Positive electrode material, preparation method therefor, and use thereof

Abstract

A positive electrode material, a preparation method therefor and the use thereof. The Dv50 value of the positive electrode material is α, the unit being μm, the lithium richness amount of the positive electrode material is γ, and the average porosity of the positive electrode material is denoted as β％ in percentage, α, β and γ satisfying: δ=β-[2α+75γ] / 3, wherein 0≤δ≤4.0. By means of defining the relational expression of the Dv50, the average porosity and the lithium richness amount of the positive electrode material, a lithium ion battery prepared by using the positive electrode material can have excellent specific capacity, energy density, rate capability and cycle performance, and particularly can maintain excellent electrochemical properties at high voltage.

Description

A positive electrode material and its preparation method and application

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 13, 2023, with application number 202311186638.4 and application name “A positive electrode material, its preparation method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to a positive electrode material and a preparation method and application thereof, belonging to the technical field of lithium-ion batteries. Background Art

[0003] The performance of the positive electrode material directly determines the performance of the lithium-ion battery. The specific capacity, cycle performance, and rate characteristics of the positive electrode material will directly affect the energy density, service life, and fast charging performance of the lithium-ion battery. 1-x-y-z Ni x Co y Mn z ]O2) has attracted much attention due to its high specific capacity and cost advantages, but its rate performance is poor compared to ternary positive electrode materials. In the context of industrialization with increasingly higher requirements for fast charging, how to improve the rate performance of lithium-rich positive electrode materials is a research focus in this field.

[0004] The high specific capacity of lithium-rich cathode materials is mainly attributed to the reversible redox process of doped anions and the local electron vacancies formed on oxygen atoms. In actual use, in order to avoid a series of problems caused by extremely high voltages, the application voltage window can be appropriately lowered to provide excellent cycle stability at a slightly lower capacity, but the rate performance is still at a disadvantage and cannot meet the requirements of high power density, resulting in limited fast charging performance. This is because anion redox has a greater impact on the stability of the crystal structure and a slower response than cation redox, while the kinetic performance of layered ternary materials is compared to that of ternary cathode materials that only use cation redox to provide capacity. Compared with ternary cathode materials, lithium-rich cathode materials have problems such as a higher unit cell volume change rate, severe lattice distortion, and limited kinetic performance, which in turn leads to difficulties in lithium ion migration, increased polarization, voltage hysteresis, etc., which reduces the charge and discharge energy efficiency of the cathode material and makes it impossible to achieve higher rate performance.

[0005] Currently, most approaches adjust the structure, particle size, and particle size distribution of secondary particles in an attempt to improve the dispersion of lithium-rich cathode materials in cathode slurries and shorten the lithium ion transport distance, thereby enhancing the rate performance of lithium-rich cathode materials. Examples include patents CN106340638A, US9478808B2, and US10978709B2. While these approaches offer some potential for improving rate performance, further advancements are needed to further enhance the rate performance of lithium-rich cathode materials.

[0006] Summary of the Invention

[0007] The positive electrode material provided in this application, by limiting the relationship between the Dv50, average porosity and lithium richness of the positive electrode material, enables the lithium-ion battery prepared by the positive electrode material to have excellent specific capacity, energy density, rate performance and cycle performance, especially maintaining excellent electrochemical performance at high voltage.

[0008] The present application also provides a method for preparing a positive electrode material. The positive electrode material prepared by this method is applied to a lithium-ion battery, and the lithium-ion battery has excellent specific capacity, rate performance and cycle performance.

[0009] The present application also provides a positive electrode sheet, which includes the above-mentioned positive electrode material. Therefore, a lithium-ion battery assembled from the positive electrode sheet has excellent specific capacity, energy density, rate performance and cycle performance.

[0010] The present application also provides a lithium-ion battery, which includes the above-mentioned positive electrode sheet. Therefore, the lithium-ion battery assembled from the positive electrode sheet has excellent specific capacity, rate performance and cycle performance.

[0011] In a first aspect of the present application, a positive electrode material is provided, wherein the Dv50 value of the positive electrode material is α, and the unit is μm; the lithium richness of the positive electrode material is γ; the average porosity of the positive electrode material is expressed as a percentage as β%, wherein α, β, and γ satisfy: δ = β - [2α + 75γ] / 3, wherein 0≤δ≤4.0.

