CN116014118A - High volume resistivity positive electrode material and preparation method thereof, lithium ion battery - Google Patents

Abstract

The invention relates to the field of lithium ion batteries, and discloses a high-volume-resistivity positive electrode material, a preparation method thereof and a lithium ion battery. The positive electrode material has a powder volume resistivity of 1,000-500,000Ω·cm. Compared with the traditional positive electrode material for the lithium ion battery, the positive electrode material has high powder volume resistivity performance, and when the positive electrode material is used for the lithium ion battery, the lithium ion battery has high discharge gram capacity, excellent high-temperature cycle performance and storage performance, so that the battery has improved safety.

Description

High volume resistivity positive electrode material and preparation method thereof, and lithium ion battery

Technical Field

The present invention relates to the field of lithium ion batteries, and in particular to a high volume resistivity positive electrode material and a preparation method thereof, and a lithium ion battery.

Background Art

Lithium-ion batteries are increasingly used in modern society. They are currently mainly used in mobile phones, laptops, power tools, electric vehicles and other fields. In recent years, with the increasing demand for large-capacity lithium-ion batteries, there is an urgent need to develop lithium-ion batteries with high energy density, high power, high safety, long life and more environmental protection. However, as the energy density of positive electrode materials continues to increase, their cycle performance and safety performance have declined. How to improve their cycle performance and safety performance without sacrificing capacity has become an urgent problem to be solved.

During repeated charge/discharge processes, the positive electrode material will undergo a phase change in the crystal structure accompanied by a change in volume, causing local collapse of the crystal layer structure, hindering the insertion/extraction of lithium ions, increasing the polarization resistance, and causing a decrease in the charge/discharge cycle performance.

On the other hand, when the positive electrode material is stored or cycled at high temperatures, gas will be generated, causing the battery to swell. This not only deteriorates the battery safety, but also causes the battery capacity retention rate to decay faster, seriously affecting the battery life.

The prior art attempts to solve the above problems by optimizing the synthesis conditions of the positive electrode materials, but the improvement effect is limited.

Summary of the invention

The purpose of the present invention is to overcome the problem that the capacity, cycle performance and safety of lithium-ion batteries in the prior art cannot be improved at the same time, and to provide a high volume resistivity positive electrode material and a preparation method thereof, and a lithium-ion battery. Compared with traditional positive electrode materials for lithium-ion batteries, the positive electrode material has a high powder volume resistivity performance, and when it is used in a lithium-ion battery, the lithium-ion battery has a higher discharge gram capacity, and has excellent high-temperature cycle performance and storage performance, so that the battery has improved safety.

In order to achieve the above object, the first aspect of the present invention provides a high volume resistivity positive electrode material, characterized in that the powder volume resistivity of the positive electrode material is 1,000-500,000 Ω·cm.

A second aspect of the present invention provides a method for preparing a high volume resistivity positive electrode material, characterized in that the preparation method comprises:

(1) mixing a positive electrode material precursor, a lithium source and an optional dopant to obtain a premix;

(2) sintering the premix in a first oxygen-containing atmosphere to obtain a primary sintered material;

(3) mixing the primary sintered material with the coating agent, and then performing a heat treatment in a second oxygen-containing atmosphere to obtain the high volume resistivity positive electrode material;

Wherein, the heat treatment conditions are: heat treatment temperature is 300-600°C, and heat treatment time is 1-12h.

The third aspect of the present invention provides a high volume resistivity positive electrode material prepared by the above preparation method.

A fourth aspect of the present invention provides a lithium-ion battery, characterized in that the lithium-ion battery comprises the above-mentioned high volume resistivity positive electrode material.

Through the above technical solution, the high volume resistivity positive electrode material and preparation method thereof, and the lithium ion battery provided by the present invention achieve the following beneficial effects:

The high volume resistivity positive electrode material provided by the present invention has a high powder volume resistivity. Furthermore, the positive electrode material has a high specific surface area, a large angle of repose and a high Li ₂ CO ₃ /LiOH content ratio. When the positive electrode material is used in a lithium ion battery, it can not only enable the lithium ion battery to maintain a high discharge gram capacity, but also significantly improve the cycle capacity retention rate and high-temperature storage performance of the lithium ion battery, thereby overcoming the difficult problem of significantly sacrificing the capacity of the lithium ion battery when improving the cycle life and high-temperature storage performance of the lithium ion battery, and achieving a balance between the cycle life, high-temperature storage performance and capacity of the lithium ion battery.

