Multi-element positive electrode material and preparation method therefor, positive electrode sheet, and lithium ion battery

Abstract

A multi-element positive electrode material and a preparation method therefor, and a positive electrode sheet and a lithium ion battery using the multi-element positive electrode material. The multi-element positive electrode material is secondary particles formed by agglomerating primary particles, wherein the ratio of the total cross-sectional area of the primary particles having five or more grain boundaries to the cross-sectional area of the secondary particles is greater than or equal to 3:4; the porosity of the cross section of the secondary particles is less than or equal to 2%; each grain boundary is the contour line of an interface between the primary particles with the same structure and different orientations on the cross section of the secondary particles, and the length of the grain boundary is greater than or equal to 0.1 μm. The internal crystal grains of the multi-element positive electrode material are irregularly, non-radially and disorderly arranged, so that the multi-element positive electrode material has high powder compaction density and processing performance. Moreover, the positive electrode sheet containing the multi-element positive electrode material easily bears high rolling pressure, and does not easily break.

Description

Multi-element positive electrode material and preparation method thereof, positive electrode sheet, and lithium-ion battery

[0001] Priority information

[0002] This application claims priority to and the benefits of patent application 202311394203.9 filed on October 25, 2023 with the State Intellectual Property Office of China, and incorporates the entire text of that application herein by reference. Technical Field

[0003] The present invention relates to the technical field of lithium-ion batteries, and in particular to a multi-element positive electrode material and a preparation method thereof, a positive electrode sheet containing the multi-element positive electrode material, and a lithium-ion battery containing the positive electrode sheet. Background Art

[0004] Lithium-ion batteries are primarily classified into cylindrical, prismatic, and pouch-type batteries. From small consumer devices to power tools, power batteries, and even energy storage, lithium-ion batteries have a wide range of applications. Due to strong demand, their production has grown rapidly, and production technology has advanced by leaps and bounds.

[0005] The manufacturing process of lithium-ion batteries is relatively complicated, usually including steps such as slurrying, coating, rolling, cutting, injecting, and winding the positive electrode material. Therefore, it is very important that the positive electrode material can maintain sufficient stability during each manufacturing process. In the actual production process of lithium batteries, manufacturers often increase the amount of positive electrode material used or use greater pressure in the rolling process in order to pursue the energy density of lithium-ion batteries. However, excessive pressure can easily cause the positive electrode fragments to break, causing the electrode pieces to be scrapped and ultimately leading to a high battery defect rate. From the perspective of positive electrode material performance, the generation of electrode fragments is largely related to the structure of the positive electrode material itself.

[0006] Generally speaking, when designing positive electrode materials, to improve cycle performance, they are intentionally designed with a radially distributed cross-section. However, during the production of battery pole pieces, when high rolling pressure is used to achieve sufficient energy density, this type of positive electrode material will transfer the pressure radially to the aluminum foil pole piece coated with the positive electrode. The same pressure direction is amplified, which can easily lead to pole piece fracture, greatly reducing the defective rate of battery pole pieces. This phenomenon can also affect the battery's electrical performance, especially the battery's safety performance, high-temperature stability and cycle performance, and cannot meet the high safety requirements of electric vehicle batteries.

[0007] Summary of the Invention

[0008] The purpose of the present invention is to overcome the problems of existing battery pole pieces that are easy to break, cannot withstand high rolling pressure, and the batteries assembled therefrom have low safety performance, high temperature stability and cycle performance. The present invention provides a multi-element positive electrode material and its preparation method, a positive electrode pole piece and a lithium-ion battery. The internal grains of the multi-element positive electrode material are irregularly non-radially disordered, so that the multi-element positive electrode material has a higher powder compaction density and processing performance; at the same time, the positive electrode pole piece containing the multi-element positive electrode material can easily withstand high rolling pressure and is not prone to pole piece breakage.

[0009] To achieve the above objectives, the present invention provides, in a first aspect, a multi-element positive electrode material, wherein the multi-element positive electrode material is a secondary particle formed by agglomeration of primary particles, wherein the ratio of the total cross-sectional area of ​​the primary particles having 5 or more grain boundaries to the cross-sectional area of ​​the secondary particles is ≥3:4; and the porosity of the cross-sectional area of ​​the secondary particles is ≤2%.

[0010] The grain boundary refers to the outline of the interface between primary particles with the same structure but different orientations on the cross section of the secondary particle, and the length of the grain boundary is ≥0.1 μm.

[0011] In the present invention, unless otherwise specified, the cross section of the secondary particle refers to the cross section after ion milling, preferably refers to the cross section after ion milling with a cross-sectional diameter equal to the DB of the secondary particle. 50 cross-section of the particles.

[0012] In the present invention, the cross section of the secondary particles used to determine the number of grain boundaries is obtained as follows:

[0013] S1. Sample preparation: a. Cut 2×4cm 2 Aluminum foil and 1.5×1.5cm 2 a. Prepare silicon wafers of standard specifications, fold the aluminum foil in half, flatten both sides, and reserve a gap in the middle for placing the sample; b. Add conductive glue to the positive electrode material powder and mix evenly, then pick up the mixed material and place it in the reserved gap of the aforementioned aluminum foil, then place the aluminum foil on the platform, use a flat plate to compact the periphery of the sample first, and then gently press the middle of the sample to obtain a pretreated sample, mark the side of the pretreated sample that contacts the platform as the front side, and the pressed side as the back side; c. Dry the pretreated sample at 100°C for 60 minutes, take out the pretreated sample after drying, cut off the excess aluminum foil on the pretreated sample without sample, and then cut the sample vertically from the back side at a location with sufficient sample; d. Take the above-mentioned silicon wafer, use glue to stick the back side of the cut pretreated sample to the silicon wafer, so that the relatively flat front side of the sample can be close to the baffle and face the ion beam positively. When pasting, ensure that the cut surface of the aluminum foil protrudes from the edge of the silicon wafer or is flush with it, for example, protruding by more than 60μm, to obtain the sample to be tested.

[0014] S2. Measurement: Glue conductive tape on the side of the sample stage and fix the sample to be tested on the sample stage, wherein the upper edge of the sample to be tested should be about 1-3 mm higher than the sample stage. Then perform ion milling on the sample to be tested on the sample stage. After milling, apply liquid conductive glue in the gap between the silicon wafer and the sample to be tested to increase conductivity. Finally, place the treated sample stage on a sample stage holder dedicated to the electron microscope, fix the position of the sample stage with an inner hexagon, and obtain a cross-sectional sample by electron microscope observation. The ion milling instrument used in the present invention is the Hitachi ion milling instrument IM4000PLUS. Please refer to Table 1 for ion milling conditions:

[0015] Table 1

[0016] Among them, based on the ion milling profile obtained by the above method, the DB of the cross-sectional diameter and secondary particles were screened out. 50 Observe particles of equal size, as such cross-sections passing through or near the center of the sphere are more representative. When performing ion milling, the ion miller's STAGE CONT should be set to C4 mode, with a 40-minute operating time, an accelerating voltage of 6 kV, a maximum discharge voltage, and an airflow of 0.09 cm³ / min. Electron microscopy testing conditions were low-voltage backscatter mode, voltage = 1 kV, WD = 2.5 mm, and a magnification of 10k.

[0017] Preferably, the powder compaction density of the multi-element positive electrode material is ≥3.4 g / cm 3 .

[0018] Preferably, the total residual alkali content of the multi-element positive electrode material satisfies: m(Li2CO3)+m(LiOH)<6000ppm.

[0019] A second aspect of the present invention provides a method for preparing a multi-element positive electrode material, the method comprising the following steps:

[0020] (1) mixing a precursor having a composition represented by formula II and a lithium source to obtain a mixture I, wherein the precursor is formed by agglomeration of primary crystals, and the primary crystals on a cross section of the precursor are non-radially distributed;

[0021] (2) sintering the mixture I once in an oxygen-containing atmosphere to obtain a process product; the conditions of the primary sintering include: heating the mixture to T1 at a heating rate of V1 and maintaining the temperature at t1; then heating the mixture to T2 at a heating rate of V2 and maintaining the temperature at t2;

[0022] (3) mixing the in-process product and an optional coating agent containing G to obtain a mixture II;

[0023] (4) sintering the product or mixture II twice in an oxygen-containing atmosphere to obtain a multi-element positive electrode material;

[0024] Among them, (Ni α Co β Mn γ M δ )(OH)2(II), 0.3≤α<1, 0<β<0.5, 0<γ<0.5, 0≤δ≤0.05, and α+β+γ+δ=1; M and G are each independently selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, B, Al, Co and Y.

[0025] Preferably, the precursor is prepared by the following method: in an inert atmosphere, a mixed metal salt solution containing a nickel source, a cobalt source, a manganese source and an optional M-containing dopant is subjected to a co-precipitation reaction with a precipitant, a complexing agent and a dispersant, and the obtained co-precipitation reaction product is washed and dried in sequence to obtain the precursor.

[0026] Preferably, the coprecipitation reaction conditions include: a temperature selected from 40-80° C., a pH value of 10-13, and a stirring speed selected from 200-550 rpm.