[0012] The positive electrode material as described above, wherein the positive electrode material comprises secondary particles and a coating layer covering at least a portion of the surface of the secondary particles.

[0013] The positive electrode material as described above, wherein the total molar amount of elements distributed in the secondary particles in the form of cations is A, the total molar amount of elements distributed in the secondary particles in the form of anions is B, and A and B satisfy: 0.985≤A / B≤1.0.

[0014] The positive electrode material as described above, wherein the secondary particles contain doped metal elements distributed in the form of cations and doped non-metallic elements distributed in the form of anions;

[0015] wherein the molar ratio of the doping metal element to the elements distributed in the secondary particles in the form of cations other than lithium ions is not higher than 5%; and / or,

[0016] The molar ratio of the doping non-metallic element to the total amount of elements distributed in the secondary particles in the form of anions is no more than 10%.

[0017] The positive electrode material as described above, wherein the chemical formula of the secondary particles is Li 1+x-2y M z M' 1-x-z O 2-y-t R t , where M is Ni a Co b Mn c , a+b+c=1.0, 0≤b≤0.10, a≥2b, 1.5≤c / (a+b)≤3.0, x=(ca) / (2+ca), 0.985≤(2-2y) / (2-y)≤1.0, (19-19x) / 20≤z≤(1-x), 0≤t≤(2-y) / 10;

[0018] Wherein, M' is a doping metal element, and R is a doping non-metal element.

[0019] The positive electrode material as described above, wherein the M' comprises at least one of Cr, Mo, W, Ta, Nb, P, Sb, Te, Hf, Ce, Ti, Zr, Sn, La, Al, Mg, Fe, K, and Na; and / or,

[0020] R includes at least one of F and S.

[0021] The positive electrode material as described above, wherein the Dv50 of the positive electrode material is 2.5 to 10.6 μm; and / or

[0022] The minimum particle size Dv of the positive electrode material min not less than 0.6 μm; and / or,

[0023] The secondary particles are formed by agglomeration of primary particles, and the average thickness of the primary particles is 80 to 250 nm; and / or,

[0024] The specific surface area of ​​the secondary particles is not less than 0.5 m 2 / g, and not higher than 1.5m 2 / g; and / or,

[0025] β is 7 to 13; and / or,

[0026] The lithium richness γ is 0.09 to 0.21.

[0027] The positive electrode material as described above, wherein the ratio of the molar amount of the coating layer material to the total molar amount of the positive electrode material is (0.2-1.0):100; and / or,

[0028] The coating layer material is phosphate and / or inert oxide; the phosphate includes at least one of AlPO4 and LaPO4, and the inert oxide includes at least one of Al2O3, TiO2, ZrO2, and La2O3.

[0029] A second aspect of the present application provides a method for preparing the positive electrode material according to the first aspect, comprising the following steps:

[0030] A metal salt solution, an alkaline solution, and an oxidant are mixed to obtain a reaction system, and a precipitation reaction is performed in the reaction system to obtain a precursor; wherein the oxidant comprises sodium hypochlorite, and the concentration of the oxidant in the reaction system is 0.2 to 2 g / L;

[0031] A precursor, a lithium salt, and a pore-forming agent are mixed to obtain a first mixed material, and the first mixed material is subjected to a first sintering treatment to obtain a positive electrode material.

[0032] The preparation method as described above, wherein the first mixed material further comprises a compound containing a doping element; and / or,

[0033] After the first sintering process, the method further includes: mixing the first sintering process product with the coating layer material to obtain a second mixture; and performing a second sintering process on the second mixture to obtain a positive electrode material.

[0034] The preparation method as described above, wherein the conditions of the precipitation reaction are: stirring speed 700-800 rpm, temperature 50-70° C., pH 9.5-11.5;

[0035] The temperature of the first sintering treatment is 800-950° C. and the holding time is 10-15 hours; and / or,

[0036] The coating layer material includes an inert oxide, the second sintering treatment is performed at a temperature of 500 to 800° C., a heating rate of 5 to 10° C. / min, and a time of 5 to 10 hours; and / or,

[0037] The coating layer material includes phosphate, the temperature of the second sintering treatment is 700-900° C., the heating rate is 5-10° C. / min, and the time is 5-10 hours.

