CN111384371A

CN111384371A - Compression-resistant positive active material and electrochemical energy storage device

Info

Publication number: CN111384371A
Application number: CN201811637371.5A
Authority: CN
Inventors: 杜锐; 刘勇超; 赵德宇; 王嗣慧; 沈重亨; 柳娜
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2018-12-29
Filing date: 2018-12-29
Publication date: 2020-07-07
Anticipated expiration: 2038-12-29
Also published as: CN111384371B

Abstract

The invention relates to the technical field of batteries, in particular to a pressure-resistant positive electrode active material and an electrochemical energy storage device. The positive electrode canThe material includes secondary particles composed of primary particles, the number σ of the primary particles in unit spherical area in SEM spectrum of the secondary particles is 5/μm²About 30 pieces/. mu.m²The single-particle compressive strength of the secondary particles is 60MPa to 300MPa, and the molecular formula of the positive active material is Li_xNi_yCo_zM_kMe_pO_rA_mX is more than or equal to 0.95 and less than or equal to 1.05, Y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, k is more than or equal to 0 and less than or equal to 1, r is more than or equal to 2, M is more than or equal to 0 and less than or equal to 2, M + r is less than or equal to 2, M is selected from Mn and/or Al, Me is selected from one or more combinations of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W and Nb, and A is selected from one or more combinations of N, F, S, Cl. The positive active material has compact particle structure and higher single-particle compressive strength, and a lithium ion battery using the positive active material has good cycle performance, lower volume expansion rate and good dynamic performance.

Description

Compression-resistant positive active material and electrochemical energy storage device

Technical Field

The invention relates to the technical field of batteries, in particular to a pressure-resistant positive electrode active material and an electrochemical energy storage device.

Background

With the continuous upgrade of energy crisis and environmental problems, the development of new green energy is urgent. Lithium ion batteries have the advantages of high specific energy, wide application temperature range, low self-discharge rate, long cycle life, good safety performance, no pollution and the like, and are currently applied to various fields. Lithium ion batteries have been gradually tried around the world as an energy system for automobiles to replace conventional diesel locomotives. However, currently used lithium iron phosphate (LiFePO)₄) Low nickel ternary (LiNi)_1/3Co_1/3Mn_1/3O₂) And the like, due to the property limitation of the material, the requirement of the power battery on the energy density of the lithium ion battery anode active material cannot be completely met. Increase the content of nickel IIIThe nickel content of the element anode material can improve the energy density of the battery, so the high-nickel ternary anode material is one of the main research objects of the current power battery. However, as the content of nickel increases, the direct side reaction between the positive electrode active material and the electrolyte is also significantly increased, and the cycle performance is significantly deteriorated, which is one of the bottlenecks in mass production and commercialization at present.

At present, on the material level, the main means for solving the problem of cycle performance is the main element content optimization, doping increase and coating modification technology. The three measures can improve the cycle performance to a certain degree, but still have gap with the market demand. The polycrystalline high-nickel ternary material has high nickel content and strong surface activity, is easy to generate side reaction with electrolyte, so that the cycle performance of a battery core is obviously deteriorated, and is one of the main difficulties in the current market application. Through research, the ternary cathode material has a particle cracking phenomenon in a circulation process, and the cell failure analysis finds that the particle cracking is a main reason for deterioration of the cell circulation performance. Therefore, how to improve the particle crushing problem in the circulating process is particularly important for improving the circulating performance.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a positive active material with a compact structure and good compressive strength, and an electrochemical energy storage device using the same, wherein the positive active material with excellent mechanical strength and good ion conductivity is used to improve the cycle life of the battery, control the volume expansion rate during the cycle process, and improve the dynamic performance of the battery.

To achieve the above and other related objects, an aspect of the present invention provides a cathode active material including secondary particles composed of primary particles, the number σ of the primary particles per unit area in an SEM spectrum of the secondary particles being 5 particles/μm²About 30 pieces/. mu.m²The single-particle compressive strength of the positive active material is 60 MPa-300 MPa, and the molecular formula of the positive active material is Li_xNi_yCo_zM_kMe_pO_rA_m，0.95≤x≤1.05，0≤y≤1，0≤z≤1，0≤k≤1P is more than or equal to 0 and less than or equal to 0.1, r is more than or equal to 1 and less than or equal to 2, M is more than or equal to 0 and less than or equal to 2, M + r is less than or equal to 2, M is selected from Mn and/or Al, Me is selected from one or more of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W and Nb, and A is selected from one or more of N, F, S, Cl.

Another aspect of the present invention provides a cathode material, including the cathode active material of the present invention, the surface of the cathode active material is provided with an outer cladding layer, the outer cladding layer includes a cladding element, and the cladding element of the outer cladding layer is selected from one or more combinations of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P.

Another aspect of the present invention provides a method for determining the number of primary particles per unit sphere surface area of secondary particles in the positive electrode active material or the positive electrode material of the present invention, comprising the steps of:

(1) selecting the average particle diameter D of the secondary particles_vPerforming SEM detection on 50 +/-20% of positive active material samples to obtain SEM spectra under 10K times;

(2) calculating the number σ of primary particles in the surface area of a unit sphere in the positive electrode active material according to the SEM spectrum obtained in the step (1) by the following formula:

σ＝(x1+x2)/2*(y1+y2)/2/(A/C*B/C)

wherein the content of the first and second substances,

x1 represents the number of primary particles in the transverse direction of the lower edge of the picture in an SEM picture of the secondary particles by a factor of 10K;

x2 represents the number of primary particles in the lateral direction of the upper edge of the picture in the SEM image of the secondary particles by a factor of 10K;

y1 represents the number of primary particles in the longitudinal direction at the left edge of the picture in an SEM picture of 10K times the number of secondary particles;

y2 represents the number of primary particles in the longitudinal direction at the right edge of the picture in an SEM picture of a multiple of 10K of the secondary particles;

a represents the actual measured length in mm in the transverse direction of the SEM image of the secondary particle by a factor of 10K;

b represents the actual measured length in mm of the longitudinal direction of the SEM image of the secondary particle by a factor of 10K;

c represents the corresponding actual measured length in mm/μm at a scale of 1 μm in an SEM image of the secondary particles at a magnification of 10K;

when the number of primary particles in the SEM image of the secondary particles by a factor of 10K is calculated, one primary particle is calculated as long as a part of the primary particles appears.

