite cathode material has proper crystallinity, good structural stability and higher thermal stability, and when the cathode material is used for a lithium ion battery, the composite cathode material has high charge and discharge capacity, high cycle rate, long cycle life and excellent safety performance.

In order to achieve the above object, a first aspect of the present invention provides a composite positive electrode material, which is characterized by comprising a multi-component material and a lithium iron manganese phosphate material;

the (110) crystal face of the anode material is obtained by XRD testFWHM of full width at half maximum ₍₁₁₀₎ And FWHM of full width at half maximum of (111) crystal plane ₍₁₁₁₎ The following conditions are satisfied:

0.18≤FWHM ₍₁₁₀₎ ≤0.25，0.2≤FWHM ₍₁₁₁₎ ≤0.26。

the second aspect of the present invention provides a method for preparing a composite positive electrode material, wherein the method comprises the steps of:

step 1: preparation of multicomponent materials

(1) Mixing a multi-element material precursor, a first lithium source and an optional additive N1, and performing first calcination to obtain a first calcined material;

(2) Coating the first calcined material with an optional additive N2, and then carrying out first heat treatment to obtain the multi-component material;

step 2: preparation of lithium manganese iron phosphate material

(3) Mixing and homogenizing a lithium manganese iron phosphate material precursor, a second lithium source, a first carbon source and an additive L1, drying and carrying out secondary calcination to obtain the lithium manganese iron phosphate material;

and step 3: preparation of composite cathode material

(4) Mixing the multielement material with the lithium iron manganese phosphate material, performing second heat treatment, and sieving to obtain the composite positive electrode material;

wherein, in the step (4), the conditions of the second heat treatment include: under the oxygen-containing atmosphere, the heat treatment temperature is 100-400 ℃, the heat treatment time is 1-6h, and the oxygen concentration in the oxygen-containing atmosphere is more than or equal to 8vol%.

The third aspect of the invention provides a composite cathode material prepared by the preparation method.

In a fourth aspect of the present invention, there is provided a lithium ion battery comprising the composite positive electrode material described above.

By the technical scheme, the composite cathode material, the preparation method thereof and the lithium ion battery provided by the invention have the following beneficial effects:

(1) When the composite anode material provided by the invention is subjected to an X-ray diffraction test, the composite anode material has a specific (110) crystal faceFull width at half maximum FWHM of ₍₁₁₀₎ And FWHM of full width at half maximum of (111) crystal plane ₍₁₁₁₎ With a numerical range, the composite positive electrode material having the specific crystal structure exhibits appropriate crystallinity and good structural stability.

(2) Furthermore, the composite anode material provided by the invention has the advantages that the carbon coating layer of the lithium manganese iron phosphate coated on the surfaces of the multi-component material particles provides a convenient electron transmission path, the conductive effect of the conductive carbon black in the anode plate is enhanced, and the Li conductive anode material is beneficial to Li ⁺ The migration of electrons in the insertion/extraction reaction avoids the side reaction caused by the contact of multi-component material particles and electrolyte, reduces the resistance of charges in the migration process and reduces the polarization of the battery.

(3) The composite anode material provided by the invention is subjected to heat treatment under specific conditions, so that the lithium iron manganese phosphate material only reacts with residual alkali on the surface of the multi-component material, cannot further enter crystal lattices, cannot form an internal crystal structure for blocking lithium ion shuttling, and only forms a thin coating layer on the surface of the multi-component material, so that the cycle performance is effectively improved under the condition of not reducing the capacity of the multi-component material.

(4) The preparation method provided by the invention has the advantages of simple process and no pollution; the doping element is simple in introduction mode, controllable in process and very suitable for industrial production.

(5) When the composite cathode material provided by the invention is used for a lithium ion battery, the composite cathode material has good structural stability in the charging and discharging processes, the specific discharge capacity exceeds a theoretical value, and the cycle performance is excellent. The safety performance of the battery is ensured while high charge and discharge capacity is ensured. The coated lithium iron manganese phosphate material with a stable structure delays the thermal decomposition temperature of the composite anode material, reduces the heat released by thermal runaway, improves the safety of the battery, and prolongs the cycle life of the lithium ion battery.

Drawings

FIG. 1 is a scanning electron microscope pattern magnified 10K times for the composite positive electrode material prepared in comparative example 1;

FIG. 2 is a scanning electron microscope pattern magnified by 10K times of the composite positive electrode material prepared in comparative example 4;

FIG. 3 is a scanning electron microscope pattern magnified by 10K times of the composite positive electrode material prepared in comparative example 5;

FIG. 4 is a scanning electron microscope pattern magnified 10K times for the composite positive electrode material prepared in comparative example 7;

FIG. 5 is a scanning electron microscope pattern magnified 10K times for the composite positive electrode material prepared in comparative example 8;

FIG. 6 is a scanning electron microscope pattern magnified by 10K times of the composite positive electrode material prepared in example 1;

fig. 7 is an X-ray diffraction analysis pattern of the composite positive electrode materials prepared in comparative example 1, comparative example 4, comparative example 5 and example 1;

fig. 8 is a charge and discharge curve at 0.1C for lithium ion batteries assembled from the composite positive electrode materials of comparative example 1, comparative example 4, and example 1;

fig. 9 is a graph of cycle performance at 0.1C for lithium ion batteries assembled from the composite positive electrode materials of comparative example 1, comparative example 4, and example 1;

fig. 10 is a differential scanning calorimetry plot of the composite positive electrode materials of comparative example 1 and example 1.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

The invention provides a composite anode material, which is characterized by comprising a multi-element material and a lithium iron manganese phosphate material;

the composite cathode material has a full width at half maximum (FWHM) of a (110) crystal face obtained by XRD test ₍₁₁₀₎ And FWHM of full width at half maximum of (111) crystal plane ₍₁₁₁₎ The following conditions are satisfied:

0.18≤FWHM ₍₁₁₀₎ ≤0.25，0.2≤FWHM ₍₁₁₁₎ ≤0.26。

according to the invention, the composite positive electrodeThe material obtains the full width at half maximum FWHM of the (110) crystal face through XRD test ₍₁₁₀₎ And FWHM of full width at half maximum of (111) crystal plane ₍₁₁₁₎ The following conditions are satisfied:

0.2≤FWHM ₍₁₁₀₎ ≤0.24，0.22≤FWHM ₍₁₁₁₎ ≤0.25。

in the invention, when the full width at half maximum FWHM of the (110) crystal plane of the composite cathode material is ₍₁₁₀₎ And FWHM of full width at half maximum of (111) crystal plane ₍₁₁₁₎ When the ratio satisfies the above range, the multielement material and the lithium iron manganese phosphate material are tightly combined, and the small particles are uniformly attached to the surface of the large particles, so that the composite cathode material comprising the multielement material and the lithium iron manganese phosphate material has proper crystallinity and good structural stability.

In the invention, further XRD spectrogram analysis of the composite cathode material finds that the full width at half maximum FWHM of the (110) crystal face of the composite cathode material is the FWHM ₍₁₁₀₎ And FWHM of full width at half maximum of (111) crystal plane ₍₁₁₁₎ When the composite cathode material is used in a lithium ion battery, the battery has high charge and discharge capacity, high cycle rate, long cycle life and excellent safety performance.

In particular, XRD tests were performed on the composite positive electrode material, and it was found that when the position of the characteristic diffraction peak of the composite positive electrode material was not shifted any more, and no other new diffraction peak was observed, the composite positive electrode material thus obtained exhibited suitable crystallinity and good structural stability.

Further, the composite cathode material obtains a full width at half maximum FWHM of a (110) crystal face through XRD test ₍₁₁₀₎ And FWHM of full width at half maximum of (111) crystal plane ₍₁₁₁₎ The following conditions are satisfied:

0.6≤FWHM ₍₁₁₀₎ /FWHM ₍₁₁₁₎ ≤1.1。

in the invention, the lithium iron manganese phosphate material has an olivine crystal structure, and the ternary material is alpha-NaFePO ₂ Layered crystal structure, belonging to the R3m space.

Further, the composite cathode material obtains a full width at half maximum FWHM of a (110) crystal face through XRD test ₍₁₁₀₎ And FWH half width of (111) crystal planeM ₍₁₁₁₎ The following conditions are satisfied:

0.7≤FWHM ₍₁₁₀₎ /FWHM ₍₁₁₁₎ ≤1。

according to the invention, the multielement material has a composition as shown in formula I:

Li _e (Ni _1-x-y-z-m Co _x M _y G _z R _m )O _q (PO ₄ ) _n formula I;

wherein e is more than or equal to 0.9 and less than or equal to 1.3, x is more than or equal to (1-x-y-z-m), y is more than or equal to (1-x-y-z-m), 0.5 is more than or equal to 1-x-y-z-m and is more than 1,0 and is more than or equal to 0.25,0 and is more than or equal to z and is more than 0.05,0 and is more than or equal to m and is more than 0.05,0 and is more than or equal to n and is more than or equal to 0.01, and q is (4-3 n)/2; m is selected from Al and/or Mn element, G is selected from at least one element in the IIA-IIIA groups of the 2-5 periods, R is selected from at least one element of B, mg, ca, sr, Y, ti, V, cr, fe, cu, zr, W, nb and Al.