[0027] Preferably, in step (2), the conditions for the primary sintering include:

[0028] The heating rate V1 is selected from 1-6°C / min, preferably from 1-3°C / min, more preferably from 1-2°C / min; T1 is selected from 400-760°C, preferably from 500-750°C; the holding time t1 is selected from 2-6h, preferably from 3-5h; the heating rate V2 is selected from 1-6°C / min, preferably from 1-3°C / min; T2 is selected from 710-950°C, preferably from 710-920°C; the holding time t2 is selected from 5-13h, preferably from 6-12h.

[0029] A third aspect of the present invention provides a positive electrode plate, wherein the active material layer of the positive electrode plate contains the multi-element positive electrode material provided by the first aspect, or the multi-element positive electrode material prepared by the preparation method provided by the second aspect.

[0030] A fourth aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the positive electrode sheet provided by the third aspect.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] (1) The multi-element positive electrode material provided by the present invention has a ratio of the total cross-sectional area of ​​the primary particles with more than 5 grain boundaries to the cross-sectional area of ​​the secondary particles of ≥3:4. The grain boundaries herein satisfy a length ≥0.1μm, and the porosity on the cross-sectional surface of the secondary particles is ≤2%. Therefore, most of the primary particles constituting the secondary particles are closely arranged and have a large number of grain boundaries. It can also be understood that on the cross-sectional surface of the secondary particles, most of the cross-sectional surfaces of the primary particles of the present invention are multi-angular. Based on the closely arranged characteristics of the multi-element positive electrode material with multi-angular cross-sections, the multi-element positive electrode material provided by the present invention can disperse and conduct the pressure received along the interfaces in multiple directions under extreme compaction, that is, the internal primary particles will creep under pressure and are not easily broken. When the multi-element positive electrode material with this structure is used for positive electrode plates, the fracture of the plates can be reduced, so that the multi-element positive electrode material has a higher powder compaction density and processing performance;

[0033] (2) The preparation method provided by the present invention uses a precursor with disordered internal grains and prepares a multi-element positive electrode material with the same disordered internal grains by optimizing a primary sintering process; specifically, the co-precipitation reaction conditions are controlled to maintain the disordered growth of the seed crystals, so that the primary grains are non-radially disordered and distributed, thereby preparing a precursor that meets the requirements; after the above-mentioned precursor is fully mixed with the lithium source, a double-platform heat preservation sintering process curve is used to allow the lithium source to slowly and fully react with the precursor, and the obtained process product is then coated to finally obtain a multi-element positive electrode material with fully grown grains and disordered grains;

[0034] (3) The multi-element positive electrode material provided by the present invention is used for positive electrode plates. When it contains a specific doping element M, the doping element M will be distributed at the interface and will be in an amorphous state. When squeezed, the specific doping element M can act as a lubricant, making the secondary particles less likely to break and only causing relative displacement, thereby slowing down the occurrence of plate fragmentation. At the same time, it also ensures that the electrical properties of the material are not affected and it is easy to withstand higher rolling pressure, and it is not easy to produce plate fragmentation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a SEM image of a cross section of the precursor S1 prepared in Preparation Example 1;

[0036] FIG2 is a SEM image of a cross section of the precursor DS1 prepared in Comparative Preparation Example 1;

[0037] FIG3 is a SEM image of a cross section of the multi-element cathode material P3 prepared in Example 3;

[0038] FIG4 is a SEM image of a cross section of the multi-element positive electrode material DP3 prepared in Comparative Example 3;

[0039] FIG5 is an ion milling cross-sectional view of the multi-element cathode material P4 prepared in Example 4;

[0040] FIG6 is a cross-sectional view of the ion milling of the multi-element positive electrode material DP1 prepared in Comparative Example 1;

[0041] FIG7 is a single-fold cross-sectional SEM image of a positive electrode sheet made from the multi-element positive electrode material P1 of Example 1;

[0042] FIG8 is a SEM image of a bifold cross-section of a positive electrode sheet made from the multi-element positive electrode material P1 of Example 1;

[0043] FIG9 is a single-fold cross-sectional SEM image of a positive electrode sheet made from the multi-element positive electrode material DP1 of Comparative Example 1;

[0044] FIG10 is a SEM image of a bifold cross section of a positive electrode sheet made from the multi-element positive electrode material DP1 of Comparative Example 1.

[0045] Detailed Description of the Invention

[0046] The endpoints of the ranges and any values ​​disclosed herein 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 endpoints of each range, the endpoints of each range and 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 considered to be specifically disclosed herein.

[0047] A first aspect of the present invention provides a multi-element positive electrode material, wherein the multi-element positive electrode material is a secondary particle formed by agglomeration of primary particles, wherein the ratio of the total cross-sectional area of ​​the primary particles having 5 or more grain boundaries to the cross-sectional area of ​​the secondary particles is ≥3:4; and the porosity of the cross-sectional area of ​​the secondary particles is ≤2%;

[0048] The grain boundary refers to the outline of the interface between primary particles with the same structure but different orientations on the cross section of the secondary particle, and the length of the grain boundary is ≥0.1 μm.

[0049] In the present invention, unless otherwise specified, the cross section of the secondary particle refers to the cross section after ion milling, preferably refers to the cross section after ion milling with a cross-sectional diameter equal to the DB of the secondary particle. 50 When the grain boundaries meet the above conditions, the grain boundaries between the primary particles in the cross-section of the secondary particles are radially disordered, and the primary particles in the cross-section of the secondary particles are arranged in a canine-tooth pattern. Under extreme compaction, the secondary particles creep and are not easily broken. When the multi-element positive electrode material is used in a positive electrode plate, the plate fracture can be reduced.

[0050] In some embodiments of the present invention, preferably, the number of grain boundaries with a length of ≤1.5 μm accounts for more than 70% of the total number of grain boundaries; further preferably, the number of grain boundaries with a length of ≤1.2 μm accounts for more than 70% of the total number of grain boundaries; more preferably, the number of grain boundaries with a length selected from 0.2-1.2 μm accounts for more than 80% of the total number of grain boundaries.

[0051] In the present invention, the number of grain boundaries with a length of ≤1.5μm accounts for more than 70% of the total number of grain boundaries, which means the contour lines of the interfaces between primary particles with the same structure but different orientations on the cross-section of the secondary particles, wherein the number of contour lines with a length of 0.1μm≤≤1.5μm and the total number of contour lines with a length of ≥0.1μm account for more than 70%; that is, the number of grain boundaries with a length of 0.1μm≤≤1.5μm and the total number of grain boundaries with a length of ≥0.1μm account for more than 70%.

[0052] Similarly, the number of grain boundaries with a length of ≤1.2μm accounts for more than 70% of the total number of grain boundaries, which means the number of grain boundaries with a length of 0.1μm≤≤1.2μm, and the total number of grain boundaries with a length ≥0.1μm accounts for more than 70%; the number of grain boundaries with a length selected from 0.2-1.2μm accounts for more than 80% of the total number of grain boundaries, which means the number of grain boundaries with a length of 0.2μm≤≤1.2μm, and the total number of grain boundaries with a length ≥0.1μm accounts for more than 80%.

[0053] In some embodiments of the present invention, preferably, the grain boundary density of the secondary particles is ≥1.8, for example, 1.8, 2, 2.2, 2.5, 2.8, 3, and any value in the range consisting of any two numerical values, preferably 2-3; wherein, the grain boundary density = the number of interfaces between primary particles on the cross section of the secondary particles / the number of primary particles on the cross section of the secondary particles.

[0054] In the present invention, when the length and proportion of the grain boundaries, as well as the grain boundary density meet the above-mentioned protection range, especially the preferred protection range, the primary particles in the multi-element positive electrode material show obvious disordered distribution, and at the same time will not cause cracking of the positive electrode active material particles caused by charging and discharging, and maintain sufficient cycle characteristics.

[0055] In some embodiments of the present invention, the average aspect ratio of the primary particles is preferably ≤ 1.5, for example, 0.8, 0.9, 1, 1.02, 1.05, 1.08, 1.1, 1.3, 1.5, and any value within a range consisting of any two values, preferably selected from 1-1.5, more preferably 1-1.1. When the above conditions are met, the primary particles have a smaller average aspect ratio, which facilitates their stacking and increases the packing density of the primary particles between the secondary particles.

[0056] In this invention, aspect ratio is synonymous with length-to-width ratio, i.e., the ratio of the longest diameter through the interior of a particle to the longest diameter perpendicular to it. This parameter is used to describe particle morphology and determine whether its shape is close to a regular shape. The average aspect ratio in this invention refers to the average aspect ratio of all primary particles in the cross section of a secondary particle.

[0057] In some embodiments of the present invention, it is further preferred that the primary particles have an aspect ratio of 0.9 to 1.1 and account for ≥ 70%. When these conditions are met, the primary particles are less likely to be directed into a radial arrangement when agglomerated to form secondary particles, and are more likely to change their stacking pattern when subjected to pressure, causing the secondary particles to deform without breaking.