Another aspect of the invention provides an electrochemical energy storage device comprising the positive electrode active material or positive electrode material of the invention.

Compared with the prior art, the invention has the beneficial effects that:

the positive active material comprises secondary particles consisting of primary particles, the secondary particles are compact in structure, high in compressive strength and moderate in ion transmission distance, the problem of particle cracking in the circulating process can be effectively solved, the problem of gas generation caused by particle crushing is avoided, and the ion conducting performance is excellent, so that a lithium ion battery using the positive active material has good circulating performance, low volume expansion rate and good dynamic performance.

Drawings

FIG. 1 is a graph showing the compressive strength of pellets of example 4 of the present invention.

FIG. 2 is a graph showing the compression strength of comparative example 3 granules of the present invention.

FIG. 3 is a diagram of the compression strength testing apparatus of the present invention.

FIG. 4 is an SEM image of particles of example 1 of the present invention at a magnification of 10K.

Detailed Description

The positive electrode active material, the positive electrode material, and an electrochemical energy storage device using the positive electrode active material or the positive electrode material according to the present invention are described in detail below.

The first aspect of the invention provides a positive electrode active material comprising secondary particles composed of primary particles, the number σ of the primary particles in a unit spherical surface area in an SEM spectrum of the secondary particles being 5 particles/μm²About 30 pieces/. mu.m²The single-particle compressive strength of the secondary particles is 60MPa to 300MPa, and the molecular formula of the positive active materialIs Li_xNi_yCo_zM_kMe_pO_rA_mX is more than or equal to 0.95 and less than or equal to 1.05, Y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, k is more than or equal to 0 and less than or equal to 1, r is more than or equal to 2, M is more than or equal to 0 and less than or equal to 2, M + r is less than or equal to 2, M is selected from Mn and/or Al, Me is selected from one or more combinations of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W and Nb, and A is selected from one or more combinations of N, F, S, Cl. The positive active material of the lithium metal transition oxide is secondary particles consisting of primary particles, and compared with single crystal particles, the polarization of the secondary particles is smaller, so that the internal resistance of the lithium ion battery can be effectively reduced; however, because certain gaps exist among primary particles in the secondary particles and different synthesis processes lead to obvious differences in binding force among the primary particles, the compactness of the surface structure of the secondary particles can be improved by controlling the number of the primary particles in the unit sphere surface area of the surface layer of the secondary particles. The positive active material has the advantages of higher compactness of the surface structure, excellent single-particle compressive strength and moderate ion transmission distance, can improve the particle cracking problem in the circulating process, and simultaneously ensures that the ion conducting performance of the positive active material is good, thereby ensuring that a lithium ion battery using the positive active material has good circulating performance, lower volume expansion rate and good dynamic performance.

In the positive active material provided by the invention, the positive active material is a lithium transition metal oxide, and because certain element content segregation exists in the preparation process, lithium element in the molecular formula of the positive active material may have a situation of lithium deficiency or lithium enrichment to a certain extent, when the relative content range of the lithium element is more than or equal to 0.95 and less than or equal to 1.05, the influence on the capacity of the positive active material is not large, and optionally, the relative content of the lithium element is more than or equal to 0.95 and less than or equal to 1, and x is more than or equal to 1 and less than or equal to 1.05.

In the positive electrode active material provided by the present invention, preferably, the positive electrode active material is a ternary lithium transition metal oxide containing at least one element of Ni, Co, Mn or Al, and the molecular formula of the positive electrode active material is as follows: y is more than 0 and less than 1, z is more than 0 and less than 1, k is more than 0 and less than 1, p is more than or equal to 0 and less than or equal to 0.1, r is more than or equal to 1 and less than or equal to 2, m is more than or equal to 0 and less than or equal to 2, and m + r is less than or equal to 2.

In a further preferred embodiment of the present invention, the positive electrode active material is a high nickel positive electrode active material, and the molecular formula of the positive electrode active material is 0.50<y is less than or equal to 0.95, z is less than or equal to 0.05 and less than or equal to 0.2, k is less than or equal to 0.05 and less than or equal to 0.4, and p is less than or equal to 0 and less than or equal to 0.05. Specifically, the positive electrode active material may be LiNi_1/3Co_1/3Mn_1/3O₂、LiNi_0.5Co_0.2Mn_0.3O₂、LiNi_0.5Co_0.25Mn_0.25O₂、LiNi_0.55Co_0.15Mn_0.3O₂、LiNi_0.55Co_0.1Mn_0.35O₂、LiNi_0.55Co_0.05Mn_0.4O₂、LiNi_0.6Co_0.2Mn_0.2O₂、LiNi_0.75Co_0.1Mn_0.15O₂、LiNi_0.8Co_0.1Mn_0.1O₂、LiNi_0.85Co_0.05Mn_0.1O₂、LiNi_0.88Co_0.05Mn_0.07O₂、LiNi_0.9Co_0.05Mn_0.05O₂、LiNi_0.72Co_0.18Al_0.1O₂、LiNi_0.81Co_0.045Mn_0.045Al_0.1O₂The active material may be obtained by modifying the above substances by partial substitution with Me and/or a, wherein Me is selected from a combination of one or more of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, and Nb, and a is selected from a combination of one or more of N, F, S, Cl.