In the present invention, according to O ^2- And PO ₄ ^3- The valence calculation of (c) needs to satisfy 2 q + 3n =4.

According to the invention, the specific doping elements G and R are selected for the multi-component material, so that different bonding is formed between the transition metal and different doping elements in the multi-component material, and further, the battery prepared from the anode material has high first charge-discharge capacity and excellent cycle performance.

Furthermore, e is more than or equal to 0.95 and less than or equal to 1.2, x is more than or equal to (1-x-y-z-m), y is more than or equal to (1-x-y-z-m), 0.6 is more than or equal to 1-x-y-z-m and is more than or equal to 0.9,0.05 and is more than or equal to 0.2,0.01 and is more than or equal to z is more than or equal to 0.03,0.01 and is more than or equal to m and is more than 0.03,0 and is more than or equal to n and is more than or equal to 0.007, and q is (4-3 n)/2; g is at least one element selected from Al, mg, ca, sr, zr, nb and Mo.

According to the invention, the lithium iron manganese phosphate material has a composition represented by formula II:

Li _i Mn _1-h-k-j Fe _h D _k D′ _j (PO ₄ ) /C formula II;

wherein h is more than 0.1 and less than or equal to 0.4,0 and more than or equal to 0.04,0 and more than j is less than or equal to 0.04,0.9 and more than i is less than or equal to 1.2; d is selected from at least one element of Mg, co, ni, cu, zn and Ti, D' is selected from at least one element of Mg, ca, sr, ti, V, cr, co, ni, cu, zn, zr, Y, mo, nb, B, al, W, la and Sm, and the weight of the carbon element is 5-12 percent based on the total weight of the lithium iron manganese phosphate material.

According to the invention, the doping elements D and D' can stabilize the material structure, weaken the interaction of Li-O bonds, improve the ion diffusion coefficient and achieve the effects of improving the capacity, multiplying power and cycle performance of the battery; furthermore, the overall conductivity of the carbon-coated iron manganese phosphate material is enhanced, so that a convenient electron transmission path is provided, charge transmission and lithium ion diffusion are facilitated, and the capacity of the multi-element material is favorably exerted.

Furthermore, h is more than 0.15 and less than or equal to 0.35,0.01 and less than or equal to 0.03,0.01 and less than or equal to j is more than or equal to 0.03,1 and i is more than or equal to 1.1; d is at least one element selected from Mg, cu and Ti; d' is at least one element selected from Ti, nb and B, wherein the weight ratio of the carbon element is 8-10% based on the total weight of the lithium iron manganese phosphate material.

According to the present invention, the composite positive electrode material has an average particle diameter D ₅₀ Is 1-20 μm, preferably D ₅₀ Is 2-10 μm.

According to the invention, the composite anode material is a composite anode material which takes a multi-element material as a core and takes lithium iron manganese phosphate as a coating layer.

In the invention, the inventor discovers through XRD test that the lithium iron manganese phosphate material serving as the coating layer in the composite anode material provided by the invention does not enter the crystal lattice of the multi-element material, so that the structure of the multi-element material is not changed, and the stability and the safety of the composite anode material in the circulating process are improved under the condition that the capacity of the multi-element material is not influenced. According to the invention, the coated lithium iron manganese phosphate material can prevent direct contact between the multi-component material and the organic electrolyte, so that the probability of side reaction of the multi-component material and the organic electrolyte is reduced, and the stability and safety of the composite anode material in the circulating process are enhanced.

According to the invention, the average particle size D of the said multicomponent material ₅₀ Is 1-20 μm, preferably 2-10 μm.

According to the invention, the average thickness of the lithium iron manganese phosphate material coating layer is 10-400nm, preferably 50-300nm.

According to the invention, the weight ratio of the multi-component material to the lithium iron manganese phosphate material is 1-9:1, preferably 1.5-4:1, based on the total weight of the composite cathode material.

step 1: preparation of multicomponent materials

(2) Coating the first calcined material with an optional additive N2, and then carrying out first heat treatment to obtain the multi-element material;

step 2: preparation of lithium manganese iron phosphate material

and step 3: preparation of composite cathode material

The inventor of the invention researches and discovers that the advantages of the multielement material and the lithium iron manganese phosphate material cannot be fully combined by mixing the multielement material and the lithium iron manganese phosphate material according to the conventional method, and the problems of low compacted density, difficult compatibility of electrolyte, overcharge of multielement material particles and the like exist.

Through heat treatment under specific conditions, the lithium iron manganese phosphate material only reacts with residual alkali on the surface of the multi-component material, and cannot further enter the crystal lattice, an internal crystal structure for blocking shuttle of lithium ions cannot be formed, and a thin coating layer is only formed on the surface of the multi-component material, so that the cycle performance is effectively improved under the condition that the capacity of the multi-component material is not reduced.

More importantly, the composite cathode material of the first aspect of the invention can be prepared by the method provided by the invention, and specifically, the composite cathode material has a full width at half maximum (FWHM) of a (110) crystal face when subjected to XRD (X-ray diffraction) test ₍₁₁₀₎ And FWHM of full width at half maximum of (111) crystal plane ₍₁₁₁₎ The composite cathode material meets a specific range, and when the composite cathode material is used for a lithium ion battery, the battery has high charge and discharge capacity, high cycle rate, long cycle life and excellent safety performance.

In the preparation process of the composite cathode material, the mixture containing the multi-element material and the lithium iron manganese phosphate material is subjected to second heat treatment. The specific conditions of the second heat treatment are favorable for improving the reaction activity of the anode material, the close contact between the multi-element material and the lithium iron manganese phosphate material, the particle size distribution of the secondary particles is optimized, and the rate capability and the cycle performance are effectively improved. Performing the second heat treatment in an oxygen-containing atmosphere to prevent Ni from being generated during the heat treatment ³⁺ Is reduced to Ni ²⁺ And the ions migrate to the lithium position to generate cation mixing and discharging, so that the performance of the material is influenced.

Furthermore, the preparation method provided by the invention has the advantages of simple process and no pollution; the doping element is simple in introduction mode, controllable in process and very suitable for industrial production.

In the invention, the XRD spectrogram of the composite anode material is observed, the position of the characteristic diffraction peak of the composite anode material is not shifted, which indicates that the crystal structures of the two materials are not changed in the mixing process; no other new diffraction peak was observed, indicating that no hetero-phase material was produced during the preparation of the composite positive electrode material.

According to the present invention, further, in the step (4), the conditions of the second heat treatment include: under the oxygen-containing atmosphere, the heat treatment temperature is 150-300 ℃, the heat treatment time is 2-4h, and the oxygen concentration in the oxygen-containing atmosphere is more than or equal to 8vol%.

According to the invention, in the step (4), the mechanical mixing equipment adopted in the mixing process is one of a ball mill tank, a stirring mill and a high-speed mixer.

In the present invention, the stirring speed during the mixing process is 100 to 3000rpm, preferably 400 to 2000rpm.

According to the invention, the lithium manganese iron phosphate is uniformly coated on the surfaces of the multi-component material particles by adopting mechanical mixing equipment, so that the direct contact between the multi-component material and the organic electrolyte can be prevented, the probability of side reaction of the multi-component material and the organic electrolyte is reduced, and the stability and the safety of the composite anode material in the circulating process are enhanced.

According to the invention, the optional additive N1 is a compound containing a doping element G selected from at least one element of groups IIA-IIIA of periods 2-5.

Further, the doping element G is at least one element selected from Al, mg, ca, sr, zr, nb and Mo.

In the present invention, the specific type of the doping element G-containing compound is not particularly limited, and may be, for example, at least one of an oxide, a carbonate, a fluoride, a boride, a hydroxide, a sulfate, a nitrate, and a chloride, and preferably at least one of a sulfate, a nitrate, and a chloride.

According to the invention, the optional additive N2 is a compound containing a doping element R selected from at least one element of the group consisting of B, mg, ca, sr, Y, ti, V, cr, fe, cu, zr, W, nb and Al.

In the present invention, the specific type of the doping element R-containing compound is not particularly limited, and may be at least one of an oxide, a carbonate, a fluoride, a boride, a hydroxide, a sulfate, a nitrate, and a chloride, and preferably at least one of a sulfate, a nitrate, and a chloride.

According to the invention, the first carbon source is selected from at least one of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol and dopamine.

Further, the first carbon source is selected from at least one of glucose, sucrose, starch, and cellulose.