In the preparation method of the high volume resistivity positive electrode material provided by the present invention, the coating agent is coated on the positive electrode material substrate by low-temperature heat treatment, so that better coverage is formed on the surface of the positive electrode material, and the generation of the CEI film between the electrolyte and the positive electrode material is slowed down. The positive electrode material has poor electronic conductivity and high volume resistivity. At the same time, a Li ⁺ ion fast channel is constructed on the surface of the material to achieve rapid embedding and de-embedding of Li ⁺ ions inside and on the surface of the material, thereby improving the transmission efficiency of Li ⁺ ions, enhancing the kinetic characteristics of the material, and significantly improving the discharge gram capacity of the lithium ion battery containing the positive electrode material.

Furthermore, by using a specific coating agent and a low-temperature heat treatment process, the prepared positive electrode material has both a higher Li ₂ CO ₃ /LiOH content ratio and a high powder volume resistivity, which can not only improve the slurry processing performance of the positive electrode material, but also delay the thermal runaway process of the positive electrode material, so that the capacity retention rate of the lithium-ion battery containing the positive electrode material during high-temperature storage can be greatly improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a SEM electron microscope image of the positive electrode material A1 obtained in Example 1;

FIG. 2 is a SEM electron microscope image of the positive electrode material D1 prepared in Comparative Example 1.

DETAILED DESCRIPTION

The endpoints and any values of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, the endpoint values of each range and the individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

A first aspect of the present invention provides a high volume resistivity positive electrode material, characterized in that the powder volume resistivity of the positive electrode material is 1,000-500,000 Ω·cm.

The high volume resistivity positive electrode material provided by the present invention has a high powder volume resistivity. When the positive electrode material is used in a lithium ion battery, it can not only enable the lithium ion battery to maintain a high discharge gram capacity, but also significantly improve the high temperature capacity retention rate and high temperature storage performance of the lithium ion battery, thereby overcoming the difficult problem of significantly sacrificing the capacity of the lithium ion battery when improving the cycle life and high temperature storage performance of the lithium ion battery, and achieving a balance between the cycle life, high temperature storage performance and capacity of the lithium ion battery.

Furthermore, the powder volume resistivity of the positive electrode material is 1,500-30,000 Ω·cm.

According to the present invention, the specific surface area of the positive electrode material is 0.65-1.2 ^{m 2} /g, preferably 0.65-0.99 ^{m 2} /g.

According to the present invention, the repose angle of the positive electrode material is 45°-75°, preferably 50°-65°.

According to the present invention, the content ratio of Li ₂ CO ₃ on the surface of the positive electrode material to LiOH on the surface is 2-30.

In the present invention, when the content ratio of surface _Li2CO3 to surface _LiOH of the positive electrode material is controlled to meet the above range, the positive electrode material can have a high powder volume resistivity, thereby enabling the lithium ion battery containing the positive electrode material to maintain a high discharge gram capacity, and significantly improving the high temperature capacity retention rate and high temperature storage performance of the lithium ion battery.

Furthermore, the content ratio of Li ₂ CO ₃ on the surface of the positive electrode material to LiOH on the surface is 3-20.

In the present invention, when at least one of the powder volume resistivity, specific surface area, angle of repose and Li ₂ CO ₃ /LiOH content ratio of the positive electrode material meets the range defined in the present invention, the discharge gram capacity, high temperature capacity retention rate and high temperature storage performance of the lithium ion battery containing the positive electrode material can be improved, achieving a balance between the cycle life, high temperature storage performance and capacity of the lithium ion battery.

Furthermore, when the powder volume resistivity, specific surface area and Li ₂ CO ₃ /LiOH content ratio of the positive electrode material simultaneously meet the ranges defined in the present invention, the comprehensive performance of the lithium ion battery containing the positive electrode material can be further improved.

According to the present invention, the D ₅₀ of the positive electrode material is 2-10 μm, preferably 2.5-5.5 μm.