More preferably, in the molecular formula of the positive electrode active material, y is more than or equal to 0.70 and less than or equal to 0.95, z is more than or equal to 0 and less than or equal to 0.2, k is more than or equal to 0 and less than or equal to 0.2, and p is more than or equal to 0 and less than or equal to 0.05.

According to the invention, the positive active material with higher nickel content is selected from the positive active materials, and the higher the relative content of Ni element is, the higher the theoretical gram capacity of the material is, so that the volume energy density of the battery can be effectively improved, but the surface residual lithium content of the high-nickel positive active material is higher, and the particles are more easily crushed, and by controlling the surface compactness of secondary particles and the compressive strength of single particles of the high-nickel positive active material, the gas generation problem of the high-capacity battery in the circulation process can be effectively solved, and the energy density and the service life of the battery are improved.

In the positive electrode active material provided by the invention, the single-particle compressive strength of the secondary particles means that the particle size is in the average particle size D _v50 fluctuation 10% up and down, single secondary particle as single particle, under external force, minimum pressure at crushing ". The single-particle compressive strength of the secondary particles in the invention is selected from 60 MPa-300 MPa, 60 MPa-80 MPa, 80 MPa-100 MPa, 100 MPa-120 MPa, 120 MPa-150 MPa, 150 MPa-180 MPa, 180 MPa-200 MPa, 200 MPa-220 MPa, 220 MPa-240 MPa, 240 MPa-260 MPa, 260 MPa-280 MPa and 280 MPa-300 MPa.

In the positive active material provided by the invention, the powder compaction density of the positive active material is not less than 3.3g/cm³. The positive active material has good compression resistance and high powder compaction density, so that the positive active material can bear larger pressure without breaking in the manufacturing process of the pole piece, and is beneficial to improving the compaction density of the positive pole piece and improving the volume energy density of a battery.

In the positive electrode active material provided by the present invention, D of the secondary particles_v10 is 2 to 8 μm, D _v50 is 5 to 18 μm, D_v90 is 10 to 30 μm. Optionally, D_v10 is 2 to 3 μm, 3 to 4 μm, 4 to 5 μm, 5 to 6 μm, 6 to 7 μm, 7 to 8 μm, D _v50 is 5 to 18 μm, 5 to 8 μm, 8 to 10 μm, 10 to 12 μm, 12 to 15 μm, 15 to 18 μm, D_v90 is 10 to 30 μm, 10 to 15 μm, 15 to 20 μm, 20 to 25 μm, or 25 to 30 μm.

In the positive electrode active material provided by the invention, the secondary particles are obtained by stacking primary particles in the extending direction of the primary particles, the primary particles are rod-shaped, conical or needle-shaped, and the primary particles extend and stack in the radial direction to form the secondary particles. The length of the primary particles is 100 nm-1000 nm, and the width of the cross section is 50 nm-400 nm. Optionally, the length of the primary particles is 100 nm-1000 nm, 100 nm-200 nm, 200 nm-300 nm, 300 nm-400 nm, 400 nm-500 nm, 500 nm-600 nm, 600 nm-700 nm, 700 nm-800 nm, 800 nm-900 nm and 900 nm-1000 nm; the width of the section is 50 nm-400 nm, 50 nm-100 nm, 100 nm-150 nm, 150 nm-200 nm, 200 nm-300 nm, 300 nm-350 nm and 350 nm-400 nm.

As a preferable mode of the present invention, the ratio of the length of the primary particles to the width of the radial cross section is 2 to 20, 2 to 5, 5 to 8, 8 to 10, 10 to 12, 12 to 15, 15 to 18, 18 to 20.

In the positive electrode active material provided by the present invention, the secondary particle has a BET of 0.3m²/g～0.8m²/g、0.3m²/g～0.4m²/g、0.4m²/g～0.5m²/g、0.5m²/g～0.6m²/g、0.6m²/g～0.7m²/g、0.7m²/g～0.8m²/g。

In the positive active material provided by the invention, when the volume particle size distribution of the secondary particles is in the range, the specific surface area of the positive active material can be ensured to be lower, and the ion transmission distance is moderate. When the particle size of secondary particle was in above-mentioned scope, the ratio of the length of further control primary particle, width and length and radial cross section width was in above-mentioned scope, can guarantee that the surface and the inner structure of secondary particle who forms have higher density, and the transmission distance of lithium ion between primary particle is moderate, still is favorable to promoting the mechanical strength of secondary particle.

In the positive electrode active material provided by the invention, at least part of the primary particle surfaces at the non-outermost layer positions in the secondary particles are provided with the inner coating layer, the inner coating layer comprises a coating element, and the coating element of the inner coating layer is selected from one or more of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B and P. The coating element of the inner coating layer is not represented by the molecular formula Li of the positive active material_xNi_yCo_zM_kMe_pO_rA_mIn general, the cladding element of the inner cladding layer does not enter the crystal lattice.

In a preferred embodiment of the present invention, the coating element of the inner coating layer is at least two or more selected from Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P. According to the invention, the inner cladding layer on the surface of the primary particle contains at least two or more oxides formed by the elements, so that the stability of the inner cladding layer attached to the surface of the primary particle can be improved, the inner cladding layer has certain ion conductivity and electron conductivity, and the influence of the inner cladding layer on the polarization problem of the anode active material is reduced, so that the direct contact of the anode active material and electrolyte is effectively avoided, the side reaction with the electrolyte is reduced, a large amount of gas in the circulation process is avoided, and meanwhile, the low impedance, excellent circulation and rate performance of the battery are ensured.

The invention provides a positive electrode material, which comprises the positive electrode active material of the first aspect, wherein the surface of the positive electrode active material is provided with an outer coating layer, and the coating element of the outer coating layer is selected from one or more of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B and P.

In a preferred embodiment of the present invention, the surface of the positive electrode material is provided with an outer coating layer, and at least a part of the surfaces of the primary particles other than the outermost layer of the secondary particles is provided with an inner coating layer. Further preferably, the outer cladding is the same as the cladding material of the inner cladding.