According to the invention, the added first carbon source is subjected to ingredient sintering in a manner of doping and coating carbon, so that doping of different elements and coating of different carbon sources can be realized, the electronic conductivity can be improved, and the electrochemical performance of the material can be further improved.

According to the invention, the additive L1 is a compound containing a doping element D' selected from at least one of the elements Mg, ca, sr, ti, V, cr, co, ni, cu, zn, zr, Y, mo, nb, B, al, W, la and Sm.

Further, the doping element D' is at least one element selected from Ti, nb, and B.

In the present invention, the specific type of the doping element D' containing compound is not particularly limited, and may be at least one of an oxide, a carbonate, a fluoride, a boride, a hydroxide, a sulfate, a nitrate and a chloride, and preferably at least one of a sulfate, a nitrate and a chloride.

In the present invention, the kind of the first lithium source and the second lithium source is not particularly limited, and may be a lithium source that is conventional in the art, for example, at least one selected from lithium carbonate, lithium hydroxide, lithium fluoride, lithium chloride, and lithium nitrate, and the first lithium source and the second lithium source may be the same or different.

In the present invention, the solvent of the solution is water, unless otherwise specified.

In the invention, the multi-element material precursor contains Ni, co and M elements, wherein M is selected from Al and/or Mn elements.

According to the invention, in step (1), the multielement material is calculated as [ n (Ni) + n (Co) + n (M) ], the first lithium source is calculated as n (Li), and the first lithium source is used in an amount such that 0.9 ≦ n (Li) ]/[ n (Ni) + n (Co) + n (M) ] ≦ 1.3; the additive N1 is used in an amount, calculated as N (G), such that 0 ≦ N (G) ]/[ N (Ni) + N (Co) + N (M) ] < 0.05, the M being selected from Al and/or Mn elements.

Further, the multinary material is calculated by [ n (Ni) + n (Co) + n (M) ], the first lithium source is calculated by n (Li), and the first lithium source is used in an amount of 0.95 ≦ n (Li) ]/[ n (Ni) + n (Co) + n (M) ] ≦ 1.2; the additive N1 is used in an amount of 0.01 to [ N (G) ]/[ N (Ni) + N (Co) + N (M) ] < 0.03, calculated as N (G).

According to the invention, in step (2), the first calcined material is used in an amount of 0. Ltoreq. N (R) ]/[ N (Ni) + N (Co) + N (M) ] < 0.05, more preferably 0.01. Ltoreq. N (R) ]/[ N (Ni) + N (Co) + N (M) ] < 0.03, in terms of N (R) ].

In the invention, the lithium iron manganese phosphate material precursor comprises Mn, fe and D elements, wherein D is at least one element selected from Mg, co, ni, cu, zn and Ti.

According to the invention, in the step (3), the lithium iron manganese phosphate material precursor and the second lithium source are used in an amount of 0.9 < [ n (Li) ]/[ n (Mn) + n (Fe) + n (D) ] < 1.2; the additive L1 is used in an amount of 0 < [ n (D') ]/[ n (Mn) + n (Fe) + n (D) ] < 0.04.

Further, the amount of the second lithium source used in the lithium iron manganese phosphate material precursor is 1 < [ n (Li) ]/[ n (Mn) + n (Fe) + n (D) ] < 1.1; the additive L1 is used in an amount of 0.01. Ltoreq. N (D')/[ n (Mn) + n (Fe) + n (D) ]. Ltoreq.0.03.

Further, in the step (3), the weight ratio of the lithium iron manganese phosphate material precursor to the first carbon source is 1:0.05 to 0.12, preferably 1:0.06-0.1.

According to the invention, in step (1), the conditions of the first calcination comprise: in an oxygen-containing atmosphere, the calcination temperature is 650-900 ℃, preferably 700-850 ℃, the calcination time is 6-30h, preferably 8-25h, and the oxygen concentration in the oxygen-containing atmosphere is more than or equal to 4vol%, preferably more than or equal to 8vol%.

In the present invention, the first calcination under the above-described conditions can produce a lithium iron manganese phosphate positive electrode material.

In the present invention, the kind of oxygen-containing atmosphere is not particularly limited, and may be an atmosphere having an oxygen concentration of not less than 4vol% which is conventional in the art.

According to the present invention, in the step (2), the conditions of the first heat treatment include: under the oxygen-containing atmosphere, the heat treatment temperature is 300-480 ℃, preferably 320-460 ℃, the heat treatment time is 5-15h, preferably 6-12h, and the oxygen concentration in the oxygen-containing atmosphere is more than or equal to 4vol%, preferably more than or equal to 8vol%.

In the preparation method, in the preparation process of the multi-component material, the first calcined material is coated by an optional additive N2, the first heat treatment is carried out on the coated first calcined material, particularly, the first heat treatment is carried out under the specific conditions, so that the lithium iron manganese phosphate material can only react with residual alkali on the surface of the multi-component material and cannot further enter the crystal lattice, an internal crystal structure for blocking shuttle of lithium ions cannot be formed, a thin coating layer is only formed on the surface of the multi-component material, and the cycle performance is effectively improved under the condition of not reducing the capacity of the material.

In the present invention, the drying conditions in step (3) are not particularly limited, and drying conditions conventional in the art may be employed, and include, for example: drying in a vacuum oven at 60-100 deg.C for 2-6 hr, preferably at 65-85 deg.C for 3-5 hr.

According to the invention, in step (3), the conditions of the second calcination include: under the protective atmosphere, the calcining temperature is 600-700 ℃, preferably 620-660 ℃, and the calcining time is 8-12 h, preferably 9-11 h.

In the invention, the second calcination is carried out under the specific conditions, which is beneficial to improving the reaction activity of the anode material, is beneficial to the close contact of the multi-component material and the lithium iron manganese phosphate material, optimizes the particle size distribution of the secondary particles, and effectively improves the rate capability and the cycle performance. Performing the second heat treatment in an oxygen-containing atmosphere to prevent Ni from being generated during the heat treatment ³⁺ Is reduced to Ni ²⁺ And the cations migrate to the lithium position to be mixed and discharged, so that the performance of the material is influenced.

In the present invention, the kind of the protective atmosphere is not particularly limited, and may be a protective atmosphere that is conventional in the art, for example, at least one selected from nitrogen, argon, and helium.

Precursor of multicomponent material

In the present invention, the multi-component material precursor is not particularly limited, and can be prepared by a preparation method that is conventional in the art, for example, the multi-component material precursor is prepared by the following steps:

(A) Preparing a mixed salt solution from nickel salt, cobalt salt and an additive N3; respectively preparing a first precipitator and a first complexing agent into a first precipitator solution and a first complexing agent solution;

(B) Preparing phosphate into phosphate solution;

(C) And adding the mixed salt solution, the first precipitator solution, the phosphate solution and the first complexing agent into a reaction kettle, carrying out a first coprecipitation reaction, and aging, filtering, washing and drying to obtain the multi-component material precursor.

According to the invention, phosphate is introduced in situ at the precursor stage of the multi-component material, so that a unique phosphate phase is arranged in the phase in the preparation process, the phase can stabilize the layered structure of the matrix material, effectively prevent the collapse of the layered structure in a high-charge state and the transformation to other rock salt phases, delay the structural failure of the anode material, and greatly improve the safety performance.

In the present invention, the kind of the phosphate is not particularly limited, and may be a phosphate conventionally used in the art, for example, selected from monoammonium phosphate and/or diammonium phosphate.

In the present invention, in the step (B), the salt solution is mixed with the phosphate solution in terms of n (P) in such an amount that 0 < n (P)/[ n (Ni) + n (Co) + n (M) ]. Ltoreq.0.01, preferably 0 < n (P)/[ n (Ni) + n (Co) + n (M) ]. Ltoreq.0.007, in terms of [ n (Ni) + n (M) ]. Ltoreq.n (P) ].

In the invention, the concentration of the phosphate solution is 1-3mol/L, preferably 1.5-2.5mol/L.

In the present invention, the kind of the nickel salt is not particularly limited, and may be a nickel salt that is conventional in the art, for example, at least one of nickel sulfate, nickel chloride, nickel nitrate, and nickel acetate.

In the present invention, the kind of the cobalt salt is not particularly limited, and may be a cobalt salt that is conventional in the art, for example, at least one of cobalt sulfate, cobalt chloride, cobalt nitrate, and cobalt acetate.

According to the invention, the additive N3 is a compound containing an element M selected from the group consisting of Al and/or Mn elements.

Further, the kind of the compound containing the M element is not particularly limited, and may be at least one of an oxide, a carbonate, a fluoride, a boride, a hydroxide, a sulfate, a nitrate, and a chloride, and preferably at least one of a sulfate, a nitrate, and a chloride, for example.