According to the present invention, the positive electrode material has a composition shown in Formula I:

Li _1+a (Ni _x Co _y Mn _z L _m )M _j O _2Formula I;

Among them, -0.1≤a≤0.1, 0＜x＜1, 0＜y≤0.4, 0＜z≤0.6, 0≤m≤0.1, 0＜j≤0.02;

L is at least one element selected from the group consisting of Cr, Fe, Mg, Ca, Sr, Ba, B, Al, Y, Sm, Ti, Zn, Zr, Hf, V, Nb, Ta, Mo, W and Ce;

M is at least one element selected from Mg, Sr, Ba, Zr, B, Al, Y, V, Nb, Ta, Mo, W, Ti, Co and Ce.

In the present invention, in the above-mentioned positive electrode material, L is introduced by the dopant in the preparation process, and M is introduced by the coating agent.

Further, 0≤a≤0.06, 0.3＜x＜0.9, 0＜y≤0.2, 0＜z≤0.1, 0≤m≤0.01, 0.0005≤j≤0.01.

Furthermore, L is at least one element selected from Mg, Ca, Sr, Ba, B, Al, Y, Ti, Zr and W.

Furthermore, M is at least one element selected from Mg, Ba, Al, Y, W, Ti and Co.

Furthermore, L and M are different.

In a preferred embodiment of the present invention, L is at least one element selected from Mg, Sr, Y and Zr.

In a preferred embodiment of the present invention, M is at least one element selected from the group consisting of Ba, B, Al, W, Ti and Ce.

A second aspect of the present invention provides a method for preparing a high volume resistivity positive electrode material, characterized in that the preparation method comprises the following steps:

(1) mixing a positive electrode material precursor, a lithium source and an optional dopant to obtain a premix;

(2) sintering the premix in a first oxygen-containing atmosphere to obtain a primary sintered material;

(3) mixing the primary sintered material with the coating agent, and then performing a heat treatment in a second oxygen-containing atmosphere to obtain the high volume resistivity positive electrode material;

Wherein, the heat treatment conditions are: heat treatment temperature is 300-600°C, and heat treatment time is 1-12h.

In the present invention, in the preparation method, the coating agent is coated on the positive electrode material substrate by low-temperature heat treatment, so that a better coverage is formed on the surface of the positive electrode material, and the generation of the CEI film between the electrolyte and the positive electrode material is slowed down. The positive electrode material has poor electronic conductivity and high volume resistivity. At the same time, a Li ⁺ ion fast channel is constructed on the surface of the material to achieve rapid embedding and de-embedding of Li ⁺ ions inside and on the surface of the material, thereby improving the transmission efficiency of Li ⁺ ions, enhancing the kinetic characteristics of the material, and significantly improving the discharge gram capacity of the lithium ion battery containing the positive electrode material.

In the present invention, preferably, a doped and modified positive electrode material is used as a substrate. The coating layer formed after the substrate is coated with a coating agent under low-temperature heat treatment conditions effectively reduces the side effects between the surface of the positive electrode material and the electrolyte. Since the coating layer has good spreadability, it can form a better coverage on the surface of the substrate, further preventing the generation of a CEI film between the electrolyte and the positive electrode material, resulting in poor electronic conductivity of the positive electrode material and high volume resistivity. At the same time, the coating layer reacts moderately with the residual lithium on the surface of the positive electrode material to form a multivalent compound, construct a Li ⁺ fast channel, and realize the rapid release and embedding of Li ⁺ ions inside and on the surface of the material, which significantly improves the discharge gram capacity of the material; since the heat treatment temperature is low during the coating process, the crystal structure of the surface layer of the substrate is not damaged, the coating layer effectively covers the surface of the material substrate and improves the surface and interface structure stability of the positive electrode material, thereby significantly improving the cycle life and high-temperature storage performance of the lithium-ion battery containing the positive electrode material.

Furthermore, by using a specific coating agent and a low-temperature heat treatment process, the prepared positive electrode material has both a higher Li ₂ CO ₃ /LiOH content ratio and a high powder volume resistivity, which can not only improve the slurry processing performance of the positive electrode material, but also delay the thermal runaway process of the positive electrode material, so that the capacity retention rate of the lithium-ion battery containing the positive electrode material during high-temperature storage can be greatly improved.

Furthermore, the heat treatment conditions include: the heat treatment temperature is 350-500° C., and the heat treatment time is 4-12 hours.