[0038] The preparation method as described above, wherein the mass of the pore-forming agent is 0.1 to 1.0 wt% of the mass of the precursor;

[0039] The pore-forming agent includes at least one of ammonium carbonate, ammonium sulfate, ammonium persulfate, ammonium nitrate, and ammonium chloride.

[0040] In a third aspect of the present application, a positive electrode sheet is provided, which comprises the positive electrode material described in the first aspect or the positive electrode material prepared by the preparation method described in the second aspect.

[0041] The positive electrode sheet as described above, wherein the positive electrode sheet comprises a current collector and a positive electrode active material layer located on at least one functional surface of the current collector;

[0042] The positive electrode active material layer comprises the positive electrode material, a conductive agent, and a binder, wherein the mass ratio of the positive electrode material to the total mass ratio of the positive electrode active material layer is not less than 94 wt %.

[0043] A fourth aspect of the present application provides a lithium-ion battery, comprising the positive electrode sheet according to the third aspect.

[0044] The lithium-ion battery as described above, wherein the lithium-ion battery further comprises a separator, a negative electrode sheet and an electrolyte;

[0045] The negative electrode sheet is selected from at least one of lithium sheet, graphite, and silicon-carbon negative electrode.

[0046] The lithium-ion battery as described above, wherein after the lithium-ion battery is cycled for 200 cycles under the charge and discharge conditions of 2.5-4.5V and 0.5C / 1.0C, the growth rate of the cross-sectional average porosity of the positive electrode material on the positive electrode sheet is less than 2%.

[0047] In a fifth aspect of the present application, an electrical device is provided, comprising the lithium-ion battery described in the fourth aspect. Preferably, the electrical device comprises an electric car, a manned electric aircraft, or a drone.

[0048] The implementation of this application has at least the following beneficial effects:

[0049] The positive electrode material of the lithium-ion battery provided in the present application controls the Dv50 value α, lithium richness γ, and average porosity β% of the positive electrode material, satisfies δ=β-[2α+75γ] / 3, and 0≤δ≤4.0, thereby ensuring that the average particle size, lithium richness, and average porosity of the positive electrode material match each other, thereby maximizing the specific capacity, rate performance, and cycle performance of the lithium-ion battery prepared with the positive electrode material, especially the electrochemical performance under high voltage conditions.

[0050] The preparation method of the positive electrode material provided in the present application is beneficial to regulating the Dv50 value and average porosity of the positive electrode material by introducing an oxidant and a pore-forming agent and limiting the concentration of the oxidant. A positive electrode material satisfying the relationship δ = β - [2α + 75γ] / 3 can be prepared. The positive electrode material is applied to a lithium-ion battery, and the lithium-ion battery has excellent specific capacity, rate performance and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] FIG1 is a cross-sectional SEM image of the positive electrode material in Example 1 at a first magnification;

[0052] FIG2 is a cross-sectional SEM image of the positive electrode material in Example 1 at a second magnification;

[0053] FIG3 is a cross-sectional view and regional division diagram of the porosity measurement of a single secondary particle of the positive electrode material in Example 1;

[0054] FIG4 is a cross-sectional SEM image of the positive electrode material in Comparative Example 1 at a first magnification;

[0055] FIG5 is a cross-sectional SEM image of the positive electrode material in Comparative Example 1 at a second magnification;

[0056] FIG6 is a cross-sectional view and regional division diagram of the porosity measurement of a single secondary particle of the positive electrode material in Comparative Example 1;

[0057] FIG7 is a cross-sectional SEM image of the positive electrode material in Example 2 at a first magnification;

[0058] FIG8 is a cross-sectional SEM image of the positive electrode material in Example 2 at a second magnification;

[0059] FIG9 is a cross-sectional view and regional division diagram of the porosity measurement of a single secondary particle of the positive electrode material in Example 2;

[0060] FIG10 is a cross-sectional SEM image of the positive electrode material in Comparative Example 2 at a first magnification;

[0061] FIG11 is a cross-sectional SEM image of the positive electrode material in Comparative Example 2 at a second magnification;