According to the invention, the nickel salt, the cobalt salt and the additive N3 are mixed according to the formula Ni: co: m = (1-x-y-z-M): x: y is more than or equal to 0.5 and less than or equal to 1-x-y-z-m and less than or equal to 1,x and less than or equal to (1-x-y-z-m), y is more than or equal to 0 and less than or equal to 0.25,0 and less than or equal to z and less than or equal to 0.05,0 and less than or equal to m and less than 0.05.

Furthermore, e is more than or equal to 0.95 and less than or equal to 1.2,0.6 and less than or equal to 1-x-y-z-m and less than 0.9,0.05 and less than or equal to 0.2,0.01 and less than or equal to z and less than or equal to 0.03,0.01 and less than or equal to m and less than 0.03.

In the invention, the total concentration of nickel salt, cobalt salt and additive N3 in the mixed salt solution is 1-3mol/L.

In the invention, the additive N3 is beneficial to the rapid diffusion of molecules, so that the solution is uniformly mixed.

In the present invention, the kind of the first precipitant is not particularly limited, and may be a precipitant conventional in the art, for example, at least one selected from ammonium carbonate, ammonium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium hydroxide, potassium hydroxide, and lithium hydroxide.

In the present invention, the concentration of the first precipitant solution is 2 to 8mol/L, preferably 4 to 6mol/L.

In the present invention, the kind of the first complexing agent is not particularly limited, and may be a complexing agent that is conventional in the art, for example, at least one selected from the group consisting of ammonia water, disodium ethylenediaminetetraacetate, ammonium nitrate, triammonium citrate, ammonium chloride, and ammonium sulfate.

In the invention, the concentration of the first complexing agent solution is 2-4mol/L, preferably 2.5-3.5mol/L.

According to the invention, in step (C), the first coprecipitation reaction conditions comprise: under protective atmosphere, the reaction temperature is 40-70 deg.C, preferably 50-60 deg.C, and the pH value is kept at 11-13, preferably 11.5-12.5 during the reaction.

According to the invention, the aging time is between 2h and 12h, preferably between 6 and 10h.

In the invention, the aged multi-component material precursor is washed by pure water and/or alkaline solution, the type and concentration of the alkaline solution are not particularly limited, and the alkaline solution which is conventional in the art can be used.

Precursor of lithium iron manganese phosphate material

According to the invention, the lithium manganese iron phosphate material precursor is prepared according to the following steps:

(a) Preparing manganese salt, ferric salt and an additive L2 into a first mixed solution; preparing a phosphorus source and an ammonia source into a second mixed solution; preparing a first suspension from a second complexing agent and a second carbon source;

(b) Adding the first mixed solution and the second mixed solution into the first suspension for a second coprecipitation reaction to obtain a second coprecipitation slurry;

(c) And carrying out solid-liquid separation and washing on the second coprecipitation slurry to obtain a lithium iron manganese phosphate material precursor.

In the invention, the second carbon source is introduced in the preparation process of the precursor, can be uniformly coated on the surface of the primary particles to form a stable conductive network, and enables the primary particles to be tightly bonded and agglomerated to form compact secondary spherical particles.

In the present invention, the kind of the manganese salt is not particularly limited, and may be a manganese salt that is conventional in the art, for example, at least one of manganese sulfate, manganese chloride, manganese nitrate, and manganese acetate.

In the present invention, the kind of the iron salt is not particularly limited, and may be an iron salt that is conventional in the art, for example, at least one of iron sulfate, ferrous sulfate, iron nitrate, iron acetate, and iron chloride.

According to the invention, the additive L2 is a compound containing a doping element D selected from at least one of Mg, co, ni, cu, zn and Ti.

Further, the doping element D is at least one element selected from Mg, cu, and Ti.

In the present invention, the kind of the compound containing the doping element D is not particularly limited, and may be at least one of an oxide, a carbonate, a fluoride, a boride, a hydroxide, a sulfate, a nitrate, and a chloride, and preferably at least one of a sulfate, a nitrate, and a chloride.

According to the invention, the molar ratio of the manganese salt, the iron salt and the additive L2 in the first mixed solution is Mn: fe: d = (1-h-k-j): h: k is more than 0.1 and less than or equal to 0.4,0 and more than or equal to 0.04,0 and more than or equal to j and less than or equal to 0.04.

Furthermore, h is more than 0.15 and less than or equal to 0.35,0.01 and less than or equal to k is less than or equal to 0.03,0.01 and less than or equal to j is less than or equal to 0.03.

In the present invention, the kind of the phosphorus source is not particularly limited, and may be a phosphate ion-containing compound that is conventional in the art, for example, at least one of phosphoric acid, monoammonium phosphate, and triammonium phosphate.

In the present invention, the kind of the ammonia source is not particularly limited, and may be a compound containing ammonium ions, which is conventional in the art, such as at least one of ammonia water, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, triammonium phosphate, ammonium hydrogen carbonate, ammonium sulfate, and urea, and preferably at least one of ammonia water, ammonium monohydrogen phosphate, and ammonium dihydrogen phosphate.

In the invention, the dosage of the phosphorus source and the ammonia source meets the following requirements: the molar ratio of the phosphorus source calculated by phosphate ions to the ammonia source calculated by ammonium ions is 1:1-3.

In the present invention, the phosphorus source and the ammonia source may be the same compound, and when a compound containing phosphorus and ammonia is used as both the phosphorus source and the ammonia source, the molar ratio of phosphorus to ammonia in the compound is such that the molar ratio of the phosphorus source to the ammonia source is 1:1-3.

According to the invention, the second carbon source is selected from at least one of graphene, carbon nanotubes, phenolic resin, polyethylene, polyvinylidene fluoride, polytetrafluoroethylene, polypropylene and toluene diisocyanate.

In the present invention, the kind of the second complexing agent is not particularly limited, and may be a complexing agent that is conventional in the art, for example, at least one selected from the group consisting of ammonia water, disodium ethylenediaminetetraacetate, ammonium nitrate, triammonium citrate, ammonium chloride, and ammonium sulfate. The first complexing agent and the second complexing agent may be the same or different in kind.

In the invention, the concentration of the second complexing agent solution in the first suspension is 0.01-2mol/L, and preferably 0.02-1.5mol/L.

According to the invention, the weight ratio of the second complexing agent to the second carbon source is 1:1-5, preferably 1:2-4.

In the present invention, the second coprecipitation reaction condition includes: under protective atmosphere, the reaction temperature is 40-70 deg.C, preferably 45-65 deg.C, and the pH value is kept at 5-7, preferably 5.5-6.5 during the reaction.

The invention also provides a composite cathode material prepared by the preparation method.

When the composite cathode material is used for a lithium ion battery, the composite cathode material has good structural stability in the charging and discharging processes, the specific discharge capacity exceeds a theoretical value, and the cycle performance is excellent. The safety performance of the battery is ensured while high charge and discharge capacity is ensured.

According to the invention, the coated lithium iron manganese phosphate material with a stable structure delays the thermal decomposition temperature of the composite anode material, reduces the heat released by thermal runaway, improves the safety of the battery, and prolongs the cycle life of the lithium ion battery.

According to a particularly preferred embodiment of the present invention, the composite cathode material has a full width at half maximum FWHM of a (110) crystal plane obtained by XRD measurement ₍₁₁₀₎ And FWHM of full width at half maximum of (111) crystal plane ₍₁₁₁₎ The following conditions are satisfied:

0.2≤FWHM ₍₁₁₀₎ ≤0.24，0.22≤FWHM ₍₁₁₁₎ ≤0.25；

0.7≤FWHM ₍₁₁₀₎ /FWHM ₍₁₁₁₎ ≤1。

the present invention will be described in detail below by way of examples. In the following examples and comparative examples, the starting materials used were all commercially available products.

The preparation processes of the composite positive electrode materials (S1 to S12 and T1 to T8) prepared in examples 1 to 12 and comparative examples 1 to 8 are shown in table 1 to 2, wherein the chemical compositions and the compounding ratios of the multi-component material and the lithium iron manganese phosphate material are shown in table 3. Physical property parameters of the composite positive electrode materials (S1-S12 and T1-T8) obtained in examples 1-12 and comparative examples 1-8 are shown in tables 4-6.

Preparation example A1

Preparation of multi-element anode material precursor

(A) Adding nickel sulfate, cobalt sulfate and manganese sulfate into water together according to a molar ratio of 60. 10mol/L ammonia water solution is prepared to be used as a first complexing agent solution, and 4mol/L sodium hydroxide solution is prepared to be used as a first precipitator solution.