In a preferred embodiment of the present invention, the coating element of the outer cladding layer is at least two or more selected from Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P. According to the invention, the outer coating layer on the surface of the positive active material contains at least two or more oxides formed by the elements, so that the stability of the outer coating layer attached to the surface of the positive active material can be improved, the outer coating layer has certain ion conductivity and conductivity, and the influence of the outer coating layer on the polarization problem of the positive active material is reduced, so that the direct contact of the positive active material and electrolyte is effectively avoided, the side reaction with the electrolyte is reduced, a large amount of gas in the circulation process is avoided, and meanwhile, the low impedance and excellent circulation and rate performance of the battery are ensured.

In the cathode material provided by the invention, the outer cladding layer is a continuous and/or discontinuous layered cladding layer; preferably, the outer cladding layer is a composite of a continuous first cladding layer and a discontinuous second cladding layer, and more preferably, the discontinuous cladding layer is formed of a different material than the continuous cladding layer. Wherein, the elements forming the discontinuous coating layer are selected from one or a combination of more of Al, Ba, Zn, Ti and Co, and the elements forming the continuous coating layer are selected from one or a combination of more of W, Y, Si, B, P and Sn.

In the anode material provided by the invention, the discontinuous layered coating can be a discrete island-shaped outer coating, and the discontinuous coating can play a role similar to a nano nail on the surface of the anode active material, so that the discontinuous layered coating can be firmly combined with the anode active material, the probability of crushing anode active material particles in a circulating process is effectively reduced, and meanwhile, the discontinuous layered coating can also enhance the binding force between primary particles of the anode active material and the primary particles, so that the integral mechanical strength of the anode active material (particularly in a secondary particle form formed by agglomeration of the primary particles) is increased, and the anode active material is not easy to crush. Meanwhile, a continuous coating layer is formed on the surface of the positive active material, so that the roughness of the surface of the positive material can be effectively reduced, the specific surface area of the positive material is reduced, the effective contact area of the surface of the positive material and electrolyte is further reduced, the side reaction of the surface of the positive material and the electrolyte is reduced, and the generation of a large amount of gas due to the side reaction of the surface of the positive material and the electrolyte is avoided.

A third aspect of the present invention provides a method for determining the number of primary particles per unit sphere surface area of secondary particles in the positive electrode active material according to the first aspect of the present invention or the positive electrode material according to the second aspect of the present invention, comprising the steps of:

(2) calculating the number σ (number of primary particles/μm) per unit area in the positive electrode active material from the SEM spectrum obtained in step (1) by the following formula²)：

σ＝(x1+x2)/2*(y1+y2)/2/(A/C*B/C)

Wherein the content of the first and second substances,

Compared with the method for representing the grain sizes of the primary particles and the secondary particles only and calculating the number of the primary particles in an SEM image under 10K times of the secondary particles, the method is an effective way for objectively representing the compaction degree of the spherical structure of the secondary particles consisting of the primary particles.

A fourth aspect of the invention provides a method for producing the positive electrode active material of the first aspect of the invention, which should be known to those skilled in the art, and may include, for example: those skilled in the art can select appropriate raw materials and proportions of the positive electrode active material according to the elemental composition of the positive electrode active material. For example, the raw material of the positive electrode active materialTernary material precursors of nickel, cobalt, manganese and/or aluminum, lithium sources, Me sources, a sources and the like can be included, and the proportion of each raw material is generally proportioned according to the proportion of each element in the positive electrode active material. More specifically, the ternary material precursor may be one including, but not limited to, Ni_1/3Co_1/3Mn_1/3(OH)₂、Ni_0.5Co_0.2Mn_0.3(OH)₂、Ni_0.5Co_0.25Mn_0.25(OH)₂、Ni_0.55Co_0.15Mn_0.3(OH)₂、Ni_0.55Co_0.1Mn_0.35(OH)₂、Ni_0.55Co_0.05Mn_0.4(OH)₂、Ni_0.6Co_0.2Mn_0.2(OH)₂、Ni_0.75Co_0.1Mn_0.15(OH)₂、Ni_0.8Co_0.1Mn_0.1(OH)₂、Ni_0.88Co_0.05Mn_0.07(OH)₂、0.9Ni_0.8Co_0.2(OH)₂·0.1Al(OH)₃、0.9Ni_0.9Co_0.05Mn_0.05(OH)₂·0.1Al(OH)₃The lithium source may be a lithium-containing compound, which may include, but is not limited to, LiOH₂O、LiOH、Li₂CO₃、Li₂O and the like, the Me source can be generally one or more of Me element-containing compounds, the Me element-containing compounds can be one or more of oxides, nitrates and carbonates containing at least one element of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W and Nb, the A source can be A element-containing compounds, and the A element-containing compounds can be compounds including but not limited to LiF, NaCl, Na₂S、Li₃N, etc. For another example, the sintering conditions may be 800 ℃ and an oxygen concentration of 20% or more.

The method for preparing the cathode active material may further include providing an inner coating layer on the surface of the primary particles at least partially at a position other than the outermost layer of the secondary particles, and the method for forming the inner coating layer on the surface of the primary particles may be known to those skilled in the art, and may include, for example: the primary particles are sintered in the presence of a compound containing a coating element to form an inner coating layer on the surfaces of the primary particles. For another example, when the inner coating material is the same as the outer coating material, the inner coating process and the outer coating process may be combined into a one-step process, and the coating material may pass through the pores on the surface and inside of the secondary particles to simultaneously coat the outer surface and at least a portion of the inner primary particles. Those skilled in the art can select the kind, proportion and sintering conditions of the compound containing the coating element according to the parameters such as the composition of the inner coating layer, the powder compressive strength of the positive electrode active material, the resistivity of the powder and the like. For example, the compound containing a coating element may be an oxide, nitrate, phosphate, carbonate, or the like containing one or more elements of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P, and for example, the compound containing a coating element may be used in an amount of 0.01% to 0.5%, and further for example, the sintering may be performed under a high temperature of 200 ℃ to 700 ℃.