[0058] In some embodiments of the present invention, preferably, the average particle size DB of the secondary particles 50 The average particle size DA of the primary particles 50 Satisfy: 10≤DB 50 / DA 50 ≤40, for example, 10, 15, 20, 25, 30, 35, 40, and any value in the range of any two values. In the present invention, when D A50 With D B50 When the above formula is satisfied, the secondary particles are composed of an appropriate amount of primary particles and are tightly bound to each other, thereby increasing the strength of the secondary particles; at the same time, they have good electrical properties.

[0059] In the present invention, the secondary particles are spherical or nearly spherical. Preferably, the average particle size DB of the secondary particles is 50 The thickness is selected from 6-14 μm, for example, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, and any value in a range consisting of any two values, preferably 8-12 μm.

[0060] In some embodiments of the present invention, preferably, the average particle size DA of the primary particles is 50 is selected from 0.1-1.5 μm, for example, 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, and any value in the range of any two values, preferably 0.2-1.2 μm. A50 When the above range is met, the primary particles in the multi-element positive electrode material have a smaller average particle size and dense stacking, which is conducive to forming a stable structure, alleviating the internal stress during the battery charging and discharging process, and slowing down the generation of microcracks.

[0061] In some embodiments of the present invention, preferably, the multi-element cathode material has a composition shown in Formula I: Lia (Ni x Co y Mn z M b )G c O2(I);

[0062] Wherein, 1≤a≤1.2, 0≤b≤0.05, 0≤c≤0.05, 0.3≤x<1, 0<y<0.5, 0<z<0.5, and x+y+z+b=1; M and G are each independently selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, B, Al, Co and Y.

[0063] In some embodiments of the present invention, further preferably, in Formula I, 1≤a≤1.1, 0<b≤0.02, 0<c≤0.02, 0.4≤x≤0.95, 0.01≤y≤0.2, 0.01≤z≤0.3; M is selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, Co and Y; G is selected from at least one element of Mg, Ti, W, Zr, Ce, Er, Si, B and Al.

[0064] In some embodiments of the present invention, more preferably, in Formula I, 0.0001≤b≤0.02, 0.0001≤c≤0.02, M is selected from at least one element of W, Zr, La and Y; and G is selected from at least one element of B, Ti, W, Si and Al.

[0065] In some embodiments of the present invention, preferably, in the XRD diffraction pattern, the half-maximum width (FWHM) of the characteristic diffraction peak of the multi-element cathode material at the (104) crystal plane is (104) The range is selected from 0.2-0.24, for example, 0.2, 0.22, 0.23, 0.24, and any value in the range consisting of any two values, preferably 0.22-0.24.

[0066] In the present invention, on the one hand, when the half maximum width FWHM of the characteristic diffraction peak of the (104) crystal plane is (104) When the above conditions are met, the multi-element cathode material has better crystallization performance and cycle performance; at the same time, the grains can be fully developed, so that there are more grain boundaries in the primary particles. The crystal arrangement at the grain boundaries is very irregular, and the crystal faces are interlaced and interlocked. Therefore, under normal pressure, the multi-element cathode material can have a stable structure. At the same time, because the strength at the grain boundaries is relatively low, the secondary particles are prone to creep under high pressure, thereby reducing the squeezing of the secondary balls on the aluminum foil pole piece and reducing the breakage of the pole piece. On the other hand, when the half-maximum width (FWHM) of the characteristic diffraction peak of the (104) crystal plane is (104)When the above conditions are met, there is less adhesion between the secondary particles, which can increase the compaction density of the multi-element positive electrode material and further reduce the occurrence of positive electrode sheet fracture.

[0067] In some embodiments of the present invention, preferably, the multi-element positive electrode material has a single α-NaFeO2 type layered structure.

[0068] In some embodiments of the present invention, preferably, the powder compaction density of the multi-element positive electrode material is ≥3.4 g / cm 3 The multi-element cathode material provided by the present invention has a relatively high powder compaction density, thereby increasing the energy density of the lithium battery to a certain extent.

[0069] In some embodiments of the present invention, preferably, the total residual alkali content of the multi-element positive electrode material satisfies: m(Li2CO3)+m(LiOH)<6000ppm; further preferably, the total residual alkali content of the multi-element positive electrode material also satisfies: m(Li2CO3)<m(LiOH), and both m(Li2CO3) and m(LiOH) are lower than 3000ppm.

[0070] In the present invention, when the total residual alkali content of the multi-element positive electrode material meets the above conditions, the lattice structure of the obtained multi-element positive electrode material is stable and complete, which can significantly enhance the structural stability, capacity rate performance and safety performance of the positive electrode material, thereby further improving the cycle stability of the multi-element positive electrode material; at the same time, the reduction in the amount of residual alkali can also reduce the adhesion between particles, increase the compaction density of the material, and further reduce the occurrence of electrode breakage.

[0071] A second aspect of the present invention provides a method for preparing a multi-element positive electrode material, the method comprising the following steps:

[0072] (1) mixing a precursor having a composition represented by formula II and a lithium source to obtain a mixture I, wherein the precursor is formed by agglomeration of primary crystals, and the primary crystals on a cross section of the precursor are non-radially distributed;

[0073] (2) sintering the mixture I once in an oxygen-containing atmosphere to obtain a process product; the conditions of the primary sintering include: heating the mixture to T1 at a heating rate of V1 and maintaining the temperature at t1; then heating the mixture to T2 at a heating rate of V2 and maintaining the temperature at t2;

[0074] (3) mixing the in-process product and an optional coating agent containing G to obtain a mixture II;

[0075] (4) sintering the product or mixture II twice in an oxygen-containing atmosphere to obtain a multi-element positive electrode material;

[0076] Among them, (Niα Co β Mn γ M δ )(OH)2(II), 0.3≤α<1, 0<β<0.5, 0<γ<0.5, 0≤δ≤0.05, and α+β+γ+δ=1; M and G are each independently selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, B, Al, Co and Y.

[0077] In some embodiments of the present invention, preferably, in formula II, 0.4≤α≤0.95, 0.01≤β≤0.2, 0.01≤γ≤0.3, 0<δ≤0.02, and α+β+γ+δ=1, M is selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, Co and Y; further preferably, in formula II, 0.0001≤δ≤0.02, M is selected from at least one element of W, Zr, La and Y.

[0078] The inventors of the present invention have discovered that adding a specific doping element M to the positive electrode material contributes to the disordered distribution of primary particles. Furthermore, the doping element M is distributed at the interface in an amorphous state. When squeezed, the doping element M acts as a lubricant, preventing secondary particles from breaking easily and causing only relative displacement. This mitigates the occurrence of electrode fragmentation while also ensuring that the material's electrical properties are unaffected. Compared to adding a dopant containing the element M during the compounding process, adding a dopant containing the element M during the wet coprecipitation synthesis process of the precursor stabilizes the internal structure of the material and improves the cycle life of the ternary material, particularly the high-nickel ternary material. Furthermore, the doping element M can be more evenly distributed in the positive electrode material, facilitating the disordered distribution of primary particles.

[0079] At the same time, the present invention also optimizes the sintering process. Specifically, the lithium source and the precursor adopt a double-stage heat preservation one-time sintering process, so that the lithium source slowly and fully reacts with the precursor. The obtained process product is then coated to finally obtain a multi-element positive electrode material with fully grown grains and disordered grains.

[0080] In some embodiments of the present invention, preferably, the D of the precursor 50 Selected from 8-14 μm; the specific surface area of ​​the precursor is selected from 3-7m 2 / g.

[0081] In some embodiments of the present invention, preferably, the amounts of the precursor and the lithium source satisfy n(Ni+Co+Mn+M):n(Li)=1:1-1.2, preferably satisfying n(Ni+Co+Mn+M):n(Li)=1:1-1.1.

[0082] In some embodiments of the present invention, preferably, the precursor is prepared by the following method: in an inert atmosphere, a mixed metal salt solution containing a nickel source, a cobalt source, a manganese source and an optional M-containing dopant is contacted with a precipitant, a complexing agent and a dispersant to carry out a co-precipitation reaction, and the obtained co-precipitation reaction product is washed and dried in sequence to obtain the precursor.

[0083] In the present invention, unless otherwise specified, the inert atmosphere includes but is not limited to nitrogen atmosphere, argon atmosphere, etc.

[0084] In some embodiments of the present invention, preferably, the coprecipitation reaction conditions include: a temperature selected from 40-80°C, a pH value of 10-13, and a stirring speed selected from 200-550 rpm. More preferably, the coprecipitation reaction conditions include: a temperature selected from 50-70°C, a pH value of 11-12.5, and a stirring speed selected from 350-500 rpm.

[0085] In the present invention, by controlling the conditions of the coprecipitation reaction, especially by adding the doping element M, the pH value and the stirring speed are kept within the specified range, thereby maintaining the disordered growth of the seed crystals, making the primary grains non-radially disordered, and obtaining a precursor with disordered internal grains.

[0086] In some embodiments of the present invention, preferably, in the mixed metal salt solution, the amounts of the nickel source, cobalt source, manganese source and dopant satisfy n(Ni):n(Co):n(Mn):n(M), 0.3≤n(Ni)<1, 0<n(Co)<0.5, 0<n(Mn)<0.5, 0≤n(M)≤0.05; further preferably, 0.4≤n(Ni)≤0.95, 0.01≤n(Co)≤0.2, 0.01≤n(Mn)≤0.3, 0<n(M)≤0.02; more preferably, 0.0001≤n(M)≤0.02.