(B) Preparing ammonium dihydrogen phosphate into 2mol/L phosphate solution with n (P)/[ n (Ni) + n (Co) + n (M) ] = 0.002;

(C) Introducing nitrogen into the reaction kettle for a certain time to ensure that no air atmosphere exists in the kettle, adding the mixed salt solution, the first precipitator solution, the phosphate solution and the first complexing agent solution into the reaction kettle to perform a first coprecipitation reaction, controlling the stirring speed to be 500rpm, adjusting the pH value to be 11.8, controlling the temperature of the reaction kettle to be 60 ℃, aging the materials after the reaction is completed, wherein the aging time is 8h, and alternately washing alkaline solution and pure water at 75 ℃. And drying and sieving the filter cake to obtain the multi-component material precursor A1.

Preparation A2

The multi-component precursor A2 was prepared according to the method of preparation A1, except that: in the step (A), nickel sulfate, cobalt sulfate and manganese sulfate are added into water together according to the molar ratio of 70. And preparing the obtained multi-component material precursor A2.

Preparation example A3

A multi-component material precursor A3 was prepared according to the method of preparation A1, except that: in the step (A), nickel sulfate, cobalt sulfate and manganese sulfate are added into water together according to the molar ratio of 80. And preparing the obtained multi-component material precursor A3.

Preparation example A4

A multi-component precursor A4 was prepared according to the method of preparation A1, except that: the phosphate solution preparation in step (B) was not carried out. And preparing the obtained multi-component material precursor A4.

Preparation example A5

A multi-component precursor A5 was prepared according to the method of preparation A2, except that: the phosphate solution preparation in step (B) was not carried out. And preparing the obtained multi-component material precursor A5.

Preparation example A6

A multi-component precursor A6 was prepared according to the method of preparation A3, except that: the phosphate solution preparation in step (B) was not carried out. And preparing the obtained multi-element material precursor A6.

Preparation B1

Preparation of lithium iron manganese phosphate material precursor

(a) Manganese sulfate, ferric sulfate and magnesium sulfate are mixed according to a molar ratio of 60:39:1, preparing 2L of first mixed solution with the total metal ion concentration of 2 mol/L; phosphoric acid and ammonia water are mixed according to the formula of n (PO) ₄ ⁺ ):n(NH ₃ ⁺ ) =1:3, 4L of second mixed solution with phosphate radical ion concentration of 1mol/L is prepared; mixing triammonium citrate and polyvinylidene fluoride according to a mass ratio of 1:3, preparing 1L of first suspension, wherein the concentration of a second complexing agent in the first suspension is 0.05mol/L;

(b) Adding the first suspension as a reaction base solution into a reaction kettle, dropwise adding the first mixed solution and the second mixed solution into the reaction kettle, controlling the pH value in the reaction system to be 5.5-6.5, controlling the temperature to be 60 ℃, stirring at the speed of 800rpm, and after the feeding is finished, continuously stirring for 1h to obtain second coprecipitation slurry;

(c) And carrying out suction filtration and washing on the second coprecipitation slurry until the conductivity of the filtrate is less than or equal to 200 mu s/cm, thus obtaining a lithium iron manganese phosphate material precursor B1.

Example 1

(1) The precursor A1 of the multielement material is mixed with lithium hydroxide according to the mol ratio n (Li)]/[n(Ni)+n(Co)+n(M)]Is 1:1.03, and then Nb is added ₂ O ₅ Dry mixing is continued as additive N1 with the premix, and the premix and additive N1 are used in an amount of N (Nb)/[ N (Ni) + N (Co) + N (M) in terms of the molar ratio of the multi-component material precursor A1 to Nb]=0.003, and calcining the mixture at 765 ℃ for 20h in an oxygen atmosphere with an oxygen concentration of 8vol%.

(2) Using Y to the first calcined material ₂ O ₃ As additive N2, the first calcined material is coated with [ N (Ni) + N(Co)+n(M)]In terms of N (Y), N (Y)/[ N (Ni) + N (Co) + N (M) for the additive N2]And =0.001, the above materials were mixed by a dry method. And carrying out first heat treatment, controlling the heat treatment temperature at 350 ℃, carrying out heat treatment for 12 hours in an oxygen-containing atmosphere with the oxygen concentration of 8vol%, and then cooling and sieving a first heat treatment product to obtain the multi-element material.

(3) Taking a lithium iron manganese phosphate material precursor B1, lithium carbonate and titanium dioxide according to a molar ratio of 1:0.52:0.01, mixing a manganese lithium iron phosphate material precursor B1 and glucose according to a mass ratio of 1:0.08, mixing with pure water, homogenizing, evaporating to dryness, drying in a vacuum oven at 85 ℃ for 4 hours to obtain a dry material, calcining the dry material at 650 ℃ for 10 hours in a nitrogen atmosphere, and screening to obtain the lithium iron manganese phosphate anode material.

(4) And simultaneously putting the multielement material and the lithium iron manganese phosphate material into a high-speed mixer according to the mass ratio of 8:2, mixing for 4 hours at the rotating speed of 400rpm, carrying out second heat treatment for 3 hours in a muffle furnace under the oxygen-containing atmosphere with the oxygen concentration of 8vol% at 200 ℃, then discharging and sieving to obtain the composite anode material marked as S1.

Example 2

A composite positive electrode material was prepared according to the method of example 1, except that:

(4) The multielement material and the lithium manganese iron phosphate material are prepared according to the following steps of 9:1, performing second heat treatment in a muffle furnace at 200 ℃ in an oxygen-containing atmosphere with the oxygen concentration of 8vol% for 3h, discharging and sieving to obtain a composite cathode material, and recording as S2.

Example 3

and (4) mixing the multielement material and the lithium iron manganese phosphate material according to the mass ratio of 7:3, performing secondary heat treatment in a muffle furnace at 200 ℃ for 3 hours in an oxygen-containing atmosphere with the oxygen concentration of 8vol%, discharging and sieving to obtain the composite anode material, wherein the composite anode material is marked as S3.

Example 4

in the step (4), the multi-element material and the lithium iron manganese phosphate material are mixed according to the mass ratio of 6:4, and are subjected to secondary heat treatment in a muffle furnace for 3 hours at 200 ℃ in an oxygen-containing atmosphere with the oxygen concentration of 8vol%, then the material is discharged and sieved, and the composite anode material is obtained and is marked as S4.

Example 5

in the step (4), the multi-element material and the lithium iron manganese phosphate material are mixed according to the mass ratio of 5:5, and are subjected to secondary heat treatment in a muffle furnace for 3 hours at 200 ℃ in an oxygen-containing atmosphere with the oxygen concentration of 8vol%, then the material is discharged and sieved, and the composite anode material is obtained and is marked as S5.

Example 6

(1) Mixing a multi-component material precursor A2 and lithium hydroxide according to a molar ratio of 1: dry premixing was carried out at a ratio of 1.03.

And preparing to obtain the composite cathode material, and recording as S6.

Example 7

(1) Mixing a multi-component material precursor A3 and lithium hydroxide according to a molar ratio of 1: dry premixing was carried out at a ratio of 1.03.

A composite positive electrode material was obtained, denoted as S7.

Example 8

(1) And (3) mixing a multi-component material precursor A4: lithium hydroxide is added according to a molar ratio of 1: dry premixing was carried out at a ratio of 1.03.

And obtaining the composite cathode material after the preparation is finished, and marking as S8.

Example 9

(1) And (3) mixing a multi-component material precursor A5: lithium hydroxide is added according to a molar ratio of 1: dry premixing was carried out at a ratio of 1.03.

And obtaining the composite cathode material after the preparation is finished, and marking as S9.

Example 10

(1) And (3) mixing a multi-component material precursor A6: lithium hydroxide is added according to a molar ratio of 1: dry premixing was carried out at a ratio of 1.03.

And obtaining the composite cathode material after the preparation is finished, and marking as S10.

Example 11

(4) And mixing the multielement material and the lithium iron manganese phosphate material according to the mass ratio of 8:2, carrying out second heat treatment for 3h at 120 ℃ in a muffle furnace in an oxygen-containing atmosphere with the oxygen concentration of 8vol%, discharging and sieving to obtain the composite anode material, and recording as S11.

Example 12

(4) And mixing the multielement material and the lithium iron manganese phosphate material according to the mass ratio of 8:2, carrying out second heat treatment in a muffle furnace at 350 ℃ in an oxygen-containing atmosphere with the oxygen concentration of 8vol% for 3h, discharging and sieving to obtain the composite anode material, and marking as S12.

TABLE 1

TABLE 1 (continuation)

Comparative example 1

the preparation process of the steps (3) to (4) is not carried out, and the multielement material is obtained and is marked as T1.

Comparative example 2

(1) Mixing a multi-element material precursor A2 and lithium hydroxide according to a molar ratio of 1: dry premixing was carried out at a ratio of 1.03.

The preparation process of the steps (3) to (4) is not carried out, and the multielement material is obtained and is marked as T2.

Comparative example 3

The preparation process of the steps (3) to (4) is not carried out, and the multielement material is obtained and is marked as T3.