[0062] FIG12 is a cross-sectional view and regional division diagram of the porosity measurement of a single secondary particle of the positive electrode material in Comparative Example 2;

[0063] FIG13 is a cross-sectional SEM image of the positive electrode material in Comparative Example 3 at a first magnification;

[0064] FIG14 is a cross-sectional SEM image of the positive electrode material in Comparative Example 3 at a second magnification;

[0065] FIG15 is a cross-sectional view and regional division diagram of the porosity measurement of a single secondary particle of the positive electrode material in Comparative Example 3;

[0066] FIG16 is a cross-sectional SEM image of the positive electrode sheet of a full battery assembled with the positive electrode material of Example 2 after 200 cycles at the first magnification;

[0067] FIG17 is a cross-sectional SEM image of the positive electrode sheet of a full battery assembled with the positive electrode material of Example 2 after 200 cycles at a second magnification;

[0068] FIG18 is a cross-sectional view and regional division diagram of the porosity measurement of a single secondary particle in the positive electrode material of a full battery assembled with the positive electrode material of Example 2 after 200 cycles;

[0069] FIG19 is a cross-sectional SEM image of the positive electrode sheet of a full battery assembled with the positive electrode material of Comparative Example 3 after 200 cycles at the first magnification;

[0070] FIG20 is a cross-sectional SEM image of the positive electrode sheet of a full battery assembled with the positive electrode material of Comparative Example 3 after 200 cycles at a second magnification;

[0071] Figure 21 is a cross-sectional view and regional division diagram of the porosity measurement of a single secondary particle in the positive electrode material after 200 cycles of the full battery assembled from the positive electrode material of Comparative Example 3. DETAILED DESCRIPTION

[0072] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0073] In a first aspect of the present application, a positive electrode material is provided, wherein the Dv50 value of the positive electrode material is α, in units of μm; the lithium richness of the positive electrode material is γ; the average porosity of the positive electrode material is expressed as a percentage as β%, wherein α, β, and γ satisfy: δ = β - [2α + 75γ] / 3, wherein 0≤δ≤4.0.

[0074] In this application, the Dv50 of a positive electrode material refers to the particle size corresponding to 50% of the volume distribution of the particles constituting the positive electrode material, also known as the average particle size. The lithium-rich content refers to a positive electrode material having a lithium:transition metal ratio greater than 1. In other words, within a positive electrode material having a specific chemical formula, the portion of the positive electrode material where the lithium subscript exceeds 1 is the lithium-rich content. The average porosity of a positive electrode material refers to the percentage of the volume of pores within the particles constituting the positive electrode material to the volume of the positive electrode material. When the positive electrode material is composed of secondary particles, the average porosity of the positive electrode material is specifically measured by calculating the porosity of a single secondary particle of the positive electrode material and taking the average porosity of 20 or more secondary particles in the positive electrode material to obtain the average porosity of the positive electrode material.

[0075] The present application does not impose too many restrictions on the specific type of positive electrode material, for example, it can be a lithium-rich positive electrode material. In a lithium-ion battery prepared with a lithium-rich positive electrode material, a part of the battery's specific capacity is provided by the anion redox process.

[0076] The inventors believe that the average porosity of the positive electrode material has an extremely significant impact on the rate performance of the positive electrode material (especially the lithium-rich positive electrode material). The appropriate average porosity is the key to the excellent rate performance of the lithium-rich material, and the average porosity should be controlled within a reasonable range. If the average porosity of the positive electrode material is too high, the structural strength and compaction density of the positive electrode material will decrease. In addition, in the early stage of the cycle of the positive electrode material, the electrolyte will not completely penetrate into the interior of the positive electrode material. The excessively high porosity will easily form local "islands" inside the positive electrode material, which is not conducive to power performance and capacity. As the cycle progresses, more electrolyte contacts the positive electrode material, which in turn triggers serious side reactions, reduces the stability of the battery, increases gas production, and is not conducive to industrial application. If the average porosity of the positive electrode material is too low, the tortuosity of the lithium ion transmission path is high, and the electrolyte infiltration effect is poor, which will seriously affect the rate performance.