According to the present invention, the cathode material precursor is a nickel-cobalt-manganese composite compound.

According to the present invention, the cathode material precursor has a composition shown in Formula II:

Ni _x Co _y Mn _z (OH) ₂ Formula II;

Among them, 0＜x＜1, 0＜y≤0.4, 0＜z≤0.6.

Furthermore, 0.3＜x＜0.9, 0＜y≤0.2, 0＜z≤0.1.

According to the present invention, the D ₅₀ of the cathode material precursor is 2-10 μm, preferably 2.5-5.5 μm.

According to the present invention, the lithium source is selected from at least one of lithium carbonate, lithium nitrate and lithium hydroxide.

According to the present invention, the average particle size of the lithium source is 2-20 μm.

According to the present invention, the dopant is selected from at least one of oxides, oxyhydroxides, hydroxides, carbonates and oxalates containing the L element.

Furthermore, the L element is selected from at least one element of Cr, Fe, Mg, Ca, Sr, Ba, B, Al, Y, Sm, Ti, Zn, Zr, Hf, V, Nb, Ta, Mo, W and Ce.

According to the present invention, the amounts of the lithium source and the cathode material precursor are such that 0.9≤n(Li)/[n(Ni)+n(Co)+n(Mn)]≤1.1.

Furthermore, the amounts of the lithium source and the positive electrode material precursor are such that 1≤n(Li)/[n(Ni)+n(Co)+n(Mn)]≤1.06.

According to the present invention, the amounts of the dopant and the cathode material precursor are such that 0≤n(L)/[n(Ni)+n(Co)+n(Mn)]≤0.1.

Furthermore, the dosage of the dopant and the positive electrode material precursor is such that 0≤n(L)/[n(Ni)+n(Co)+n(Mn)]≤0.01.

According to the present invention, the content of oxygen in the first oxygen-containing atmosphere is ≥50 vol%, and the dew point of the first oxygen-containing atmosphere is ≤-10°C.

In the present invention, the sintering is carried out in the first oxygen-containing atmosphere having the above-mentioned oxygen content and dew point, the nickel-lithium mixed arrangement in the positive electrode material is smaller, the single crystal growth is more perfect, the lattice defects are fewer, and the residual alkali in the positive electrode material after sintering is lower, thereby enabling the lithium-ion battery containing the positive electrode material to have better cycle performance.

Furthermore, the oxygen content in the first oxygen-containing atmosphere is 70-100 vol%, and the dew point of the first oxygen-containing atmosphere is ≤-20°C.

In the present invention, the first oxygen-containing atmosphere is pure oxygen or a mixture of oxygen and air.

According to the present invention, the dew point of the second oxygen-containing atmosphere is ≤ -10°C, preferably ≤ -20°C.

In the present invention, when the dew point of the second oxygen-containing atmosphere is controlled to meet the above range during the heat treatment process, the residual alkali is not easily converted during the heat treatment process, and the structural lithium is not easily precipitated, thereby maintaining the internal and surface structural stability of the material to the greatest extent, so that the electrical properties of the positive electrode material obtained thereby can be better exerted.

In the present invention, there is no particular limitation on the oxygen content in the second oxygen-containing atmosphere, and an oxygen-containing atmosphere with a conventional oxygen content in the art may be used, for example, the oxygen content in the second oxygen-containing atmosphere is ≥ 21 vol%. In the present invention, the second oxygen-containing atmosphere is air.

In the present invention, the oxygen content in the second oxygen-containing atmosphere is less than the oxygen content in the first oxygen-containing atmosphere.

According to the present invention, the amount of the first oxygen-containing atmosphere introduced is 2-40 m ³ /kg·h relative to the weight of the premix.

In the present invention, when the amount of the first oxygen-containing atmosphere introduced during the sintering process is controlled to meet the above range, the sintering process is sufficient, which can promote the perfection of the crystal form. The surface residual alkali of the positive electrode material thus obtained is low, and the electrical properties of the positive electrode material can be better exerted.

Furthermore, relative to the weight of the premix, the amount of the first oxygen-containing atmosphere introduced is 3-20 m ³ /kg·h.

According to the present invention, the sintering conditions include: a sintering temperature of 800-1100° C. and a sintering time of 5-20 hours.