Comparative example 4

and (4) not carrying out the preparation processes of the steps (1) - (2) and (4), and obtaining the lithium iron manganese phosphate material which is marked as T4.

Comparative example 5

(4) Without the second heat treatment, a composite positive electrode material was obtained, denoted as T5.

Comparative example 6

(1) Mixing a multi-component material precursor A4 and lithium hydroxide according to a molar ratio of 1:1.03, and directly carrying out primary calcination without doping elements.

(2) Directly carrying out first heat treatment on the first calcined material without doping elements, controlling the heat treatment temperature at 350 ℃, and carrying out heat treatment for 12 hours in an oxygen-containing atmosphere with the oxygen concentration of 8vol%, and then cooling and sieving a first heat treatment product to obtain the multi-element material.

(4) Without the second heat treatment, a composite positive electrode material was obtained, denoted as T6.

Comparative example 7

(4) And carrying out second heat treatment for 3h at 200 ℃ in a muffle furnace under the nitrogen atmosphere to obtain the composite cathode material, which is marked as T7.

Comparative example 8

(4) And mixing the multielement material and the lithium iron manganese phosphate material according to the mass ratio of 8:2, carrying out second heat treatment for 3h at 500 ℃ in a muffle furnace in an oxygen-containing atmosphere with the oxygen concentration of 8vol%, discharging and sieving to obtain the composite anode material, and marking as T8.

TABLE 2

Table 2 (continuation)

TABLE 3

Test example 1

The particle size of the composite anode material is obtained by adopting a laser particle size analyzer MASTERSIZER2000 test;

an XRD test was performed on 2g of the composite positive electrode material obtained in the example and comparative example, using an X-ray diffractometer (λ =0.15406 nm) manufactured by Rigaku corporation of Japan under the test conditions of an operating voltage of 40kV, an operating current of 250mA, a scanning speed of 4 °/min, a step size of 0.02 °, and a scanning range of 2 θ of 10 ° -80 °.

The micro-morphology of the composite cathode material is obtained by a scanning electron microscope test, and the used instrument is an S-4800 type scanning electron microscope of Hitachi corporation in Japan.

Crystal grain diameter of composite positive electrode material, full width at half maximum FWHM of (110) crystal plane ₍₁₁₀₎ And FWHM of full width at half maximum of (111) crystal plane ₍₁₁₁₎ The results are shown in Table 4.

TABLE 4

Note: the results of the tests for the half-peak widths of the (110) and (111) crystal planes of the composite positive electrode material were partially missing because the half-peak widths of the (110) and (111) crystal planes were not measured.

The average particle size of the composite cathode material prepared in examples 1 to 12 is within the range of 2 to 10 μm, a lithium manganese iron phosphate material is uniformly attached to the surface of the multi-component material, and the lithium manganese iron phosphate material is enriched and agglomerated on the surface of the multi-component material, and the multi-component material is embedded therein, so that the particles of the composite cathode material are arranged more tightly.

Fig. 1 is a scanning electron microscope image of 10K times of the composite cathode material prepared in comparative example 1, the comparative example 1 is a multielement material which is not coated with a lithium manganese iron phosphate material, in the image, it can be observed that the microscopic morphology of the multielement material prepared in comparative example 1 is spheroidal particles, fig. 2 is a scanning electron microscope pattern of 10K times of the composite cathode material prepared in comparative example 4, the comparative example 4 is a lithium manganese iron phosphate material of a coating layer, the particle size of the lithium manganese iron phosphate material is uniform, the primary particle size is in a submicron level, and the particle size is 500nm.

Fig. 3, 4, and 5 are scanning electron micrographs of the composite positive electrode materials T5, T7, and T8 prepared in comparative example 5, comparative example 7, and comparative example 8, respectively, magnified by 10.0K times, and it can be observed that the lithium iron manganese phosphate particles on the surfaces of the composite positive electrode material particles prepared in T5, T7, and T8 are not uniformly attached to the multi-component material particles, and are loose from particle to particle. The second heat treatment is carried out in an oxygen-containing atmosphere at the temperature of 100-400 ℃, so that the lithium iron manganese phosphate material can be uniformly coated on the surface of the multi-component material, and the particles of the composite anode material are more closely arranged.

Fig. 6 is a scanning electron microscope pattern obtained by amplifying the composite cathode material obtained in example 1 by 10K times, and it can be seen from fig. 6 that the lithium manganese iron phosphate material is uniformly attached to the surface of the multi-component material of the composite cathode material obtained in example 1, and the lithium manganese iron phosphate material is enriched and agglomerated on the surface of the multi-component material, and the multi-component material is embedded therein, so that the particles of the composite cathode material are arranged more tightly.

As can be seen from Table 4, examples 1 to 12 of the present invention provide composite positive electrode materials having FWHM of full width at half maximum of (110) crystal plane, relative to comparative examples 1 to 8 ₍₁₁₀₎ Satisfy FWHM of 0.18 ≤ and ₍₁₁₀₎ less than or equal to 0.25, FWHM of full width at half maximum of (111) crystal face ₍₁₁₁₎ Satisfy FWHM of 0.2-0 ₍₁₁₁₎ ≤0.26。

Further, examples 1 to 12 of the present invention provide composite positive electrode materials having a full width at half maximum FWHM of a (110) crystal plane ₍₁₁₀₎ And FWHM of full width at half maximum of (111) crystal plane ₍₁₁₁₎ The ratio of (A) satisfies the FWHM of 0.6-15 ₍₁₁₀₎ /FWHM ₍₁₁₁₎ ≤1.1。

Fig. 7 is an X-ray diffraction analysis pattern of the composite positive electrode materials prepared in comparative example 1, comparative example 4, and example 1. The comparative example 1 is a multi-component material which is not coated with a lithium iron manganese phosphate material, and as can be seen from fig. 7, no other impure-phase peak is present in the XRD spectrum of the comparative example 1 except for the main-phase characteristic peak of the multi-component material, the two pairs of characteristic peaks (006)/(012) and (018)/(110) are split clearly, and the strength ratio of (003) to (104) is greater than 1.2, which indicates that the multi-component material per se has good crystallization and a good layered structure. And the comparative example 4 is an XRD (X-ray diffraction) pattern of a pure lithium manganese iron phosphate material, and no impurity peak is generated in the XRD pattern except a main phase characteristic diffraction peak. The XRD spectrogram of the composite cathode material S1 prepared in example 1 shows characteristic diffraction peaks of the multi-component material and lithium manganese iron phosphate, and the positions of the peaks do not shift, which indicates that the crystal structures of the two materials are not changed in the mechanical mixing process and the second heat treatment process of the present invention.

The XRD test results of examples 1-12 show that the lithium iron manganese phosphate material as a coating layer in the composite positive electrode material provided by the present invention does not enter the lattice interior of the multi-component material, thereby ensuring that the structure of the multi-component material is not changed, and improving the stability and safety of the composite positive electrode material in the cycle process without affecting the capacity of the multi-component material.

Fig. 7 is an XRD pattern of the composite positive electrode material prepared in comparative example 5 without the second heat treatment, which shows characteristic diffraction peaks of the multi-component material and the lithium iron manganese phosphate material, and the positions of the peaks do not shift. However, comparative example 5 provides a composite positive electrode material having a full width at half maximum FWHM of the (110) crystal plane ₍₁₁₀₎ FWHM of (111) crystal plane at half maximum width =0.178 ₍₁₁₁₎ =0.262, not within the specific range defined in the present invention.

By adopting the specific second heat treatment conditions of the invention, the composite cathode materials prepared in the comparative example 1 and the comparative example 5, and the comparative example 7 and the comparative example 8 can be tightly combined, and small particles are uniformly attached to the surface of large particles, so that the composite cathode material comprising the multi-component material and the lithium iron manganese phosphate material has proper crystallinity and good structural stability.

Application example 1

The lithium ion battery is assembled by the composite cathode materials prepared in the embodiments and the comparative examples, and the assembling process is specifically as follows:

the CR2025 button cell was prepared as follows:

fully compounding the prepared composite cathode material sample with conductive carbon black, polyvinylidene fluoride and lithium bis (trifluoromethanesulfonyl) imide according to a mass ratio of 90 ² . The lithium metal sheet is taken as a negative electrode, the polypropylene microporous membrane is taken as a diaphragm and contains 1mol/LLIPF ₆ The electrolyte solution of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate is assembled into a CR2025 button cell in a glove box filled with argon.

The charge-discharge cycle performance of the lithium ion battery assembled by the composite anode material is tested by adopting a CR2025 button cell, the used instrument is a Xinwei battery test system, the test conditions are that the charge-discharge test is carried out at 25 ℃ and 3-4.3V, and the charge-discharge cycle performance test is carried out for 80 times of charge-discharge, and the results are shown in Table 5.