[0087] In some embodiments of the present invention, preferably, the concentration of the mixed metal salt solution is 1-3 mol / L, calculated as metal elements.

[0088] In some embodiments of the present invention, preferably, the nickel source, cobalt source, manganese source, and dopant are each independently selected from at least one of sulfates, chlorates, nitrates, and acetates. In the present invention, the nickel source is selected from at least one of nickel sulfate, nickel chlorate, nickel nitrate, and nickel acetate; the cobalt source is selected from at least one of cobalt sulfate, cobalt chlorate, cobalt nitrate, and cobalt acetate; and the manganese source is selected from at least one of manganese sulfate, manganese chlorate, manganese nitrate, and manganese acetate.

[0089] In some embodiments of the present invention, preferably, the dopant is selected from soluble salts containing M, preferably at least one selected from sulfates, chlorides, hydroxides and carbonates containing M.

[0090] In a specific embodiment of the present invention, the dopant is selected from at least one of sulfates, chlorides, hydroxides and carbonates containing Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, B, Al, Co and Y, preferably selected from at least one of sulfates, chlorides, hydroxides and carbonates containing Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, Co and Y, more preferably selected from at least one of sulfates, chlorides, hydroxides and carbonates containing W, Zr, La and Y.

[0091] In a specific embodiment of the present invention, the precipitant is selected from NaOH and / or KOH; the complexing agent is selected from at least one of ammonia water, disodium edetate, ammonium nitrate, ammonium chloride and ammonium sulfate; and the dispersant is selected from at least one of polyethylene glycol (PEG), polyvinyl alcohol (PVA) and polyglycerol.

[0092] In a specific embodiment of the present invention, the precipitant, complexing agent and dispersant are each independently present in the form of an aqueous solution; further preferably, the concentration of the precipitant solution is 2-15 mol / L; the concentration of the complexing agent solution is 1-15 mol / L; and the concentration of the dispersant solution is 1-200 g / L.

[0093] In the present invention, the washing is intended to remove substances remaining on the surface of the coprecipitation reaction product; the drying is intended to remove moisture remaining on the surface of the coprecipitation reaction product. Preferably, the drying temperature is 105-130°C.

[0094] In some embodiments of the present invention, preferably, in step (2), the conditions for the primary sintering include: a heating rate V1 selected from 1-6°C / min, preferably selected from 1-3°C / min, more preferably selected from 1-2°C / min; T1 selected from 400-760°C, preferably selected from 500-750°C; a holding time t1 selected from 2-6h, preferably selected from 3-5h; a heating rate V2 selected from 1-6°C / min, preferably selected from 1-3°C / min; T2 selected from 710-950°C, preferably selected from 710-920°C; a holding time t2 selected from 5-13h, preferably selected from 6-12h.

[0095] In the present invention, a two-stage platform sintering process is used to prepare a multi-element positive electrode material, which has the advantages of low residual alkali, disordered internal structure, and stable structure. That is, in step (2), by setting appropriate heating rates (i.e., V1 and V2), holding temperatures (i.e., T1 and T2), and holding times (t1 and t2), the material undergoes a sintering treatment on two platforms, so that the lithium source and the precursor fully react, and the primary particles grow along various crystal directions after growth, thereby obtaining a pressure-resistant agglomerated positive electrode material with disordered internal structure.

[0096] In some preferred embodiments of the present invention, when the nickel content of the precursor is ≥60 mol%, calculated as the metal element, the oxygen concentration in the oxygen-containing atmosphere is ≥92 vol%. This configuration provides sufficient oxygen concentration to minimize the mixing of nickel and lithium ions when the nickel content is high, thereby reducing the residual alkali content of the material.

[0097] In some embodiments of the present invention, preferably, the primary sintered product is cooled to room temperature and then crushed to obtain the in-process product. In the present invention, the crushing includes but is not limited to at least one of a jaw crusher, a roller crusher, a colloid mill, a mechanical mill, and a jet mill.

[0098] In some embodiments of the present invention, preferably, in step (3), the amounts of the process product and the coating agent satisfy n(Ni+Co+Mn+M):n(G)=1:n(G), wherein 0≤n(G)≤0.05, preferably 0<n(G)≤0.02, and more preferably 0.0001≤n(G)≤0.02.

[0099] In some embodiments of the present invention, preferably, the coating agent is selected from at least one of oxides, hydroxides and carbonates containing G, preferably selected from at least one of oxides, hydroxides and carbonates containing Mg, Ti, W, Zr, Ce, Er, Si, B and Al, more preferably selected from at least one of oxides, hydroxides and carbonates containing B, Ti, W, Si and Al.

[0100] In some embodiments of the present invention, preferably, in step (4), the conditions for the secondary sintering include: temperature T3 selected from 300-800°C, preferably selected from 400-700°C; time t3 selected from 4-10h, preferably selected from 5-8h.

[0101] In the present invention, the multi-element cathode material prepared according to the above preparation method has a composition shown in Formula I: Li a (Ni x Co y Mn z M b )G c O2 (I);

[0102] Wherein, 1≤a≤1.2, 0≤b≤0.05, 0≤c≤0.05, 0.3≤x<1, 0<y<0.5, 0<z<0.5, and x+y+z+b=1; M and G are each independently selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, B, Al, Co and Y.

[0103] In some embodiments of the present invention, preferably, in Formula I, 1≤a≤1.1, 0<b≤0.02, 0<c≤0.02, 0.4≤x≤0.95, 0.01≤y≤0.2, 0.01≤z≤0.3; M is selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, Co and Y; G is selected from at least one element of Mg, Ti, W, Zr, Ce, Er, Si, B and Al.

[0104] In some embodiments of the present invention, further preferably, in Formula I, 0.0001≤b≤0.02, 0.0001≤c≤0.02, M is selected from at least one element of W, Zr, La and Y; and G is selected from at least one element of B, Ti, W, Si and Al.

[0105] A third aspect of the present invention provides a positive electrode plate, wherein the active material layer of the positive electrode plate contains the multi-element positive electrode material provided by the first aspect, or the multi-element positive electrode material prepared by the preparation method provided by the second aspect.

[0106] In the present invention, unless otherwise specified, the positive electrode sheet includes a positive electrode current collector and an active material layer supported on the positive electrode current collector.

[0107] In some embodiments of the present invention, the active material layer contains not only the multi-element positive electrode material, but also a conductive agent, a binder, and a dispersant.

[0108] In a specific embodiment of the present invention, the positive electrode sheet is prepared by the following method: the above-mentioned multi-element positive electrode material, SuperP, CNT and polyvinylidene fluoride (PVDF) are fully mixed with an appropriate amount of N-methylpyrrolidone (NMP) in a mass ratio of 97:1:0.8:1.2 to form a uniform slurry, the slurry is coated on aluminum foil, and after a drying process, a die-cutting machine is used to punch out a 112mm×40mm electrode sheet, wherein the multi-element positive electrode material loading is 380±2g / m 2 .

[0109] The present invention's method for determining electrode fragmentation involves baking the prepared positive electrode sheets in a vacuum oven at 125°C for at least 8 hours. The sheets are then tested by rolling them twice to a desired compaction density. The sheets are then folded using a fixed-weight flat plate. Finally, light transmission is observed using an LED point light source. The thickness and length of the positive electrode sheets before and after rolling are recorded, and the compression ratio and elongation of the positive electrode sheets before and after rolling are calculated. The positive electrode sheets are then pressed to different compaction densities, and the light transmission of the sheets when folded single-fold, double-fold, triple-fold, and quadruple-folded at different compaction densities is observed and statistically analyzed. The presence of light transmission determines the electrode fragmentation.

[0110] In addition to the above method for determining electrode fragmentation, the present invention can also use the above multi-element positive electrode materials according to the same formula to make battery electrodes, then apply a certain pressure to the electrode and observe the cross-section of the battery electrode under SEM. The electrode fragmentation can be determined based on the cross-sectional appearance.

[0111] In some embodiments of the present invention, preferably, the ultimate compaction density of the positive electrode sheet is selected from 3.2-3.8 g / cm 3 , for example, 3.2 g / cm 3 , 3.3g / cm 3 、3.5g / cm 3 、3.6g / cm 3 、3.7g / cm 3 、3.8g / cm 3 , and any value in the range of any two values, preferably 3.3-3.7 g / cm 3 .

[0112] In some embodiments of the present invention, preferably, the thickness compression ratio of the positive electrode sheet is selected from 25-45%, for example, 25%, 30%, 32%, 35%, 38%, 40%, 45%, and any value in the range of any two values, preferably 30-40%.

[0113] In some embodiments of the present invention, preferably, the elongation of the positive electrode sheet is selected from 1.2-3%, for example, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 3%, and any value in the range of any two values, preferably 1.5-2.5%.

[0114] In the present invention, the positive electrode sheet made of the multi-element positive electrode material can withstand a large rolling pressure and is not prone to breaking.

[0115] A fourth aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the positive electrode sheet prepared according to the third aspect.