Furthermore, the sintering conditions include: a sintering temperature of 900-990° C. and a sintering time of 8-20 hours.

In the present invention, there is no particular limitation on the amount of the second oxygen-containing atmosphere introduced. For example, relative to the weight of the primary sintering material, the amount of the second oxygen-containing atmosphere introduced may be 0.5-5 m ³ /kg·h.

According to the present invention, the coating agent is selected from at least one of oxides, oxyhydroxides, hydroxides, carbonates, sulfates and borates containing the M element.

Furthermore, the M element is selected from at least one element of Mg, Sr, Ba, Zr, B, Al, Y, V, Nb, Ta, Mo, W, Ti, Co and Ce.

In a specific embodiment of the present invention, the coating agent includes but is not limited to: at least one of Al ₂ O ₃ , ZrO ₂ , MgO, TiO ₂ , Nb ₂ O ₅ , ZnO, CaO, B ₂ O ₃ , Y ₂ O ₃ , SiO ₂ , AlOOH, CoOOH, WO ₃ , CeO ₂ , Al(OH) ₃ , ZrO(OH) ₂ , Sr(OH) ₂ , Mg(OH) ₂ , Ti(OH) ₄ , Zn(OH) ₂ , Ca(OH) ₂ , Co(OH) ₂ , MgCO ₃ , BaCO ₃ , SrCO ₃ , BaSO ₄ , and H ₃ BO ₃ .

According to the present invention, the amounts of the coating agent and the primary sintering material are such that 0＜n(M)/[n(Ni)+n(Co)+n(Mn)]≤0.02.

In the present invention, when the amounts of the coating agent and the primary sintering material are controlled to meet the above ranges, the prepared positive electrode material can have a high Li ₂ CO ₃ /LiOH content ratio and a high powder volume resistivity, thereby making the lithium ion battery containing the positive electrode material have a high material discharge gram capacity, and a high high temperature capacity retention rate and high temperature storage performance.

Furthermore, the coating agent and the primary sintering material are used in an amount such that 0.0005≤n(M)/[n(Ni)+n(Co)+n(Mn)]≤0.01.

The third aspect of the present invention provides a high volume resistivity positive electrode material prepared by the above preparation method.

A fourth aspect of the present invention provides a lithium-ion battery, characterized in that the lithium-ion battery comprises the above-mentioned high volume resistivity positive electrode material.

The present invention will be described in detail below by way of examples. In the following examples,

The powder volume resistivity of the cathode material was measured using a Mitsubishi Chemical MCP-PD51 powder resistance meter under a pressure of 20 kN;

The average particle size of the cathode material precursor, cathode material D ₅₀ , and lithium source was measured using a laser particle size analyzer of the Hydro 2000mu model from Marvern.

The specific surface area of the positive electrode material was measured using a Tristar 3020 surface area analyzer from Micromeritics.

The repose angle of the positive electrode material was measured using the Hosokawa comprehensive powder tester-fluidity and jetting tester (PT-X);

The surface Li ₂ CO ₃ content and surface LiOH content of the positive electrode material were measured using a Wantong "Mystery" type potentiometric titrator;

The composition of cathode material precursor and cathode material was measured by ICP-OES/PE Avio 200 potentiometric titrator;

The discharge capacity and cycle performance of lithium-ion batteries were measured using 2025 button cells.

The assembly method of lithium-ion battery (button battery) includes:

Preparation of pole piece: The positive electrode material, acetylene black and polyvinylidene fluoride (PVDF) were mixed with an appropriate amount of N-methylpyrrolidone (NMP) in a mass ratio of 95:3:2 to form a uniform slurry. The slurry was coated on aluminum foil and dried at 120°C for 12 hours. It was then stamped at a pressure of 100 MPa to form a positive pole piece with a diameter of 12 mm and a thickness of 120 μm. The loading amount of the positive electrode material was 15-16 mg/cm ² .

Battery assembly: In an argon-filled glove box with a water content and oxygen content of less than 5ppm, the positive electrode, separator, negative electrode and electrolyte were assembled into a 2025 button cell and left to stand for 6 hours. The negative electrode used a metal lithium sheet with a diameter of 17mm and a thickness of 1mm; the separator used a polyethylene porous membrane (Celgard 2325) with a thickness of 25μm; and the electrolyte used an equal mixture of 1mol/L LiPF ₆ , ethylene carbonate (EC) and diethyl carbonate (DEC).