TABLE 5

Fig. 8 is a charge-discharge curve of the lithium ion battery assembled by the composite cathode materials prepared in comparative example 1, comparative example 4 and example 1 at 0.1C, and it can be seen from fig. 8 that, compared to comparative example 1 and comparative example 4, the lithium ion battery assembled by the composite cathode material provided in inventive example 1 exhibits higher first charge-discharge efficiency, because the coated carbon of the submicron-sized lithium manganese iron phosphate material in the composite cathode material inhibits the growth of particles and reduces the diffusion distance of lithium ions, and on the other hand, can enhance the overall conductivity of the material, provides a convenient electron transport path, facilitates charge transport and lithium ion diffusion, facilitates the exertion of the capacity of the multi-component material, and thus improves the electrochemical performance of the composite cathode material.

Fig. 9 is a cycle performance graph of lithium ion batteries assembled by the composite cathode materials prepared in comparative example 1, comparative example 4 and example 1 at 0.1C, and it can be seen from fig. 9 that the specific discharge capacities of the lithium ion batteries assembled by the composite cathode materials prepared in comparative example 1, example 1 and comparative example 4 after 80 weeks of cycle are 160.2mAh/g,158.2mAh/g and 136.6mAh/g, and the capacity retention rates are 94.9%, 95.7% and 97.4%, respectively.

The multi-element material sample prepared in the comparative example 1 has good crystallinity, few internal defects, small specific surface area, good compatibility with electrolyte and good circulation stability; the lithium iron manganese phosphate material prepared in the comparative example 4 has PO formed by stronger P-O bonds ₄ The tetrahedron can effectively stabilize an oxygen framework in a crystal structure, reduces oxygen release side reaction, and has excellent cycle performance.

The composite positive electrode material prepared in example 1 exhibited superior capacity retention rate than the multi-component material. When the composite positive electrode material is mainly made of a multi-element material, the surface of the surrounding lithium iron manganese phosphate material is coated with carbon to reinforce the electronic conductivity of the conductive carbon black in the positive plate, so that the polarization of the battery is reduced, and the redox reversibility is improved; the lithium iron manganese phosphate material can prevent direct contact between the multi-component material and the organic electrolyte, reduce the probability of side reaction between the multi-component material and the organic electrolyte, and enhance the stability of the composite anode material in the circulation process.

As can be seen from the results of table 5, comparative example 5 employs the same preparation method as example 1 except that the second heat treatment is not performed, and compared to example 1, the first specific discharge capacity, the first coulombic efficiency, the specific discharge capacity after 80 cycles, and the capacity retention rate of the lithium ion battery assembled from the composite cathode material prepared in comparative example 5 are lower than those of example 1.

Further, comparative example 7 and comparative example 8 employed the same preparation method as example 1 except that comparative example 7 performed the second heat treatment in an oxygen-free atmosphere and comparative example 8 raised the second heat treatment temperature to 500 ℃. Compared with the embodiment 1, the lithium ion battery assembled by the composite cathode materials prepared in the comparative example 7 and the embodiment 8 has lower first discharge specific capacity, first coulombic efficiency, specific discharge capacity after 80 weeks of circulation and capacity retention rate than the embodiment 1.

The invention is shown that the multi-component material and the lithium iron manganese phosphate material are mixed by the second heat treatment in the oxygen-containing atmosphere at the temperature of 100-400 ℃, and the cycle performance is effectively improved under the condition of not reducing the capacity of the multi-component material.

Further, example 8 has the same Ni: co: m molar ratio and the same multielement material: the blending ratio of the lithium iron manganese phosphate material is different from that of the material without adding phosphate radical. Compared with example 1, the specific first discharge capacity, the first coulombic efficiency, the specific discharge capacity after 80 weeks of cycling and the capacity retention rate of example 8 are all lower than those of example 1. The introduction of phosphate radical in the preparation of the precursor is helpful for improving the electrochemical performance of the composite cathode material.

Example 1, example 6 and example 7 each used different Ni: co: the molar ratio of M is used for preparing the composite cathode material, the content of the Ni element added in the composite cathode materials prepared in the embodiments 6 and 7 is higher than that in the embodiment 1, the first discharge specific capacity of the lithium ion battery assembled by the composite cathode materials prepared in the embodiments 6 and 7 is higher than that in the embodiment 1, and the first coulombic efficiency, the discharge specific capacity after 80 weeks of circulation and the capacity retention rate are lower than those in the embodiment 1. The increase of the Ni element content can improve the first discharge specific capacity of the lithium ion battery assembled by the composite anode material, but can weaken the electrochemical stability.

Application example 2

The composite cathode materials prepared in the examples and comparative examples were assembled into lithium ion batteries for thermal stability testing, and the thermal stability of the composite cathode materials was evaluated by differential thermal-thermogravimetric tester test using a Mettler Toledo thermal analyzer (sweden).

The same method as application example 1 was used to prepare a CR2025 button cell under the test conditions that the CR2025 button cell was charged and discharged 2 times at 3-4.3V, 0.2C, 25 ℃ and then charged to a full charge state and disassembled to obtain a positive plate, and then the positive plate was placed in a differential thermal-thermogravimetric tester to be tested to obtain a DSC curve corresponding to the sample, with the test results shown in table 6.

TABLE 6

As can be seen from the results of table 6, the composite positive electrode materials provided by examples 1 to 12 of the present invention have smaller heat release and better thermal stability than those of comparative examples 1 to 8. The manganese lithium iron phosphate material with stable structure delays the occurrence of the thermal decomposition temperature of the multielement material, reduces the heat released by thermal runaway, and improves the safety of the battery.

Comparative example 5 the same preparation method as in example 1 was used, except that the second heat treatment was not performed, and the positive electrode sheet of the composite positive electrode material obtained in comparative example 5 exhibited a larger heat release amount and an earlier onset and peak heat release temperatures in the DSC test results than in example 1, indicating that the multi-component material and the lithium iron manganese phosphate material could not be sufficiently combined only by mechanical mixing and that there was still a problem of poor thermal stability.

Further, comparative example 7 was subjected to the second heat treatment in an oxygen-free atmosphere, comparative example 8 was subjected to the second heat treatment at a temperature raised to 500 ℃, and DSC tests showed that the positive electrode sheets of the composite positive electrode materials prepared in comparative example 7 and comparative example 8 exhibited a larger heat release amount, an earlier heat release start temperature and peak heat release temperature, and poor thermal stability as compared to example 1. The thermal stability of the composite material can be effectively improved through the heat treatment under specific conditions.

Further, example 8 has the same Ni: co: m molar ratio and the same multielement material: the lithium iron manganese phosphate material blend ratio, which is different from that in which no phosphate was added, was greater in the heat release amount of the positive electrode sheet of the composite positive electrode material obtained in example 8 in the DSC test and the onset heat release temperature and peak heat release temperature appeared earlier than in example 1. The addition of phosphate to the multi-component material also contributes to the improvement of the thermal stability of the composite positive electrode material.

The blending ratio of the multi-component material and the lithium manganese iron phosphate material in the composite cathode material prepared in the embodiment 2 is 9:1, the compounding ratio of the composite cathode material in the embodiment 1 is 8:2, and the lithium manganese iron phosphate material coated in the embodiment 1 is more than that in the embodiment 2, so that the heat release amount of the prepared composite cathode material in a thermal stability test is smaller, the thermal stability is improved, and the heat release amount of the prepared composite cathode material is reduced and the thermal stability is better along with the increase of the addition amount of the lithium manganese iron phosphate material.

Fig. 10 is a differential scanning calorimetry graph of the positive electrode sheets of the composite positive electrode materials obtained in example 1 and comparative example 1, and it can be seen from fig. 10 that the maximum heat flux value and the total heat release of the composite positive electrode material obtained in example 1 are much smaller than those of comparative example 1, and the initial heat release temperature and the maximum heat flux value temperature also appear later. The composite cathode material prepared in the embodiment 1 shows better thermal stability than a multi-element material, and the heat release of the composite material is reduced and the overall thermal stability of the material is improved due to the compounding of the lithium iron manganese phosphate material with a stable structure.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims

1. The composite positive electrode material is characterized by comprising a multi-element material and a lithium manganese iron phosphate material;

the composite anode material is tested by XRDFWHM of full width at half maximum of the obtained (110) crystal plane ₍₁₁₀₎ And FWHM of full width at half maximum of (111) crystal plane ₍₁₁₁₎ The following conditions are satisfied:

0.18≤FWHM ₍₁₁₀₎ ≤0.25，0.2≤FWHM ₍₁₁₁₎ ≤0.26；

preferably, 0.2 ≦ FWHM ₍₁₁₀₎ ≤0.24，0.22≤FWHM ₍₁₁₁₎ ≤0.25。

2. The composite positive electrode material according to claim 1, wherein the composite positive electrode material has a full width at half maximum (FWHM) of a (110) crystal plane obtained by XRD testing ₍₁₁₀₎ And FWHM of full width at half maximum of (111) crystal plane ₍₁₁₁₎ The following conditions are satisfied:

0.6≤FWHM ₍₁₁₀₎ /FWHM ₍₁₁₁₎ ≤1.1；

preferably, 0.7 ≦ FWHM ₍₁₁₀₎ /FWHM ₍₁₁₁₎ ≤1。

3. The composite positive electrode material according to claim 1 or 2, wherein the multi-component material has a composition represented by formula I:

Li _e (Ni _1-x-y-z-m Co _x M _y G _z R _m )O _q (PO ₄ ) _n formula I;

wherein e is more than or equal to 0.9 and less than or equal to 1.3, x is more than or equal to (1-x-y-z-m), y is more than or equal to (1-x-y-z-m), 0.5 is more than or equal to 1-x-y-z-m and is more than 1,0 and is more than or equal to 0.25,0 and is more than or equal to z and is more than 0.05,0 and is more than or equal to m and is more than 0.05,0 and is more than or equal to n and is more than or equal to 0.01, and q is (4-3 n)/2; m is selected from Al and/or Mn element, G is selected from at least one element in the IIA-IIIA groups of the 2-5 periods, R is selected from at least one element of B, mg, ca, sr, Y, ti, V, cr, fe, cu, zr, W, nb and Al;

preferably, 0.95. Ltoreq. E.ltoreq.1.2, x.ltoreq.1-x-y-z-m, y.ltoreq.1-x-y-z-m, 0.6. Ltoreq.1-x-y-z-m < 0.9,0.05. Ltoreq. 0.2,0.01. Ltoreq. 0.03,0.01. Ltoreq.m < 0.03,0 < n.ltoreq.0.007, q.ltoreq. = (4-3 n)/2; g is at least one element selected from Al, mg, ca, sr, zr, nb and Mo;

preferably, the lithium iron manganese phosphate material has a composition represented by formula II:

Li _i Mn _1-h-k-j Fe _h D _k D' _j (PO ₄ ) /C formula II;

wherein h is more than 0.1 and less than or equal to 0.4,0 and more than or equal to 0.04,0, j is more than or equal to 0.04,0.9, i is more than or equal to 1.2; d is at least one element selected from Mg, co, ni, cu, zn and Ti, and D' is at least one element selected from Mg, ca, sr, ti, V, cr, co, ni, cu, zn, zr, Y, mo, nb, B, al, W, la and Sm; based on the total weight of the lithium iron manganese phosphate material, the weight of the carbon element accounts for 5-12%;

preferably, 0.15 < h ≦ 0.35,0.01 ≦ k ≦ 0.03,0.01 ≦ j ≦ 0.03,1 < i ≦ 1.1; d is at least one element selected from Mg, cu and Ti; d' is at least one element selected from Ti, nb and B; based on the total weight of the lithium iron manganese phosphate material, the weight ratio of the carbon element is 8-10%.

4. The composite positive electrode material according to any one of claims 1 to 3, wherein the average particle diameter D of the composite positive electrode material ₅₀ Is 1-20 μm, preferably 2-10 μm;

preferably, the composite positive electrode material is a composite positive electrode material which takes a multi-element material as a core and takes lithium manganese iron phosphate as a coating layer;

preferably, the average particle diameter D of the multi-component material ₅₀ Is 1-20 μm, preferably 2-10 μm;

preferably, the average thickness of the coating layer is 10-400nm, preferably 50-300nm;

preferably, the weight ratio of the multi-component material to the lithium iron manganese phosphate material is 1 to 9:1, preferably 1.5 to 4:1, based on the total weight of the composite cathode material.

5. The preparation method of the composite cathode material is characterized by comprising the following steps of:

step 1: preparation of multicomponent materials

step 2: preparation of lithium manganese iron phosphate material

(3) Mixing a lithium iron manganese phosphate material precursor, a second lithium source, a first carbon source and an additive L1, homogenizing, drying and carrying out secondary calcination to obtain the lithium iron manganese phosphate material;

and step 3: preparation of composite cathode material

6. The production method according to claim 5, wherein the conditions of the second heat treatment include: under the oxygen-containing atmosphere, the heat treatment temperature is 150-300 ℃, the heat treatment time is 2-4h, and the oxygen concentration in the oxygen-containing atmosphere is more than or equal to 8vol%.

7. The production method according to claim 5 or 6, wherein, in the step (1), the additive N1 is a compound containing a doping element G selected from at least one element from groups IIA to IIIA of periods 2 to 5, further preferably, the doping element G is selected from at least one element from Al, mg, ca, sr, zr, nb and Mo;

preferably, the additive N2 is a compound containing a doping element R selected from at least one element of B, mg, ca, sr, Y, ti, V, cr, fe, cu, zr, W, nb and Al;

preferably, the first carbon source is selected from at least one of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol and dopamine, further preferably, the first carbon source is selected from at least one of glucose, sucrose, starch and cellulose;

preferably, the additive L1 is a compound containing a doping element D 'selected from at least one element of Mg, ca, sr, ti, V, cr, co, ni, cu, zn, zr, Y, mo, nb, B, al, W, la and Sm, and further preferably, the doping element D' is selected from at least one element of Ti, nb and B.

8. The production method according to any one of claims 5 to 7,

the multi-element material precursor contains Ni, co and M elements, wherein M is selected from Al and/or Mn elements;

in step (1), the multinary material is calculated by [ n (Ni) + n (Co) + n (M) ], the first lithium source is calculated by n (Li), and the amount of the first lithium source is 0.9 ≦ n (Li) ]/[ n (Ni) + n (Co) + n (M) ] ≦ 1.3; the dosage of the additive N1 is calculated by N (G) and is more than or equal to [ N (G) ]/[ N (Ni) + N (Co) + N (M) ] < 0.05;

preferably, said multinary material is calculated as [ n (Ni) + n (Co) + n (M) ], said first lithium source is calculated as n (Li), said first lithium source is used in an amount such that 0.95 ≦ n (Li) ]/[ n (Ni) + n (Co) + n (M) ] ≦ 1.2; the additive N1 is used in an amount of 0.01 to [ N (G) ]/[ N (Ni) + N (Co) + N (M) ] < 0.03, calculated as N (G);

preferably, in step (2), the first calcined material, in terms of [ N (Ni) + N (Co) + N (M) ], and the additive N2, in terms of N (R), are used in amounts such that 0 ≦ N (R) ]/[ N (Ni) + N (Co) + N (M) ] < 0.05, more preferably, 0.01 ≦ N (R) ]/[ N (Ni) + N (Co) + N (M) ] < 0.03;

preferably, the lithium iron manganese phosphate material precursor comprises Mn, fe and D elements, wherein D is at least one element selected from Mg, co, ni, cu, zn and Ti;

preferably, in the step (3), the lithium iron manganese phosphate material precursor and the second lithium source are used in an amount of 0.9 < [ n (Li) ]/[ n (Mn) + n (Fe) + n (D) ] ≦ 1.2; the additive L1 is used in an amount of 0 < [ n (D') ]/[ n (Mn) + n (Fe) + n (D) ] < 0.04;

preferably, in the step (3), the lithium iron manganese phosphate material precursor and the second lithium source are used in an amount of 1 < [ n (Li) ]/[ n (Mn) + n (Fe) + n (D) ] < 1.1; the additive L1 is used in an amount of 0.01 to [ n (D') ]/[ n (Mn) + n (Fe) + n (D) ] < 0.03;

preferably, in the step (3), the weight ratio of the lithium iron manganese phosphate material precursor to the first carbon source is 1:0.05 to 0.12, preferably 1:0.06-0.1.

9. The production method according to any one of claims 5 to 8, wherein in step (1), the conditions of the first calcination include: in an oxygen-containing atmosphere, the calcination temperature is 650-900 ℃, preferably 700-850 ℃, the calcination time is 6-30h, preferably 8-25h, the oxygen concentration in the oxygen-containing atmosphere is more than or equal to 4vol%, preferably more than or equal to 8vol%;

preferably, the conditions of the first heat treatment in step (2) include: under the oxygen-containing atmosphere, the heat treatment temperature is 300-480 ℃, preferably 320-460 ℃, the heat treatment time is 5-15h, preferably 6-12h, the oxygen concentration in the oxygen-containing atmosphere is more than or equal to 4vol%, preferably the oxygen concentration is more than or equal to 8vol%;

preferably, in step (3), the conditions of the second calcination include: under the protective atmosphere, the calcining temperature is 600-700 ℃, preferably 620-660 ℃, and the calcining time is 8-12 h, preferably 9-11 h.

10. A composite positive electrode material produced by the production method according to any one of claims 5 to 9.

11. A lithium ion battery comprising the composite positive electrode material according to any one of claims 1 to 4 and 10.