A fifth aspect of the invention provides a method for producing the positive electrode material of the second aspect of the invention, comprising: an outer coating layer is formed on the surface of the positive electrode active material of the first aspect of the invention.

A method of forming an outer cladding layer on the surface of the positive electrode active material should be known to those skilled in the art, and may include, for example: the positive electrode active material is sintered in the presence of a compound containing a coating element to form an outer coating layer on the surface of the positive electrode active material. The skilled in the art can select the kind, proportion and sintering condition of the compound containing the coating element according to the parameters of the composition of the outer coating layer, the powder compressive strength of the positive active material, the resistivity of the powder and the like. For example, the compound containing a coating element may be an oxide, nitrate, phosphate, carbonate, or the like containing one or more elements of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P, and for example, the compound containing a coating element may be used in an amount of 0.01% to 0.5%, and further for example, the sintering may be performed under a high temperature of 200 ℃ to 700 ℃.

A sixth aspect of the invention provides an electrochemical energy storage device comprising the positive electrode active material of the first aspect of the invention or the positive electrode material of the second aspect of the invention.

In the electrochemical energy storage device according to the sixth aspect of the present invention, it should be noted that the electrochemical energy storage device may be a super capacitor, a lithium ion battery, a lithium metal battery, or a sodium ion battery. In the embodiments of the present invention, only the embodiment in which the electrochemical energy storage device is a lithium ion battery is shown, but the present invention is not limited thereto.

The lithium ion battery comprises a positive pole piece, a negative pole piece, an isolating membrane and electrolyte, wherein the isolating membrane is arranged between the positive pole piece and the negative pole piece at intervals, and the positive pole piece comprises the positive active material in the first aspect of the invention or the positive material in the second aspect of the invention. Methods of preparing the lithium ion battery are known to those skilled in the art, and for example, the positive electrode sheet, the separator, and the negative electrode sheet may each be a laminate so as to be cut into a target size and then stacked in sequence, and may be wound to a target size for forming a cell, and may be further combined with an electrolyte to form a lithium ion battery.

In the lithium ion battery, the positive electrode plate comprises a positive electrode current collector and a positive electrode material layer positioned on the positive electrode current collector, wherein the positive electrode material layer comprises the positive electrode active material of the first aspect of the invention or the positive electrode material of the second aspect of the invention, a binder and a conductive agent. The person skilled in the art can select a suitable method to prepare the positive electrode sheet, for example, the following steps can be included: the positive electrode active material or the positive electrode material, the binder and the conductive agent are mixed to form slurry, and then the slurry is coated on the positive electrode current collector. The binder typically includes a fluorinated polyolefin-based binder, and water is typically a good solvent relative to the fluorinated polyolefin-based binder, i.e., the fluorinated polyolefin-based binder typically has good solubility in water, for example, the fluorinated polyolefin-based binder may include, but is not limited to, polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers, or modified (e.g., carboxylic acid, acrylic acid, acrylonitrile, etc.) derivatives thereof, and the like. The conductive agent may be various conductive agents suitable for a lithium ion (secondary) battery in the art, and for example, may be a combination including one or more of acetylene black, conductive carbon black, carbon fiber (VGCF), Carbon Nanotube (CNT), ketjen black, and the like, but not limited thereto. The positive electrode current collector may be generally a layer body, and is generally a structure or a part that can collect current, and the positive electrode current collector may be various materials suitable for being used as a positive electrode current collector of a lithium ion battery in the art, for example, the positive electrode current collector may include, but is not limited to, a metal foil, and more specifically, may include, but is not limited to, a copper foil, an aluminum foil, and the like.

In a lithium ion battery, the negative electrode tab generally includes a negative electrode current collector and a negative electrode active material layer on a surface of the negative electrode current collector, and the negative electrode active material layer generally includes a negative electrode active material. The negative active material may be any material suitable for use in negative active materials of lithium ion batteries in the art, and may be, for example, one or more of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based materials, tin-based materials, lithium titanate, or other metals capable of forming an alloy with lithium, and the like. Wherein, the graphite can be selected from one or more of artificial graphite, natural graphite and modified graphite; the silicon-based material can be selected from one or more of elemental silicon, silicon-oxygen compound, silicon-carbon compound and silicon alloy; the tin-based material may be selected from elemental tin, tin-oxygen compounds, tin alloys, or combinations of one or more thereof. The negative electrode current collector is generally a structure or a part for collecting current, and the negative electrode current collector may be any material suitable for use as a negative electrode current collector of a lithium ion battery in the art, for example, the negative electrode current collector may include, but is not limited to, a metal foil, and the like, and more specifically, may include, but is not limited to, a copper foil, and the like.

In a lithium ion battery, the separator may be any of various materials suitable for use in lithium ion battery separators in the art, and may be, for example, one or more combinations including, but not limited to, polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, natural fiber, and the like.

In the lithium ion battery, the electrolyte may be any electrolyte suitable for use in the lithium ion battery in the art, for example, the electrolyte generally includes an electrolyte and a solvent, the electrolyte may generally include a lithium salt and the like, more specifically, the lithium salt may be an inorganic lithium salt and/or an organic lithium salt and the like, and may specifically include, but is not limited to, the lithium salt may be selected from LiPF₆、LiBF₄、LiN(SO₂F)₂(abbreviated LiFSI), LiN (CF)₃SO₂)₂(abbreviated as LiTFSI) and LiClO₄、LiAsF₆、LiB(C₂O₄)₂(abbreviated as LiBOB) and LiBF₂C₂O₄(abbreviated as LiDFOB). For another example, the concentration of the electrolyte may be between 0.8mol/L and 1.5 mol/L. The solvent may be any solvent suitable for the electrolyte of lithium ion battery in the art, and the solvent of the electrolyte is generally a non-aqueous solvent, and preferably may be an organic solvent, and specifically may include, but is not limited to, one or more of ethylene carbonate, propylene carbonate, butylene carbonate, pentylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, and the like, or halogenated derivatives thereof.