[0077] The ternary cathode materials in the prior art have excellent rate performance, so there is no need to adjust the porosity of the cathode materials according to the particle size and transition metal ratio. Taking into account the particle strength and volume energy density, the porosity of the secondary particles in the ternary cathode materials usually needs to be controlled within 3%. In the relationship formula δ = β - [2α + 75γ] / 3 of the present application, the average porosity value of the cathode material is positively correlated with the lithium richness and Dv50 values. That is, when the lithium richness of the cathode material is higher, the corresponding average porosity of the cathode material is higher; when the Dv50 of the cathode material is higher, the corresponding average porosity of the cathode material is higher.

[0078] In addition, in the prior art, the porosity of lithium-rich positive electrode materials varies greatly, making it difficult to achieve comprehensive consideration and design of power characteristics (rate performance), capacity utilization, structural stability, and energy density. There are phenomena where the capacity utilization is high but the porosity is too high, the power performance is acceptable but the compaction density does not meet the standard, or the compaction density is high and the porosity is low, but the capacity utilization does not meet the standard and the power performance is poor. However, the present application can improve the rate performance, capacity utilization, structural stability, and energy density of batteries including the above-mentioned positive electrode materials by limiting the relationship between the average porosity value and the lithium richness and Dv50 value. This is because:

[0079] On the one hand, the lithium richness in the positive electrode material is directly related to the ratio of nickel and manganese transition metal elements in the positive electrode material, and the lithium richness in the positive electrode material can characterize the proportion of lithium-rich phase, that is, the proportion of anions in the positive electrode material used for oxidation and reduction to provide capacity. When the lithium richness is higher, the proportion of anion redox contribution to capacity in the positive electrode material is higher. Correspondingly, the cell parameter changes more widely, and the kinetic performance tends to deteriorate. At this time, the average porosity value of the positive electrode material specified in the present application is positively correlated with the lithium richness value, which means that the positive electrode material of the present application has a correspondingly large average porosity value, so that the positive electrode material is in full contact with the electrolyte, optimizes the lithium ion transmission path, offsets the kinetic performance loss of the positive electrode material due to the increased degree of anion redox, and keeps the kinetic performance at a high level, thereby ensuring the energy density of the positive electrode sheet and the specific capacity and rate performance of the lithium-ion battery.

[0080] On the other hand, the Dv50 of the positive electrode material directly affects the kinetic performance of the positive electrode material. The larger the Dv50, the longer the lithium ion transmission distance. In addition, the volume shrinkage and expansion of the positive electrode material particles during the charging and discharging process will cause the particles to squeeze each other, and there is a tendency to form greater internal stress and more grain boundaries, which is not conducive to the continuous migration of lithium ions. At this time, the average porosity value of the positive electrode material specified in the present application is positively correlated with the Dv50 value as mentioned above, which means that the positive electrode material of the present application has a relatively large average porosity value, which can reduce internal stress, avoid secondary particle fragmentation, and protect lithium ions from migration difficulties caused by increased stress, offsetting the intensified polarization of the positive electrode material due to the increase in lithium ion transmission distance, thereby ensuring the cycle performance and rate performance of the lithium-ion battery.

[0081] When the positive electrode material of the present application is a layered lithium-rich positive electrode material, the positive electrode material is a layered structure. At this time, in some embodiments, the positive electrode material includes secondary particles and a coating layer covering at least part of the surface of the secondary particles. Among them, the secondary particles are obtained by aggregating a plurality of primary particles, and the secondary particles have a spherical or approximately spherical shape, such as an ellipsoidal shape. The coating layer can reduce the side reaction between the positive electrode material and the electrolyte, inhibit the degradation of the surface structure of the positive electrode material, the dissolution of transition metals in the secondary particles, and the deactivation of the electrolyte, thereby improving the stability of the positive electrode material, and especially ensuring the stability of the positive electrode material in a high voltage system.