[0116] The present invention will be described in detail below through examples.

[0117] (1) The compositions of the precursor and multi-element cathode materials were measured using the ICP method; the instrument used was a PE Optima 7000DV, and the test conditions were as follows: 0.1 g of sample was completely dissolved in a mixed acid solution of 3 mL HNO3 + 9 mL HCl and diluted to 250 mL for testing;

[0118] (2) Obtaining a cross-section of secondary particles: In the present invention, there are two ways to obtain a cross-section of secondary particles. One is a SEM image of a cross-section as shown in Figures 1-4. The cross-section is obtained by placing a small amount of the material to be tested on a glass slide, then squeezing the material with another glass slide, selecting a cross-section obtained by squeezing from the center of the secondary particle, and observing the cross-section under a scanning electron microscope to obtain the cross-section of the secondary particle of the present invention. This method facilitates three-dimensional observation.

[0119] The second is the ion milling cross-section shown in Figures 5-6. This cross-section is useful for clearly defining the grain boundaries mentioned in this article. The cross-section is obtained as follows:

[0120] S1. Sample preparation: a. Cut 2×4cm 2 Aluminum foil and 1.5×1.5cm 2 a. Prepare silicon wafers of standard specifications, fold the aluminum foil in half, flatten both sides, and reserve a gap in the middle for placing the sample; b. Add conductive glue to the positive electrode material powder and mix evenly, then pick up the mixed material and place it in the reserved gap of the aforementioned aluminum foil, then place the aluminum foil on the platform, use a flat plate to compact the periphery of the sample first, and then gently press the middle of the sample to obtain a pretreated sample, mark the side of the pretreated sample that contacts the platform as the front side, and the pressed side as the back side; c. Dry the pretreated sample at 100°C for 60 minutes, take out the pretreated sample after drying, cut off the excess aluminum foil on the pretreated sample without sample, and then cut the sample vertically from the back side at a location with sufficient sample; d. Take the above-mentioned silicon wafer, use glue to stick the back side of the cut pretreated sample to the silicon wafer, so that the relatively flat front side of the sample can be close to the baffle and face the ion beam positively. When pasting, ensure that the cut surface of the aluminum foil protrudes from the edge of the silicon wafer or is flush with it, for example, protruding by more than 60μm, to obtain the sample to be tested.

[0121] S2. Measurement: Glue conductive tape on the side of the sample stage and fix the sample to be tested on the sample stage, wherein the upper edge of the sample to be tested should be about 1-3 mm higher than the sample stage. Then perform ion milling on the sample to be tested on the sample stage. After milling, apply liquid conductive glue in the gap between the silicon wafer and the sample to be tested to increase conductivity. Finally, place the treated sample stage on a sample stage holder dedicated to the electron microscope, fix the position of the sample stage with an inner hexagon, and obtain a cross-sectional sample by electron microscope observation. The ion milling instrument used in the present invention is a Hitachi ion milling instrument IM4000PLUS. Please refer to Table 1 for ion milling conditions:

[0122] Table 1

[0123] In the ion milling profile obtained based on the above method, it is necessary to screen out particles with a cross-sectional diameter of 8-12 μm for observation based on the average particle size of the secondary particles defined in the present invention, because the cross-sections within this diameter range pass through or are close to the center of the sphere and are more representative. When performing ion milling, the ion milling instrument should first be set to STAGE CONT C4 mode, with an operating time of 40 minutes, an acceleration voltage of 6 kV, a maximum discharge voltage, and an airflow of 0.09 cm3 / min. The electron microscope test conditions are low voltage backscatter mode, voltage = 1 kV, WD = 2.5 mm, and a magnification of 10k.

[0124] (3) Grain boundary determination criteria: In the present invention, grain boundaries are determined based on ion milling cross-sections. A grain boundary is defined as the interface between primary particles with the same structure but different orientations on the cross-section of a secondary particle, and the length of the interface is ≥0.1 μm.

[0125] (4) Morphology test: obtained by scanning electron microscope S-4800 model of Hitachi HITACHI Company, Japan;

[0126] (5) Particle size DA 50 、DB 50 : Measured by Malvern's Mastersize 2000 laser particle size analyzer;

[0127] (6) Compacted density: obtained by testing using a BT-30 tap density tester from Baxter.

[0128] The compositions and physical properties of the precursors prepared in Preparation Examples 1-5 and Comparative Preparation Examples 1-4 are listed in Table 2.

[0129] Preparation Example 1

[0130] Prepare a 2 mol / L mixed metal salt solution, where the molar ratios of nickel sulfate, cobalt sulfate, manganese sulfate, and yttrium sulfate are 0.5:0.2:0.2985:0.0015, respectively, calculated as metal elements; prepare a 3 mol / L NaOH solution, prepare a 3 mol / L ammonia solution, and prepare a 10 g / L PVA dispersant aqueous solution;

[0131] Under a nitrogen atmosphere, the above solutions were introduced into the reactor in parallel for co-precipitation reaction, maintaining the reaction temperature at 50°C, the reaction pH at 11.2, and the stirring speed at 350 rpm. After washing, drying at 120°C, and sieving, the precursor S1 was obtained.

[0132] The SEM image of the cross section of the precursor S1 is shown in FIG1 . As can be seen from FIG1 , the precursor S1 is formed by agglomeration of primary crystal grains, and the primary crystal grains on the cross section of the precursor S1 are randomly distributed.

[0133] Preparation Example 2

[0134] The method of Preparation Example 1 was followed, except that

[0135] The type of dopant was replaced with zirconium chloride;

[0136] A 2 mol / L mixed metal salt solution was prepared, wherein the molar ratios of nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium chloride in the mixed metal salt solution were 0.6:0.2:0.1985:0.0015, respectively, based on the metal elements.

[0137] The stirring speed was changed to 450 rpm, and the type of dispersant was replaced with a 10 g / L aqueous solution of PEG1000 dispersant;

[0138] The other conditions are the same to obtain precursor S2.

[0139] The SEM image of the cross section of the precursor S2 is similar to that in FIG1 .

[0140] Preparation Example 3

[0141] The method of Preparation Example 1 was followed, except that

[0142] The dopant type was replaced with lanthanum nitrate;

[0143] A 2 mol / L mixed metal salt solution was prepared, wherein the molar ratios of nickel sulfate, cobalt sulfate, manganese sulfate, and lanthanum nitrate in the mixed metal salt solution were 0.81:0.09:0.0985:0.0015, respectively, based on the metal elements.

[0144] The concentration of ammonia water was replaced with 4 mol / L;

[0145] The coprecipitation reaction conditions were changed to a reaction temperature of 55°C, a reaction pH of 11.7, and a stirring speed of 450 rpm;

[0146] The other conditions were the same to obtain precursor S3.

[0147] The SEM image of the cross section of the precursor S3 is similar to that in FIG1 .

[0148] Preparation Example 4

[0149] The method of Preparation Example 1 was followed, except that

[0150] The dopant type was replaced with sodium tungstate and yttrium sulfate;

[0151] A 2 mol / L mixed metal salt solution was prepared, wherein the molar ratios of nickel sulfate, cobalt sulfate, manganese sulfate, sodium tungstate, and yttrium sulfate in the mixed metal salt solution were 0.95:0.02:0.0275:0.001:0.0015, respectively, based on the metal elements;

[0152] The concentration of NaOH was replaced with 4 mol / L;

[0153] The dispersant used was a 10 g / L aqueous solution of PEG1000 dispersant;

[0154] The reaction pH value of the coprecipitation reaction was changed to 12.1, and the stirring speed was changed to 400 rpm;

[0155] The other conditions were the same to obtain precursor S4.

[0156] The SEM image of the cross section of the precursor S4 is similar to that in FIG1 .

[0157] Preparation Example 5

[0158] The method of Preparation Example 4 was followed, except that no dopant (sodium tungstate and yttrium sulfate) was added.

[0159] That is, a 2 mol / L mixed metal salt solution was prepared, wherein the molar ratios of nickel sulfate, cobalt sulfate, and manganese sulfate in the mixed metal salt solution were 0.95:0.02:0.03, respectively, based on the metal elements.

[0160] The other conditions were the same to obtain precursor S5;

[0161] The SEM image of the cross section of the precursor S5 is similar to that in FIG1 .

[0162] Comparative Preparation Example 1

[0163] The method of Preparation Example 1 was followed, except that

[0164] No dopant yttrium sulfate was added, that is, a 2 mol / L mixed metal salt solution was prepared, wherein the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate in the mixed metal salt solution was 50:20:30, calculated as metal elements;

[0165] The coprecipitation reaction conditions were changed to a reaction temperature of 60°C, a reaction pH of 11.7, and a stirring speed of 800 rpm;

[0166] The other conditions were the same to obtain precursor S1.

[0167] The SEM image of the cross section of the precursor DS1 is shown in FIG2 . As can be seen from FIG2 , the precursor DS1 is formed by agglomeration of primary crystal grains, and the primary crystal grains on the cross section of the precursor DS1 are distributed radially.