The following examples are provided to further illustrate the advantageous effects of the present invention.

In order to make the objects, technical solutions and advantageous technical effects of the present invention more clear, the present invention is further described in detail below with reference to examples. However, it should be understood that the embodiments of the present invention are only for explaining the present invention and are not for limiting the present invention, and the embodiments of the present invention are not limited to the embodiments given in the specification. The examples were prepared under conventional conditions or conditions recommended by the material suppliers without specifying specific experimental conditions or operating conditions.

Furthermore, it is to be understood that one or more method steps mentioned in the present invention does not exclude that other method steps may also be present before or after the combined steps or that other method steps may also be inserted between these explicitly mentioned steps, unless otherwise indicated; it is also to be understood that a combined connection between one or more devices/apparatus as referred to in the present application does not exclude that further devices/apparatus may be present before or after the combined device/apparatus or that further devices/apparatus may be interposed between two devices/apparatus explicitly referred to, unless otherwise indicated. Moreover, unless otherwise indicated, the numbering of the various method steps is merely a convenient tool for identifying the various method steps, and is not intended to limit the order in which the method steps are arranged or the scope of the invention in which the invention may be practiced, and changes or modifications in the relative relationship may be made without substantially changing the technical content.

In the following examples, reagents, materials and instruments used are commercially available unless otherwise specified.

Firstly, preparation of battery

Example 1

1. Preparation of cathode material

1) Preparing nickel sulfate, manganese sulfate and cobalt sulfate into a solution with the concentration of 1mol/L according to the molar ratio of 8:1:1, and preparing a nickel-cobalt-manganese ternary material precursor Ni by using a hydroxide coprecipitation technology_0.8Co_0.1Mn_0.1(OH)₂. In the process of preparing the precursor, the initial pH value during coprecipitation is controlled to be 9.5, the ammonia concentration is controlled to be 0.4M, and the aging time after reaction is controlled to be 5 h.

2) The precursor Ni of the nickel-cobalt-manganese ternary material is prepared_0.8Co_0.1Mn_0.1(OH)₂Li-containing compound LiOH. H₂Placing the O in a mixing device for mixing according to the mol ratio of 1:1.05, then placing the mixture in an atmosphere furnace for sintering at 800 ℃, and obtaining a positive active material matrix through mechanical grinding after cooling; mixing the positive active material matrix with additive Al₂O₃Placing the mixture into a mixing device for mixing according to the mass ratio of 100:0.3, then placing the mixture into an atmosphere furnace for sintering at 450 ℃ to form the finished product Al₂O₃Coating the treated cathode material.

2. Preparation of positive pole piece

Step 1: mixing the prepared positive electrode material, polyvinylidene fluoride serving as a binder and acetylene black serving as a conductive agent according to a mass ratio of 98:1:1, adding N-methyl pyrrolidone (NMP), and uniformly stirring under the action of a vacuum stirrer to obtain positive electrode slurry; uniformly coating the positive electrode slurry on an aluminum foil with the thickness of 12 mu m;

step 2: drying the coated pole piece in an oven at 100-130 ℃;

and step 3: and obtaining the positive pole piece through cold pressing and slitting.

3. Preparation of negative pole piece

Mixing a negative electrode active material graphite, a thickening agent sodium carboxymethyl cellulose, a binding agent styrene butadiene rubber and a conductive agent acetylene black according to a mass ratio of 97:1:1:1, adding deionized water, and obtaining negative electrode slurry under the action of a vacuum stirrer; uniformly coating the negative electrode slurry on a copper foil with the thickness of 8 mu m; and (3) airing the copper foil at room temperature, transferring the copper foil to a 120 ℃ oven for drying for 1h, and then performing cold pressing and slitting to obtain the negative pole piece.

4. Preparation of electrolyte

The organic solvent is prepared by mixing Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC) according to a volume ratio of 20:20:60, dissolving fully dried lithium salt with a concentration of 1mol/L in the organic solvent in an argon atmosphere glove box with a water content of less than 10ppm, and uniformly mixing to obtain the electrolyte.

5. Preparation of the separator

A polypropylene separator film of 12 μm thickness was used.

6. Preparation of the Battery

The positive pole piece, the isolating film and the negative pole piece are sequentially stacked, the isolating film is positioned between the positive pole piece and the negative pole piece to play an isolating role, the positive pole piece and the negative pole piece are wound into a square bare cell, an aluminum plastic film is filled in the bare cell, the bare cell is baked at 80 ℃ to remove water, corresponding non-aqueous electrolyte is injected into the bare cell and sealed, and the finished battery is obtained after the working procedures of standing, hot cold pressing, formation, clamping, capacity grading and the like.

Example 2

The same as example 1, except for the following steps: the pH value of the coprecipitation is adjusted to 10.5, the ammonia concentration is adjusted to 0.3M in the preparation process of the precursor, and the aging time after the reaction is 3 h.

Example 3

The same as example 1 except for the preparation method of the positive electrode material: the pH value of the coprecipitation is adjusted to be 11, the ammonia concentration is 0.2M in the preparation process of the precursor, and the aging time after the reaction is 5 h.

Example 4

The same as example 1 except for the preparation method of the positive electrode material: the pH value of the coprecipitation is adjusted to 10, the ammonia concentration is adjusted to 0.4M in the preparation process of the precursor, and the aging time after the reaction is 2 h.

Example 5

The same as example 1 except for the preparation method of the positive electrode material: the pH value of the coprecipitation is adjusted to 11.5, the ammonia concentration is adjusted to 0.3M, and the aging time after the reaction is 2h in the precursor preparation process.