[0082] In the prior art, the ratio of the sum of anions to the sum of cations in ternary positive electrode materials is 1. However, for lithium-rich positive electrode materials, the surface structure may change during the coating process. The corrosive effect of some acidic substances will cause the surface of the secondary particles to release Li2O, resulting in a ratio of the sum of anions to the sum of cations less than 1. However, excessive release of Li2O will cause the structure of the positive electrode material to collapse, resulting in a significant decrease in the capacity and stability of the battery. Therefore, in some embodiments, the total molar amount of elements distributed in the form of cations in the secondary particles is A, and the total molar amount of elements distributed in the form of anions in the secondary particles is B. A and B satisfy: 0.985≤A / B≤1.0, that is, the lithium ion release ratio is limited to no more than 6%, ensuring that the coating layer improves the interface stability of the positive electrode material while not destroying the bulk structural stability of the secondary particles.

[0083] Taking layered lithium-rich cathode materials as an example, in addition to Li, Ni, Co, and Mn, other metal elements distributed in the form of cations and non-metallic elements distributed in the form of cations can be doped to meet the diverse performance requirements of industrialization. In some embodiments, the secondary particles contain doping metal elements distributed in the form of cations and doping non-metallic elements distributed in the form of anions. The molar ratio of the doping metal elements to the elements distributed in the form of cations other than lithium ions in the secondary particles is no more than 5%. The elements distributed in the form of cations other than lithium ions in the secondary particles include Ni, Co, Mn, and the doping metal element. In this case, the molar amount of the doping metal element / the total molar amount of Ni, Co, Mn, and the doping metal element × 100% is ≤ 5%. Continuing with the example of layered lithium-rich cathode materials, in some embodiments, the molar ratio of the doping non-metallic element to the total molar amount of elements distributed in the form of anions in the secondary particles is no more than 10%. The sum of elements distributed in the secondary particles as anions includes O and doped non-metallic elements. In this case, the molar amount of the doped non-metallic element / O / total molar amount of the doped non-metallic elements × 100% is ≤ 10%. By limiting the amounts of doped metal elements and doped non-metallic elements, specific aspects of the cathode material's performance can be improved to varying degrees while also avoiding imbalances in product performance caused by excessive doping.

[0084] In this application, the chemical formula of the secondary particles is Li 1+x-2y M z M' 1-x-z O 2-y-t R t , where M is Ni a Co b Mn c , a+b+c=1.0, 0≤b≤0.10, a≥2b, 1.5≤c / (a+b)≤3.0, x=(ca) / (2+ca), 0.985≤(2-2y) / (2-y)≤1.0, (19-19x) / 20≤z≤(1-x), 0≤t≤(2-y) / 10; where M' is a doping metal element and R is a doping non-metal element

[0085] By limiting 0.985≤(2-2y) / (2-y)≤1.0, it is beneficial to achieve that the ratio of the total molar amount A of elements distributed in the secondary particles in the form of cations to the total molar amount B of elements distributed in the form of anions satisfies 0.985≤A / B≤1.0; by limiting (19-19x) / 20≤z≤(1-x), it is beneficial to achieve that the molar ratio of doped metal elements to other elements distributed in the form of cations other than lithium ions in the secondary particles is not higher than 5%; by limiting 0≤t≤(2-y) / 10, it is beneficial to achieve that the molar amount of doped non-metallic elements / O and the total molar amount of doped non-metallic elements×100%≤10%.

[0086] In the chemical formula of the above-mentioned secondary particles, the lithium-rich amount γ of the positive electrode material can be x-2y. By limiting x=(ca) / (2+ca), at this time, the lithium-rich amount is directly related to the molar ratio of nickel and manganese elements, that is, the lithium ratio of the positive electrode material is directly related to the ratio of transition metal elements, and appropriate lithium matching can ensure that the material can exert maximum electrochemical performance. Specifically, the lithium content is adjusted according to the relative molar amount of nickel and manganese elements so that all elements distributed in the form of cations are in a stable valence, especially the valence state of the Mn element is closer to +4, and the influence of the Jahn-Teller effect on the structural stability is reduced as much as possible, so that the performance of the positive electrode material is in the optimal range. If the lithium ratio is too high, it will easily lead to excessive growth of the positive electrode material particles, the activity of Li2MnO3 in the positive electrode material will be seriously reduced, and the valence of the nickel element will be increased, resulting in a decrease in power performance and limited capacity. The positive electrode material provided in the present application satisfies the above relationship and has a reasonable lithium-rich amount, which can keep the rate performance, capacity play and cycle stability of the positive electrode material at the maximum level.