[0168] Comparative Preparation Example 2

[0169] The method of Preparation Example 2 was followed, except that

[0170] No dopant zirconium chloride is added; that is, a 2 mol / L mixed metal salt solution is prepared, wherein the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate in the mixed metal salt solution is 60:20:20, calculated as metal elements;

[0171] The concentration of NaOH solution is 2 mol / L, and the concentration of ammonia water is 2 mol / L;

[0172] The coprecipitation reaction conditions were changed to a reaction temperature of 55°C, a reaction pH of 13.2, and a stirring speed of 450 rpm;

[0173] The other conditions were the same to obtain the precursor DS2.

[0174] Among them, the SEM image of the cross section of the above-mentioned precursor DS2 is similar to Figure 2.

[0175] Comparative Preparation Example 3

[0176] The method of Preparation Example 3 was followed, except that

[0177] No dopant lanthanum nitrate was added; that is, a 2 mol / L mixed metal salt solution was prepared, wherein the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate in the mixed metal salt solution was 81:9:10, calculated as metal elements;

[0178] The coprecipitation reaction conditions were replaced by a reaction temperature of 58°C, a reaction pH of 13.2, and a stirring speed of 800 rpm;

[0179] The other conditions were the same to obtain the precursor DS3.

[0180] The SEM image of the cross section of the precursor DS3 is similar to that in FIG2 .

[0181] Comparative Preparation Example 4

[0182] The method of Preparation Example 4 was followed, except that

[0183] No doping agents, sodium tungstate and yttrium sulfate, were added; that is, a 2 mol / L mixed metal salt solution was prepared, wherein the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate in the mixed metal salt solution was 95:2:3, calculated as metal elements;

[0184] The dispersant is a 10 g / L polyglycerol dispersant aqueous solution;

[0185] The coprecipitation reaction conditions were replaced by a reaction temperature of 60°C, a reaction pH of 11.7, and a stirring speed of 600 rpm;

[0186] The other conditions were the same to obtain the precursor DS4.

[0187] The SEM image of the cross section of the precursor DS4 is similar to that in FIG2 .

[0188] Table 2

[0189] Table 2

[0190] Note: *- primary grain distribution on the precursor cross section.

[0191] Table 2

[0192] It can be seen from the data in Table 2 that compared with Comparative Preparation Examples 1-4, Preparation Examples 1-5 meet the conditions of the coprecipitation reaction by regulating: the temperature is selected from 40-80°C, the pH value is 10-13, and the stirring speed is selected from 200-550rpm. In particular, in combination with the type of doping element M, the precursor satisfying Formula II is formed by agglomeration of primary grains, and the primary grains on the cross-section of the precursor are non-radially distributed.

[0193] The process parameters of Examples 1-5 and Comparative Examples 1-8 are listed in Table 3, and the compositions and physical properties of the prepared multi-element positive electrode materials are listed in Table 4.

[0194] Example 1

[0195] (1) Precursor S1 obtained in Preparation Example 1 and lithium carbonate are mixed to obtain a mixture I; wherein the amounts of the precursor S1 and lithium carbonate satisfy n(Ni+Co+Mn+Y):n(Li)=1:1.05;

[0196] (2) The mixture I was sintered once in an air atmosphere, heated to T1 = 730°C at a heating rate of V1 = 5°C / min, and kept at this temperature for t1 = 3h; then heated to T2 = 920°C at a heating rate of V2 = 5°C / min, and kept at this temperature for t2 = 9h, and then cooled naturally to room temperature. The mixture was crushed by a crushing device and then sieved to obtain a process product with a disordered internal structure;

[0197] (3) Mixing the above-mentioned process product with MgO to obtain a uniformly coated mixture II, wherein the amounts of the above-mentioned process product and MgO satisfy n(Ni+Co+Mn+Y):n(Mg)=1:0.0012;

[0198] (4) The mixture II was subjected to secondary sintering in an air atmosphere (temperature of 700° C., time of 6 h) to obtain the multi-element positive electrode material P1.

[0199] Example 2

[0200] According to the method of Example 1, the difference is that

[0201] In step (1), the precursor is the precursor S2 prepared in Preparation Example 2; the amounts of the precursor S2 and lithium carbonate satisfy n(Ni+Co+Mn+Zr):n(Li)=1:1.06;

[0202] In step (2), the primary sintering atmosphere is an oxygen atmosphere with an oxygen content of ≥92V%;

[0203] The primary sintering conditions were changed to heating at a rate of V1 = 4 °C / min to T1 = 710 °C, holding at this temperature for t1 = 3 h; then heating at a rate of V2 = 4 °C / min to T2 = 860 °C, holding at this temperature for t2 = 10 h;

[0204] In step (3), the type of coating agent is replaced by Al2O3, and the amount of the above-mentioned process product and Al2O3 satisfies n(Ni+Co+Mn+Zr):n(Al)=1:0.001;

[0205] The remaining conditions are the same to obtain the multi-element positive electrode material P2.

[0206] Example 3

[0207] According to the method of Example 1, the difference is that

[0208] In step (1), the precursor is the precursor S3 prepared in Preparation Example 3; the amounts of the precursor S3 and lithium hydroxide satisfy n(Ni+Co+Mn+La):n(Li)=1:1.02;

[0209] In step (2), the primary sintering atmosphere is an oxygen atmosphere with an oxygen content of ≥95V%;

[0210] The primary sintering conditions were changed to heating at a rate of V1 = 2 °C / min to T1 = 600 °C, holding at that temperature for t1 = 4 h; then heating at a rate of V2 = 2 °C / min to T2 = 785 °C, holding at that temperature for t2 = 8 h;

[0211] In step (3), the coating agent is replaced by CeO2, and the amount of the above-mentioned process product and CeO2 satisfies n(Ni+Co+Mn+La):n(Ce)=1:0.0008;

[0212] In step (4), the secondary sintering temperature is replaced with 500°C;

[0213] The remaining conditions were the same to obtain the multi-element positive electrode material P3.

[0214] The SEM image of the cross section of the multi-element positive electrode material P3 is shown in FIG3 . As can be seen from FIG3 , the internal particles of the multi-element positive electrode material P3 are disordered and grow in a non-radial manner.

[0215] Example 4

[0216] The method of Example 1 is as follows, except that

[0217] In step (1), the precursor is the precursor S4 prepared in Preparation Example 4; the amounts of the precursor S4 and lithium hydroxide satisfy n(Ni+Co+Mn+W+Y):n(Li)=1:1.03;

[0218] In step (2), the primary sintering atmosphere is an oxygen atmosphere with an oxygen content of ≥95V%;

[0219] The primary sintering conditions were changed to heating at a rate of V1 = 2 °C / min to T1 = 600 °C, holding at that temperature for t1 = 4 h; then heating at a rate of V2 = 2 °C / min to T2 = 725 °C, holding at that temperature for t2 = 8 h;

[0220] In step (3), the type of coating agent is replaced by B2O3, and the amount of the above-mentioned process product and B2O3 satisfies n(Ni+Co+Mn+W+Y):n(B)=1:0.001;

[0221] In step (4), the secondary sintering temperature is replaced with 350°C;

[0222] The other conditions are the same to obtain the multi-element positive electrode material P4.

[0223] The ion milling cross-section of the multi-element positive electrode material P4 is shown in FIG5 . As can be seen from FIG5 , the internal particles of the multi-element positive electrode material P4 are disordered and grow in a non-radial manner.

[0224] Example 5

[0225] The method of Example 4 is as follows, except that

[0226] In step (1), the precursor is the precursor S5 prepared in Preparation Example 5;

[0227] The dopants used are tungsten oxide and yttrium oxide, wherein the amounts of the above-mentioned precursor S5, tungsten oxide, yttrium oxide and lithium hydroxide satisfy: n(Ni):n(Co):n(Mn):n(W)n(Y):n(Li)=0.95:0.02:0.0275:0.001:0.0015:1.03.

[0228] The remaining conditions were the same to obtain the multi-element positive electrode material P5.

[0229] Comparative Example 1

[0230] The method of Example 1 is as follows, except that

[0231] In step (1), the precursor is the precursor DS1 prepared in Comparative Preparation Example 1;

[0232] The remaining conditions were the same to obtain the multi-element positive electrode material DP1.

[0233] The ion milling cross-section of the multi-element positive electrode material DP1 is shown in FIG6 . As can be seen from FIG6 , the internal particles of the multi-element positive electrode material DP1 grow in a radial distribution.

[0234] Comparative Example 2

[0235] According to the method of Example 2, the difference is that

[0236] In step (1), the precursor is the precursor DS2 prepared in Comparative Preparation Example 2;

[0237] The remaining conditions were the same to obtain the multi-element positive electrode material DP2.

[0238] Comparative Example 3

[0239] The method of Example 3 is followed, except that

[0240] In step (1), the precursor is the precursor DS3 prepared in Comparative Preparation Example 3;

[0241] The remaining conditions were the same to obtain the multi-element positive electrode material DP3.

[0242] The SEM image of the cross section of the multi-element positive electrode material DP3 is shown in FIG4 . As can be seen from FIG4 , the internal particles of the multi-element positive electrode material DP3 grow in a radial distribution.