Example 6

The same as example 1 except for the preparation method of the positive electrode material: the pH value of the coprecipitation is adjusted to 9.8 and the ammonia concentration is adjusted to 0.3M in the preparation process of the precursor, and the aging time after the reaction is 4 h.

Example 7

The same as example 1 except for the preparation method of the positive electrode material: the relative contents of Ni, Co and Mn elements in the precursor are 0.75:0.1:0.15, the pH value is adjusted to 10.2, the ammonia concentration is 0.5M during coprecipitation in the preparation process of the precursor, and the aging time after reaction is 6 h.

Example 8

The same as example 1 except for the preparation method of the positive electrode material: the relative contents of Ni, Co and Mn elements in the precursor are 0.6:0.2:0.2, the pH value is adjusted to 11.5 and the ammonia concentration is adjusted to 0.6M during coprecipitation in the preparation process of the precursor, and the aging time after reaction is 3 hours.

Example 9

The same as example 1 except for the preparation method of the positive electrode material: the relative contents of Ni, Co and Mn elements in the precursor are 0.55:0.15:0.3, the pH value is adjusted to 11.2 and the ammonia concentration is adjusted to 0.3M during coprecipitation in the preparation process of the precursor, and the aging time after reaction is 2 hours.

Example 10

The same as example 1 except for the preparation method of the positive electrode material: the relative contents of Ni, Co and Mn elements in the precursor are 0.33:0.33:0.33, the pH value is adjusted to 10.9, the ammonia concentration is 0.4M during coprecipitation in the preparation process of the precursor, and the aging time after reaction is 3 h.

Comparative example 1

Preparation method of comparative example 1 the preparation method of example 1 as described above was referred to, except for the preparation method of the positive electrode material: the pH value of the coprecipitation is adjusted to be 11, the ammonia concentration is 0.5M in the preparation process of the precursor, and the aging time after the reaction is 6 h.

Comparative example 2

Preparation method of comparative example 2 the preparation method of example 1 as described above was referred to, except for the preparation method of the positive electrode material: in the preparation process of the precursor, the pH value of the coprecipitation is adjusted to be 12, the ammonia concentration is adjusted to be 0.6M, and the aging time after the reaction is 7 h.

Comparative example 3

The manufacturing method of comparative example 3 refers to the manufacturing method of example 1 described above, except for the manufacturing method of the positive electrode material: the pH value of the coprecipitation is adjusted to 10.5, the ammonia concentration is 0.1M in the preparation process of the precursor, and the aging time after the reaction is 6 h.

Second, performance test

The positive electrode materials prepared in examples 1 to 10 and comparative examples 1 to 3 were measured for the compressive strength per unit sphere area of single particle, the number σ of primary particles, the compacted density, and the BET. The test results are shown in Table 2.

1. Method for testing compressive strength

(1) Placing a sample on an object stage;

(2) bringing the indenter down close to the sample at a speed of 0.1 μm/min until contact with the sample is possible;

(3) the pressure and the displacement of the pressure head are recorded at the moment of contact;

(4) continuously pressing the pellets downward at a constant rate until the pellets disintegrate;

2. BET test method

The BET test is carried out by adopting a GB/T19587-.

3. Compaction density testing method

The test of the compaction density is carried out by adopting a test method of GB/T2433integral 2009 of graphite cathode materials of lithium ion batteries on the national standard, and the test pressure is 5 tons.

4. Method for measuring number of primary particles

The SEM image of 10K times for the sample prepared in example 1 for testing the number of primary particles per unit area in the secondary particles is shown in fig. 4, and the product primary particles are calculated as follows.

The number of primary particles per unit area of 1 μm × 1 μm was calculated according to the formula σ ═ x1+ x2)/2 × (y1+ y2)/2/(a/C × B/C), and the calculation results are shown in table 1.

σ₁(32+ 32)/2/(22 +23)/2/(112/10 × 75/10) 8.5 pieces/μm²。

The calculation methods of other examples and comparative examples are the same, and the calculation results are shown in Table 2.

TABLE 1 number of primary particles per unit sphere surface area of example 1

5. Method for testing cycle performance of battery

Charging to 4.2V at 2.8V-4.2V under a constant temperature environment of 45 ℃ according to 1C, then charging to a current of less than or equal to 0.05mA at a constant voltage under 4.2V, standing for 5min, then discharging to 2.8V according to 1C, recording the capacity as Dn (n is 0,1,2 … …), repeating the previous process until the capacity is attenuated to 80% of the initial capacity, and recording the number of cycle turns of the lithium ion battery. The results of examples 1 to 10 and comparative examples 1 to 3 are shown in Table 3.

6. High-temperature gas production test method of battery

After fully charging the battery to 4.2V at 1C, the battery was left to stand in an incubator at 70 ℃ for 30 days. And measuring the initial volume and the volume after standing for 30 days by a drainage method to obtain the volume expansion rate of the battery.

The volume expansion ratio (%) of the battery (volume after standing for 30 days/initial volume-1) × 100%.

The test results are shown in Table 3.

7. 1/3C capacity test method

Standing the lithium ion battery for 2 hours in a constant temperature environment of 25 ℃, then charging to 4.2V at 2.8V-4.2V according to 1/3C, then charging to a current of less than or equal to 0.05mA at a constant voltage of 4.2V, standing for 5min, then discharging to 2.8V according to 1C, and recording the capacity of the lithium ion battery; dividing the capacity test value by the mass of the anode material in the lithium ion battery to obtain the 1/3C capacity of the anode material. The test results are shown in Table 3.