Electrochemical performance test:

In the following examples and comparative examples, the electrochemical performance of 2025 button batteries was tested using Shenzhen Xinwell battery testing system.

The charge and discharge voltage range was controlled to be 3.0-4.4V. At room temperature, the button cell was charged and discharged at 0.1C to evaluate the initial charge and discharge specific capacity and initial charge and discharge efficiency of the lithium-ion battery.

Cycle performance test: Control the charge and discharge voltage range to 3.0-4.4V. At a constant temperature of 45°C, charge and discharge the button battery twice at 0.1C, and then charge and discharge 50 times at 1C to evaluate the high-temperature capacity retention rate of the lithium-ion battery.

The high temperature storage performance of lithium-ion batteries was measured using stacked full cells.

The assembly method of lithium-ion battery (full battery) includes:

Preparation of positive electrode sheet: The multi-element positive electrode material, SP, CNT and polyvinylidene fluoride (PVDF) were fully mixed with an appropriate amount of N-methylpyrrolidone (NMP) in a mass ratio of 96.7:1:0.8:1.5 to form a uniform slurry, and the slurry was coated on aluminum foil. After the drying process, a die-cutting machine was used to punch out 112mm×40mm electrode sheets, in which the positive electrode material loading was 370g/ ^m2 ;

Preparation of negative electrode sheet: The negative electrode material, SP, CMC, and SBR were mixed with an appropriate amount of pure water in a mass ratio of 96.5:0.5:1.2:1.8 to form a uniform slurry, and the slurry was coated on a copper foil. After a drying process, a die-cutting machine was used to punch out 115 mm × 41.5 mm electrode sheets, wherein the loading amount of the negative electrode material was 222 g/m ² .

Battery assembly: Z-shaped stacking is carried out in an environment with a dew point of -40°C. The positive and negative electrodes correspond to each other and are separated by a diaphragm. After the battery cell is assembled, it is vacuum baked at 85°C.

Liquid injection: Inject 7.5 ml of liquid into the assembled battery cell in the glove box and soak it at 45°C for 24 hours.

Electrochemical performance test: The battery is pre-charged and discharged with a small current using a clamp. The battery is sealed for the second time to remove the air bag and then put on the cabinet for 0.2C, 0.33C, 0.5C, and 1C charging and discharging to complete the battery capacity separation.

70℃/30 days high temperature storage capacity retention test: The fully charged batteries were placed in a 70℃ high temperature blast oven for 4, 8, 12, 20 and 30 days respectively. The batteries were taken out each time for capacity retention and recovery tests.

Example 1

(1) The positive electrode material precursor Ni _0.6 Co _0.1 Mn _0.3 (OH) ₂ (D ₅₀ is 3.3 μm) is fully mixed with Li ₂ CO ₃ (average particle size is 6 μm), ZrO ₂ and SrCO ₃ in a molar ratio of n(Li):[n(Ni)+n(Co)+n(Mn)]:n(Zr):n(Sr)=1.05:1:0.003:0.002 to obtain a premix.

(2) After premixing, the mixed material was sintered at 975°C for 20h in a first oxygen-containing atmosphere (oxygen content of 90 vol%, dew point of -25°C, flow rate of ^10m3 /kg·h) to obtain a primary sintered material, which was crushed to obtain an intermediate product.

(3) The intermediate product was fully mixed with coating agents TiO ₂ and WO ₃ according to the molar ratio of [n(Ni)+n(Co)+n(Mn)]:n(Ti):n(W)=1:0.002:0.003 by dry method, and then heat treated in a second oxygen-containing atmosphere (oxygen content was 21 vol%, dew point was -25°C, and the flow rate was 1.5 m ³ /kg·h). The heat treatment temperature was controlled at 400°C and the heat treatment time was 12 hours. After the heat treatment was completed, the material was cooled and sieved to obtain a high volume resistivity positive electrode material A1.

Example 2-18

According to the method of Example 1, a high volume resistivity positive electrode material was prepared, and the raw material ratio and specific process conditions are shown in Table 1. Positive electrode materials A2-A18 were prepared.