[0087] The addition of nickel increases the energy density of lithium-ion batteries. The addition of cobalt stabilizes the layered structure of the cathode material, improving the cycle life and rate performance of the resulting lithium-ion battery while minimizing the impact on the specific capacity of the battery. The addition of manganese not only improves the structural stability of the cathode material and the safety of the resulting lithium-ion battery, but also reduces the material cost of the battery while minimizing the impact on the specific capacity. Therefore, by carefully selecting the composition ratio of nickel, cobalt, and manganese in the secondary particles of the cathode material, the energy density, cycle performance, and rate performance of the lithium-ion battery produced from the cathode material can be balanced.

[0088] When 0≤b≤0.10 and a≥2b are satisfied, the molar proportion of nickel element is higher than 2 times the molar proportion of cobalt element, and the molar proportion of cobalt element is not higher than 10%. On the one hand, controlling the proportion of cobalt element can reduce material cost. On the other hand, compared with nickel element, increasing the cobalt element content can slightly improve the capacity of the positive electrode material. But at the same time, since the upper limit of the application voltage window of layered lithium-rich positive electrode material is higher than that of ternary positive electrode material, the main reason for the capacity improvement brought by cobalt element in layered lithium-rich positive electrode material is that cobalt can catalyze and increase the activity of lithium-rich phase. Therefore, the increase in cobalt element content will cause the structural stability of the layered lithium-rich positive electrode material to decrease slightly due to the higher amplitude of anion redox. Similarly, the power performance will also decrease slightly. The cycle stability of the layered lithium-rich positive electrode material of the cobalt-free system is not lower than that of the layered lithium-rich positive electrode material of the cobalt-containing system, but due to the lack of catalytic activation of cobalt, the initial polarization of the positive electrode material is large, and Li2MnO3 will be continuously activated in the early stage of the cycle, resulting in the disadvantage of continuous increase in the overall capacity of the positive electrode material, which poses a challenge to the BMS design of the battery cell. This application can avoid this phenomenon by controlling the cobalt content and reduce the cost of later design. Therefore, the above-mentioned positive electrode material provided by this application can effectively balance the above pros and cons. By limiting the proportion of transition metals, it balances the key indicators of the cost, rate performance, capacity performance, structural stability and other key indicators of the positive electrode material to ensure the excellent comprehensive performance of the positive electrode material, so that the positive electrode material is more in line with the performance requirements of industrialization.

[0089] When 1.5≤c / (a+b)≤3.0 is satisfied, the molar fraction of manganese is no less than 1.5 times the sum of the molar fractions of nickel and manganese, ensuring the cathode material's watt-hour cost is lower than that of other ternary cathode materials. Furthermore, the molar fraction of manganese is no more than 3 times the sum of the molar fractions of nickel and manganese, which limits the upper limit of the lithium-rich phase in the cathode material. In practical applications, capacity is not directly proportional to the proportion of the lithium-rich phase. When the proportion of the lithium-rich phase reaches a certain limit, further increases in its proportion significantly slow the capacity gain due to increased material polarization, and even lead to capacity reduction in high-density systems. Furthermore, manganese is prone to disproportionation reactions during long cycles and dissolves into the electrolyte. Under the influence of the electric field, it migrates to the negative electrode, causing negative electrode deactivation. Furthermore, an excessively high molar fraction of manganese, i.e., an excessively high proportion of the lithium-rich phase, reduces the structural stability of the cathode material. Batteries assembled with this cathode material experience rapid energy decay, failing to meet industrial demand. Therefore, when 1.5≤c / (a+b)≤3.0 is satisfied, the battery system can have a higher cost-effectiveness.

[0090] The present application does not limit the specific types of the aforementioned doping metal elements M' and non-metallic elements R, and these may be adjusted based on actual needs. For example, in some embodiments, M' includes at least one of Cr, Mo, W, Ta, Nb, P, Sb, Te, Hf, Ce, Ti, Zr, Sn, La, Al, Mg, Fe, K, and Na; and / or R includes at least one of F and S.