[0243] Comparative Example 4

[0244] The method of Example 4 is as follows, except that

[0245] In step (1), the precursor is the precursor DS4 prepared in Comparative Preparation Example 4;

[0246] The remaining conditions were the same to obtain the multi-element positive electrode material DP4.

[0247] Comparative Example 5

[0248] According to the method of Example 1, the difference is that

[0249] In step (2), t1 is 0 h;

[0250] The other conditions were the same to obtain the multi-element positive electrode material DP5.

[0251] Comparative Example 6

[0252] According to the method of Example 2, the difference is that

[0253] In step (2), the conditions for the first sintering are replaced by: heating at a heating rate of V1 = 7 ° C / min to T1 = 710 ° C, and maintaining the temperature at t1 = 3 h; then heating at a heating rate of V2 = 7 ° C / min to T2 = 860 ° C, and maintaining the temperature at t2 = 10 h;

[0254] The other conditions were the same to obtain the multi-element positive electrode material DP6.

[0255] Comparative Example 7

[0256] The method of Example 3 is followed, except that

[0257] In step (2), the atmosphere for the primary sintering and the secondary sintering is an oxygen atmosphere with an oxygen content of 85V%;

[0258] The remaining conditions were the same to obtain the multi-element positive electrode material DP7.

[0259] Comparative Example 8

[0260] The method of Example 4 is as follows, except that

[0261] In step (2), the conditions for the first sintering are replaced by: heating to T1 = 600°C at a heating rate of V1 = 7°C / min; then heating to T2 = 725°C at a heating rate of V2 = 7°C / min, and maintaining the temperature for t2 = 7h;

[0262] The remaining conditions were the same to obtain the multi-element positive electrode material DP8.

[0263] Table 3

[0264] Note: 1- The molar ratio of lithium source and precursor, calculated as metal elements;

[0265] 2- The molar ratio of the above precursors and dopants, calculated as metal elements;

[0266] 3- The molar ratio of the above-mentioned process product and the coating agent, calculated as metal elements.

[0267] Table 3

[0268] Table 3

[0269] Table 4

[0270] Table 4

[0271] Note: 4 - The ratio of the total cross-sectional area of ​​primary particles with more than 5 grain boundaries to the cross-sectional area of ​​secondary particles is ≥3:4, which is recorded as √; otherwise, it is recorded as ×; 5 - The porosity on the cross-sectional surface of the secondary particles; 6 - The grain boundary density of the secondary particles = the number of interfaces between primary particles on the cross-sectional surface of the secondary particles / the number of primary particles on the cross-sectional surface of the secondary particles; 7 - The proportion of grain boundaries with a length of ≤1.5μm to the total number of grain boundaries; 8 - The proportion of primary particles with an aspect ratio selected from 0.9-1.1.

[0272] Table 4

[0273] As shown in Tables 2-4, compared to Comparative Examples 1-8, Examples 1-5, using the preparation method provided by the present invention, produce multi-element cathode materials with the advantages of disordered, non-radial internal particle growth, high compaction density, and less prone to electrode fragmentation. The materials prepared in Examples 1-4 using non-radially doped precursors via a dual-platform heat preservation process exhibit significantly higher powder compaction than the cathode materials of Comparative Examples 1-8, which were prepared using the same process with radially distributed precursors. The distribution compaction of the material in Example 5, which does not dope the element M in the precursor stage but adds the doping element M in the cathode material preparation stage, is slightly lower than that of the material in Example 4, which was prepared by doping the element M in the precursor stage.

[0274] In addition, the materials prepared by excessively high heating rates V1 and V2 (Comparative Example 6), high Ni content and insufficient oxygen concentration in the first sintering (Comparative Example 7), and single-platform one-time sintering process (Comparative Example 5, Comparative Example 8) have significantly higher alkali content and corresponding lower compaction, which makes it easier for the electrode to break when compacting.

[0275] Test Example 1

[0276] The positive electrode sheets made of the multi-element positive electrode materials of the above examples and comparative examples were subjected to limit compaction and fragmentation tests, and the test results are listed in Table 5.

[0277] The specific preparation process of the positive electrode sheet is as follows: the above-mentioned multi-element positive electrode materials, SP, CNT and polyvinylidene fluoride (PVDF) are mixed with an appropriate amount of N-methylpyrrolidone (NMP) in a mass ratio of 97:1:0.8:1.2 to form a uniform slurry, and the slurry is coated on aluminum foil. After the drying process, a die-cutting machine is used to punch out 112mm×40mm electrode sheets, in which the multi-element positive electrode material loading is 380±2g / m 2 .

[0278] Method for determining electrode fragmentation: Prepared positive electrode sheets are baked in a vacuum oven at 125°C for at least 8 hours. The sheets are then rolled twice to reach the desired compaction density. The sheets are then folded using a fixed weight flat plate. Finally, light transmission is observed using an LED point light source. The thickness and length of the positive electrode sheets before and after rolling are recorded, and the compression ratio and elongation of the positive electrode sheets before and after rolling are calculated. The positive electrode sheets are then pressed to different compaction densities. The light transmission of the sheets when folded single-fold, double-fold, triple-fold, and quadruple-folded is observed and statistically analyzed at different compaction densities. The presence of light transmission determines the fragmentation of the positive electrode sheet.

[0279] Table 5

[0280] Table 5

[0281] Note: ~ means that the test will not be performed after light is transmitted under this condition.

[0282] From the data in Table 5, it can be seen that the ultimate compaction density of the positive electrode sheet made of the multi-element positive electrode material P1 of Example 1 is 3.64 g / cm2 when single folded and double folded and opaque respectively. 3 、3.57g / cm 3 (Taking Example 1 as an example, the ultimate compaction density of the positive electrode sheet A2 corresponding to the initial single fold and opaque state, and the ultimate compaction density of the positive electrode sheet A4 corresponding to the initial double fold and opaque state) The positive electrode sheet made of the multi-element positive electrode material P2 of Example 2 was subjected to ultimate pressing, and the ultimate compaction densities corresponding to the single fold and double fold and opaque state were 3.66 g / cm 3 、3.62g / cm 3 The positive electrode sheet made of the multi-element positive electrode material P3 of Example 3 was subjected to extreme pressing. The corresponding ultimate compaction densities when single folded and double folded were 3.77 g / cm3 、3.59g / cm 3 The positive electrode sheet made of the multi-element positive electrode material P4 of Example 4 was subjected to extreme pressing. The corresponding ultimate compaction densities when single folded and double folded were 3.71 g / cm 3 、3.57g / cm 3 The compaction density of the pole pieces of these materials is higher than the corresponding comparative examples.

[0283] SEM images of the cross-section of the positive electrode sheet made from the multi-element positive electrode material P1 of Example 1 after ultimate compaction, as shown in Figures 7 (single fold) and 8 (double fold), show that under higher ultimate compaction, the secondary particles tend to soften, which is equivalent to relieving some of the rolling pressure, thereby reducing the squeezing of the secondary balls on the aluminum foil sheet and reducing the breakage of the sheet. At the same time, the electrical properties of the battery can still well meet the use requirements.

[0284] The SEM images of the cross-section of the positive electrode sheet made of the multi-component positive electrode material DP1 of Comparative Example 1 after extreme compaction are shown in Figures 9 (single fold) and 10 (double fold). Even when the secondary particles are subjected to a smaller extreme compaction, the radial distribution of the internal structure of the multi-component positive electrode material DP1 causes its secondary spheres to be difficult to deform, and the pressure acting on them is directly transferred to the aluminum foil, causing the aluminum foil to break.

[0285] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A multi-element positive electrode material, characterized in that: The multi-element positive electrode material is a secondary particle formed by agglomeration of primary particles, wherein the ratio of the total cross-sectional area of ​​the primary particles having more than 5 grain boundaries to the cross-sectional area of ​​the secondary particles is ≥3:4; and the porosity on the cross-sectional surface of the secondary particles is ≤2%; The grain boundary refers to the contour line of the interface between primary particles with the same structure but different orientations on the cross section of the secondary particle, and the length of the grain boundary is ≥0.1 μm.

2. The multi-element positive electrode material according to claim 1, wherein: The number of grain boundaries with a length of ≤1.5 μm accounts for more than 70% of the total number of grain boundaries; Preferably, the number of grain boundaries with a length of ≤1.2 μm accounts for more than 70% of the total number of grain boundaries; Further preferably, the number of grain boundaries with a length of 0.2-1.2 μm accounts for more than 80% of the total number of grain boundaries.

3. The multi-element positive electrode material according to claim 1 or 2, wherein: The grain boundary density of the secondary particles is ≥1.8, preferably selected from 2-3, wherein the grain boundary density = the number of interfaces between primary particles on the cross section of the secondary particles / the number of primary particles on the cross section of the secondary particles.

4. The multi-element positive electrode material according to any one of claims 1 to 3, wherein: The average aspect ratio of the primary particles is ≤1.5, preferably selected from 1-1.5, more preferably selected from 1-1.1; Preferably, the primary particles having an aspect ratio selected from 0.9-1.1 account for ≥70%.