Comparative Examples 1-4

The positive electrode material was prepared according to the method of Example 1, and the raw material ratio and specific process conditions are shown in Table 1. Positive electrode materials D1-D4 were prepared.

Table 1

Table 1 (continued)

Table 1 (continued)

Table 1 (continued)

Table 1 (continued)

Table 1 (continued)

Table 1 (continued)

The compositions of the positive electrode materials prepared in the examples and comparative examples are shown in Table 2.

Table 2

The BET, Li ₂ CO ₃ /LiOH ratio, repose angle, powder volume resistivity and D ₅₀ of the positive electrode materials of the embodiment and the comparative example were tested. The results are shown in Table 3.

Table 3

BET/ ^m2 /g Li ₂ CO ₃ /LiOH Angle of repose/° Powder volume resistivity/Ω·cm D50 _/ μm Example 1 0.82 5.4 56.9 4550 3.7 Example 2 0.72 3 58.5 22650 3.7 Example 3 0.99 20 59.7 3860 3.7 Example 4 0.92 25 58.7 5510 3.8 Example 5 0.85 8.1 56.7 28550 3.7 Example 6 0.95 18.5 56.7 65590 3.6 Example 7 0.65 5.1 52.5 1620 3.6 Example 8 0.84 4.8 54.8 4320 3.7 Example 9 0.80 5.8 56.7 3420 3.7 Example 10 0.83 4.9 57.9 5840 3.7 Embodiment 11 0.88 6.2 50.2 10550 3.7 Example 12 0.86 8.3 57.1 4060 3.8 Example 13 0.77 5 56.4 3112 3.7 Embodiment 14 0.88 12.2 63.5 25640 3.6 Embodiment 15 0.66 3.1 52.4 12880 3.6 Example 16 0.78 5.1 55.7 5540 3.6 Embodiment 17 0.82 4.3 56.5 6530 3.7 Embodiment 18 0.80 1.5 50.5 855 3.7 Comparative Example 1 0.58 1.9 48.2 799 3.8 Comparative Example 2 0.59 1.2 46.1 506 3.8 Comparative Example 3 0.56 0.9 44.6 655 3.8 Comparative Example 4 0.58 0.8 47.6 457 3.7

The positive electrode materials prepared in the examples and comparative examples were assembled into lithium ion batteries, and the electrochemical performance of the lithium ion batteries was tested. The results are shown in Table 4.

Table 4

It can be seen from Tables 3 and 4 that the lithium ion battery prepared using the positive electrode material of the present invention having high BET, large repose angle, high Li ₂ CO ₃ /LiOH content ratio and high powder volume resistivity not only has a high initial discharge capacity, but also has a high capacity retention rate and high temperature storage capacity retention rate.

FIG1 is a SEM electron microscope image of the positive electrode material A1 prepared in Example 1. It can be seen from FIG1 that the particles on the surface of the material are distributed in an "island" shape; FIG2 is a SEM electron microscope image of the positive electrode material D1 prepared in Example 1. It can be seen from FIG2 that the particles on the surface of the material are distributed in a "fine dot" shape.

Claims (10)

1. A high volume resistivity positive electrode material, characterized in that the powder volume resistivity of the positive electrode material is 1,000-500,000 Ω -cm.

2. The high volume resistivity positive electrode material of claim 1, wherein the positive electrode material has a powder volume resistivity of 1,500-30,000 Ω -cm;

preferably, D of the positive electrode material ₅₀ 2-10 μm, preferably 2.5-5.5 μm;

preferably, the specific surface area of the positive electrode material is 0.65-1.2m ² Preferably 0.65-0.99m ² /g；

Preferably, the angle of repose of the positive electrode material is 45 ° -75 °, preferably 50 ° -65 °;

preferably, the surface Li of the positive electrode material ₂ CO ₃ The ratio to the surface LiOH content is 2 to 30, preferably 3 to 20.