TABLE 2 characterization of powders of positive active materials of examples 1 to 10 and comparative examples 1 to 3

TABLE 3 electrochemical performance test results of the batteries of examples 1-10 and comparative examples 1-3

From tables 2 and 3, it can be found that: the relative contents of the elements Ni, Co and Mn in the positive electrode materials of examples 1 to 6 and comparative examples 1 to 3 are the same, and since the number of primary particles in the unit sphere area and the compressive strength of a single particle of the positive electrode materials of examples 1 to 6 are within a specific range, the particle microstructures of the positive electrode materials of examples 1 to 6 are compact, the powder material has high mechanical strength and good capacity exertion, and the particles are not easy to break in the preparation or circulation process of the electrode sheet. The cycle performance of the lithium ion batteries prepared by the cathode materials in the embodiments 1-6 is obviously higher than that of the lithium ion batteries prepared by the comparative examples 1-3, and the volume expansion rate in the cycle process is obviously reduced. The positive electrode material in the comparative example 1 has moderate number of primary particles in unit sphere area and low compressive strength of the single particles, which shows that the bonding force among the primary particles in the secondary particles is weak, so that the compaction of the prepared positive electrode plate is difficult to improve; meanwhile, secondary particles are easy to break in the cold pressing and circulating processes of the pole piece, so that a large amount of fresh surfaces in the positive electrode material are in direct contact with the electrolyte, and accordingly gas generation is serious and the circulating performance is poor. In comparative example 2, the number of primary particles in the unit sphere area of the single particle of the positive electrode material is low, and the compressive strength of the single particle is too high, which indicates that the size of the primary particles in the secondary particles is too large and the pores between adjacent primary particles are less, resulting in high polarization and low ion transmission rate of the positive electrode material, and thus the internal resistance of the battery is high, and the cycle performance of the battery is deteriorated. In comparative example 3, the number of primary particles in the unit sphere area of the positive electrode material is too high, and the compressive strength of the single particles is moderate, which indicates that the size of the primary particles in the secondary particles of the positive electrode material is low and the BET is high, so that the gas yield of the formed lithium ion battery is still high and the cycle performance is poor.

In examples 7 to 10, the relative contents of Ni, Co, and Mn elements in the lithium transition metal oxide in the positive electrode material were different, the number of primary particles in the unit sphere area of the positive electrode material and the compressive strength of a single particle were within a specific range, and the discharge capacity of the lithium ion battery was slightly reduced with the decrease in Ni content, but the cycle performance and gas generation problems were significantly optimized.

While the invention has been described with respect to a preferred embodiment, it will be understood by those skilled in the art that the foregoing and other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention. Those skilled in the art can make various changes, modifications and equivalent arrangements, which are equivalent to the embodiments of the present invention, without departing from the spirit and scope of the present invention, and which may be made by utilizing the techniques disclosed above; meanwhile, any changes, modifications and variations of the above-described embodiments, which are equivalent to those of the technical spirit of the present invention, are within the scope of the technical solution of the present invention.

Claims

1. A positive electrode active material comprising secondary particles composed of primary particles, the number σ of the primary particles in a unit spherical surface area in an SEM spectrum of the secondary particles being 5 pieces/μm²About 30 pieces/. mu.m²The single-particle compressive strength of the secondary particles is 60MPa to 300MPa,

the molecular formula of the positive active material is Li_xNi_yCo_zM_kMe_pO_rA_mX is more than or equal to 0.95 and less than or equal to 1.05, Y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, k is more than or equal to 0 and less than or equal to 1, r is more than or equal to 2, M is more than or equal to 0 and less than or equal to 2, M + r is less than or equal to 2, M is selected from Mn and/or Al, Me is selected from one or more combinations of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W and Nb, and A is selected from one or more combinations of N, F, S, Cl.

2. The positive electrode active material according to claim 1, wherein in the formula of the positive electrode active material, y is 0.70. ltoreq. y.ltoreq.0.95, z is 0. ltoreq. z.ltoreq.0.2, k is 0. ltoreq. k.ltoreq.0.2, and p is 0. ltoreq. p.ltoreq.0.05.

3. The positive electrode active material according to claim 1, wherein the powder compacted density of the positive electrode active material is not less than 3.3g/cm³。

4. The positive electrode active material according to claim 1, wherein D of the secondary particles_v10 is 2 to 8 μm, D_v50 is 5 to 18 μm, D_v90 is 10 to 30 μm.

5. The positive electrode active material according to claim 4, wherein the secondary particles are primary particles stacked in an extending direction of the primary particles, the primary particles have a rod shape, a cone shape, or a needle shape, the primary particles have a length of 100nm to 1000nm, the primary particles have a radial cross-sectional width of 50nm to 400nm, and preferably, a ratio of the length of the primary particles to the radial cross-sectional width is 2 to 10.

6. The positive electrode active material according to claim 1, wherein the secondary particles have a BET of 0.3m²/g～0.8m²/g。

7. The positive electrode active material according to claim 1, wherein at least a part of the primary particle surfaces at non-outermost positions in the secondary particles are provided with an inner coating layer comprising a coating element selected from one or more combinations of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P.

8. A positive electrode material, comprising the positive electrode active material as claimed in any one of claims 1 to 7, wherein an outer cladding layer is arranged on the surface of the positive electrode active material, the outer cladding layer comprises a cladding element, and the cladding element of the outer cladding layer is selected from one or more of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B and P.

9. The positive electrode material according to claim 8, wherein the outer clad layer is a continuous and/or discontinuous clad layer; preferably, the outer cladding layer is a composite form of a continuous first cladding layer and a non-continuous second cladding layer; more preferably, the substance of the discontinuous coating layer is different from the substance of the continuous coating layer.

10. A method for determining the number of primary particles per unit sphere surface area of the secondary particles in the positive electrode active material according to any one of claims 1 to 7 or the positive electrode material according to any one of claims 8 to 9, comprising the steps of:

σ＝(x1+x2)/2*(y1+y2)/2/(A/C*B/C)

wherein the content of the first and second substances,

11. An electrochemical energy storage device comprising the positive electrode active material according to any one of claims 1 to 7 or the positive electrode material according to any one of claims 8 to 9.