5. The multi-element positive electrode material according to any one of claims 1 to 4, wherein the average particle size DB of the secondary particles is 50 The average particle size DA of the primary particles 50 Satisfy: 10≤DB 50 / DA 50 ≤40; and / or, the average particle size DB of the secondary particles 50 Selected from 6-14 μm, preferably 8-12 μm; and / or, the average particle size DA of the primary particles 50 Selected from 0.1-1.5 μm, preferably 0.2-1.2 μm.

6. The multi-element positive electrode material according to any one of claims 1 to 5, wherein: The multi-element positive electrode material has a composition shown in Formula I: Li a (Ni x Co y Mn z M b )G c O2 (I); Wherein, 1≤a≤1.2, 0≤b≤0.05, 0≤c≤0.05, 0.3≤x<1, 0<y<0.5, 0<z<0.5, and x+y+z+b=1; M and G are each independently selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, B, Al, Co and Y; Preferably, in formula I, 1≤a≤1.1, 0<b≤0.02, 0<c≤0.02, 0.4≤x≤0.95, 0.01≤y≤0.2, 0.01≤z≤0.3; M is at least one element selected from Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, Co and Y; G is at least one element selected from Mg, Ti, W, Zr, Ce, Er, Si, B and Al; Further preferably, in Formula I, 0.0001≤b≤0.02, 0.0001≤c≤0.02, M is selected from at least one element of W, Zr, La and Y; and G is selected from at least one element of B, Ti, W, Si and Al.

7. The multi-element positive electrode material according to any one of claims 1 to 6, wherein: In the XRD diffraction spectrum, the multi-element positive electrode material has a characteristic diffraction peak of the (104) crystal plane, and the half-peak width FWHM of the characteristic diffraction peak of the (104) crystal plane is (104) Selected from 0.2-0.

24.

8. The multi-element positive electrode material according to any one of claims 1 to 7, wherein: The multi-element positive electrode material has a single α-NaFeO2 type layered structure.

9. The multi-element positive electrode material according to any one of claims 1 to 8, wherein: The powder compaction density of the multi-element positive electrode material is ≥3.4 g / cm 3 .

10. The multi-element positive electrode material according to any one of claims 1 to 9, wherein: The total residual alkali content of the multi-element positive electrode material satisfies: m(Li2CO3)+m(LiOH)<6000ppm; And / or, the total residual alkali content of the multi-element positive electrode material also satisfies: m(Li2CO3)<m(LiOH), and both m(Li2CO3) and m(LiOH) are lower than 3000 ppm.

11. A method for preparing a multi-element positive electrode material, characterized in that: The preparation method comprises the following steps: (1) mixing a precursor having a composition shown in formula II and a lithium source to obtain a mixture I, wherein the precursor is formed by agglomeration of primary crystal grains, and the primary crystal grains on a cross section of the precursor are non-radially distributed; (2) sintering the mixture I once in an oxygen-containing atmosphere to obtain a process product; the conditions of the once sintering include: heating to T1 at a heating rate of V1 and maintaining a constant temperature of t1; then heating to T2 at a heating rate of V2 and maintaining a constant temperature of t2; (3) mixing the process product and an optional coating agent containing G to obtain a mixture II; (4) in an oxygen-containing atmosphere, performing secondary sintering on the process product or mixture II to obtain a multi-element positive electrode material; Among them, (Ni α Co β Mn γ M δ )(OH)2 (II), 0.3≤α<1, 0<β<0.5, 0<γ<0.5, 0≤δ≤0.05, and α+β+γ+δ=1; M and G are each independently selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, B, Al, Co and Y.

12. The preparation method according to claim 11, wherein In step (1), the precursor D 50 Selected from 8-14μm.

13. The preparation method according to claim 11 or 12, wherein: The specific surface area of ​​the precursor is selected from 3-7m 2 / g.

14. The preparation method according to any one of claims 11 to 13, wherein: The amounts of the precursor and the lithium source satisfy n(Ni+Co+Mn+M):n(Li)=1:1-1.2, preferably n(Ni+Co+Mn+M):n(Li)=1:1-1.

1.

15. The preparation method according to any one of claims 11 to 14, wherein: The precursor is prepared by the following method: in an inert atmosphere, a mixed metal salt solution containing a nickel source, a cobalt source, a manganese source and an optional M-containing dopant is contacted with a precipitant, a complexing agent and a dispersant to carry out a coprecipitation reaction, and the obtained coprecipitation reaction product is washed and dried in sequence to obtain the precursor; Preferably, the conditions of the coprecipitation reaction include: a temperature selected from 40-80°C, a pH value of 10-13, and a stirring speed selected from 200-550rpm; Further preferably, the conditions of the coprecipitation reaction include: a temperature selected from 50-70° C., a pH value selected from 11-12.5, and a stirring speed selected from 350-500 rpm.

16. The preparation method according to claim 15, wherein: In the mixed metal salt solution, the amounts of the nickel source, cobalt source, manganese source and dopant satisfy n(Ni):n(Co):n(Mn):n(M), 0.3≤n(Ni)<1, 0<n(Co)<0.5, 0<n(Mn)<0.5, 0≤n(M)≤0.05; Preferably, 0.4≤n(Ni)≤0.95, 0.01≤n(Co)≤0.2, 0.01≤n(Mn)≤0.3, 0<n(M)≤0.02; More preferably, 0.0001≤n(M)≤0.

02.

17. The preparation method according to any one of claims 11 to 16, wherein: In step (2), the conditions for the primary sintering include: The heating rate V1 is selected from 1-6°C / min, preferably 1-3°C / min, more preferably 1-2°C / min; T1 is selected from 400-760°C, preferably 500-750°C; the holding time t1 is selected from 2-6h, preferably 3-5h; The heating rate V2 is selected from 1-6°C / min, preferably from 1-3°C / min; T2 is selected from 710-950°C, preferably from 710-920°C; the insulation time t2 is selected from 5-13h, preferably from 6-12h.

18. The preparation method according to any one of claims 11 to 17, wherein: Calculated in terms of metal elements, when the nickel content in the precursor is ≥ 60 mol %, the oxygen concentration in the oxygen-containing atmosphere is ≥ 92 volume %.

19. The preparation method according to any one of claims 11 to 18, wherein: The primary sintered product is cooled to room temperature and then crushed to obtain the process product.

20. The preparation method according to any one of claims 11 to 19, wherein: In step (3), the amounts of the process product and the coating agent satisfy n(Ni+Co+Mn+M):n(G)=1:n(G), wherein 0≤n(G)≤0.05, preferably 0<n(G)≤0.02, and more preferably 0.0001≤n(G)≤0.

02.

21. The preparation method according to any one of claims 11 to 20, wherein: The coating agent is selected from at least one of oxides, hydroxides and carbonates containing G; preferably selected from at least one of oxides, hydroxides and carbonates containing Mg, Ti, W, Zr, Ce, Er, Si, B and Al, and more preferably selected from at least one of oxides, hydroxides and carbonates containing B, Ti, W, Si and Al.

22. The preparation method according to any one of claims 11 to 21, wherein: In step (4), the conditions for the secondary sintering include: temperature T3 is selected from 300-800°C, preferably selected from 400-700°C; time t3 is selected from 4-10h, preferably selected from 5-8h.

23. The preparation method according to any one of claims 11 to 22, wherein: In step (4), the multi-element positive electrode material has a composition shown in Formula I: Li a (Ni x Co y Mn z M b )G c O2 (I); Wherein, 1≤a≤1.2, 0≤b≤0.05, 0≤c≤0.05, 0.3≤x<1, 0<y<0.5, 0<z<0.5, and x+y+z+b=1; M and G are each independently selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, B, Al, Co and Y; Preferably, in Formula I, 1≤a≤1.1, 0<b≤0.02, 0<c≤0.02, 0.4≤x≤0.95, 0.01≤y≤0.2, 0.01≤z≤0.3; M is selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, Co and Y; G is selected from Mg, At least one element selected from Ti, W, Zr, Ce, Er, Si, B and Al; Further preferably, in Formula I, 0.0001≤b≤0.02, 0.0001≤c≤0.02, M is selected from at least one element of W, Zr, La and Y; and G is selected from at least one element of B, Ti, W, Si and Al.

24. A positive electrode plate, characterized in that: The active material layer of the positive electrode sheet contains the multi-element positive electrode material described in any one of claims 1-10, or the multi-element positive electrode material prepared by the preparation method described in any one of claims 11-23.

25. The positive electrode sheet according to claim 24, wherein: In the positive electrode sheet, the loading amount of the multi-element positive electrode material is 380±2g / m 2 .

26. The positive electrode sheet according to claim 24 or 25, wherein: The ultimate compaction density of the positive electrode sheet is selected from 3.2-3.8 g / cm 3 , preferably 3.3-3.7 g / cm 3 .

27. The positive electrode sheet according to any one of claims 24 to 26, wherein: The thickness compression ratio of the positive electrode plate is selected from 25-45%, preferably 30-40%.

28. The positive electrode sheet according to any one of claims 24 to 27, wherein: The elongation of the positive electrode sheet is selected from 1.2-3%, preferably 1.5-2.5%.

29. A lithium ion battery, characterized in that: The lithium-ion battery contains the positive electrode sheet described in any one of claims 24 to 28.

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