3. The high volume resistivity positive electrode material of claim 1 or 2, wherein the positive electrode material has a composition represented by formula I:

Li _1+a (Ni _x Co _y Mn _z L _m )M _j O ₂ a formula I;

wherein, -0.1 is more than or equal to a and less than or equal to 0.1, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 0.4, z is more than or equal to 0 and less than or equal to 0.6,0, m is more than or equal to 0.1, and j is more than or equal to 0 and less than or equal to 0.02;

l is at least one element selected from Cr, fe, mg, ca, sr, ba, B, al, Y, sm, ti, zn, zr, hf, V, nb, ta, mo, W and Ce;

m is at least one element selected from Mg, sr, ba, zr, B, al, Y, V, nb, ta, mo, W, ti, co and Ce;

preferably, a is more than or equal to 0 and less than or equal to 0.06,0.3, x is more than or equal to 0.9, y is more than or equal to 0 and less than or equal to 0.2, z is more than or equal to 0 and less than or equal to 0.1, m is more than or equal to 0 and less than or equal to 0.01,0.0005 and j is more than or equal to 0 and less than or equal to 0.01;

preferably, L is selected from at least one element of Mg, ca, sr, ba, B, al, Y, ti, zr and W;

preferably, M is at least one element selected from Mg, ba, al, Y, W, ti and Co;

preferably, L and M are different.

4. A method for preparing a high volume resistivity positive electrode material, the method comprising:

(1) Mixing a positive electrode material precursor, a lithium source and optionally a dopant to obtain a premix;

(2) Sintering the premix in a first oxygen-containing atmosphere to obtain a primary sintered material;

(3) Mixing the primary sintering material with a coating agent, and then performing heat treatment in a second oxygen-containing atmosphere to obtain the high-volume-resistivity anode material;

wherein the conditions of the heat treatment include: the heat treatment temperature is 300-600 ℃, and the heat treatment time is 1-12h.

5. The production method according to claim 4, wherein the conditions of the heat treatment include: the heat treatment temperature is 350-500 ℃, and the heat treatment time is 4-12h.

6. The production method according to claim 4 or 5, wherein the positive electrode material precursor is a nickel-cobalt-manganese composite compound;

preferably, the positive electrode material precursor has a composition represented by formula II:

Ni _x Co _y Mn _z (OH) ₂ a formula II;

wherein x is more than 0 and less than 1, y is more than 0 and less than or equal to 0.4, and z is more than 0 and less than or equal to 0.6;

preferably, D of the positive electrode material precursor ₅₀ 2-10 μm, preferably 2.5-5.5 μm;

preferably, the lithium source is selected from at least one of lithium carbonate, lithium nitrate and lithium hydroxide;

preferably, the average particle size of the lithium source is 2-20 μm;

preferably, the dopant is selected from at least one of an oxide, a oxyhydroxide, a hydroxide, a carbonate, and an oxalate containing an L element;

more preferably, the L element is at least one element selected from Cr, fe, mg, ca, sr, ba, B, al, Y, sm, ti, zn, zr, hf, V, nb, ta, mo, W and Ce;

preferably, the lithium source and the positive electrode material precursor are used in such an amount that 0.9.ltoreq.n (Li)/[ n (Ni) +n (Co) +n (Mn) ].ltoreq.1.1;

preferably, the dopant is used in an amount such that 0.ltoreq.n (L)/[ n (Ni) +n (Co) +n (Mn) ] is.ltoreq.0.1 with the positive electrode material precursor.

7. The production method according to any one of claims 4 to 6, wherein the content of oxygen in the first oxygen-containing atmosphere is 50 vol.% or more, and the dew point of the first oxygen-containing atmosphere is 10 ℃ or less;

preferably, the dew point of the second oxygen-containing atmosphere is less than or equal to-10 ℃;

preferably, the first oxygen-containing atmosphere is introduced in an amount of from 2 to 40m, relative to the weight of the premix ³ /kg·h；

Preferably, the sintering conditions include: the sintering temperature is 800-1100 ℃ and the sintering time is 5-20h.

8. The production method according to any one of claims 4 to 7, wherein the coating agent is at least one selected from the group consisting of an oxide, a oxyhydroxide, a hydroxide, a carbonate, a sulfate, and a borate containing an M element;

preferably, the M element is at least one element selected from Mg, sr, ba, zr, B, al, Y, V, nb, ta, mo, W, ti, co and Ce;

preferably, the usage of the cladding agent and the primary sintering material is 0 < n (M)/[ n (Ni) +n (Co) +n (Mn) ] < 0.02.

9. A high volume resistivity positive electrode material made by the method of any one of claims 4-8.

10. A lithium ion battery comprising the high volume resistivity positive electrode material of any one of claims 1-3 and 9.

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