[0091] Specifically, the above-mentioned doping metal element can be Cr 6+ 、Mo 6+ 、W 6+ 、Ta 5+ 、Nb 5+ 、P 5+ 、Sb 5+ 、Te 4+ , Hf 4+ 、Ce 4+ 、Ti 4+ 、Zr 4+ 、Sn 4+ 、La 3+ 、Al 3+ Mg 2+ 、Fe 2+ , K + 、Na + The above-mentioned doped non-metallic elements can be distributed in the secondary particles in the form of F - 、S 2- The morphology is distributed in the secondary particles.

[0092] Among them, when the doping metal elements are Mo, W, Ta, Nb, Sb, Mo6+ 、W 6+ 、Ta 5+ 、Nb 5+ 、Sb 5+ The distribution of high-valent cation forms helps to control the particle size of the primary particles of the positive electrode material. With the increase of the concentration of the doping element in the form of high-valent cations, under the same sintering conditions, the particle size of the primary particles of the positive electrode material becomes smaller, the internal stress becomes smaller, the capacity will be improved, and the secondary particles will not be easily cracked as the cycle progresses, which is beneficial to improving the cycle performance and safety performance. When the doping metal element is P, P 5+ It tends to form phosphate in the subsurface of the positive electrode material (that is, the surface of the secondary particles), which improves the stability of the anion framework and prolongs the service life of the positive electrode material. When the doped metal elements are Cr, Te, Hf, Ti, Zr, Sn, La, Al, Mg, Fe, K, and Na, Cr 6+ 、Te 4+ , Hf 4+ 、Ti 4+ 、Zr 4+ 、Sn 4+ 、La 3+ 、Al 3+ Mg 2+ 、Fe 2+ , K + 、Na + It can increase the stability of the alkali metal layer (i.e. lithium layer) or the transition metal layer (i.e. nickel, cobalt and manganese layer), inhibit irreversible cation migration, and stabilize the bulk structure; when the doped non-metallic element is F, F - It has stronger electronegativity and can form stronger covalent bonds with cations, thereby improving the structural stability of the positive electrode material. When the doped non-metallic element is S, S 2- Doping can stabilize the anion framework, S 2- To a certain extent, it acts as a buffer site for the redox of oxygen anions, improving the reversibility of oxygen anion redox, which is beneficial to the improvement of capacity and rate performance.

[0093] In some embodiments, the Dv50 of the positive electrode material is 2.5 to 10.6 μm; and / or the minimum particle size Dv min The thickness of the positive electrode material is not less than 0.6 μm, so as to control the absence of fine powder in the positive electrode material, avoid serious interface side reactions and cyclic gas production, and improve the cycle performance and safety performance of the battery assembled by the positive electrode sheet. To further improve the safety performance of the battery, in some embodiments, the secondary particles are formed by the agglomeration of primary particles, and the average thickness of the primary particles is 80 to 250 nm; the specific surface area of ​​the secondary particles is not less than 0.5 m 2 / g, and not higher than 1.5m 2By limiting the average thickness of the primary particles and the specific surface area of ​​the secondary particles, the contact area between the positive electrode material and the electrolyte can be limited and sufficient to fully exert the power performance.

[0094] The existing technology tends to improve the capacity and efficiency of lithium-rich cathode materials by surface acid corrosion and other means. For example, a layer of spinel structure is formed on the surface of the cathode material to improve the surface lithium ion conductivity. However, after such treatment, many fresh interfaces will be formed on the cathode material, and the gaps between particles will also increase significantly. Therefore, the specific surface area is usually around 2.0m 2 / g or above, even 3.0m 2 / g or more, the increase in specific surface area and fresh interface will inevitably lead to the intensification of interface side reactions. The specific surface area of ​​the secondary particles of this application is not less than 0.5m 2 / g, and not higher than 1.5m 2 / g, ensuring that the positive electrode material has specific pores, guaranteeing the power performance and capacity of the positive electrode material, and thus enabling the performance of the positive electrode material to be fully exerted.

[0095] In the prior art, compared with ternary positive electrode materials, the lattice stress of lithium-rich positive electrode materials is greater during the point chemical reaction, and the kinetic performance tends to be slightly lower. In the positive electrode material of the present application, the average thickness of the primary particles is 80 to 250 nm, which ensures that the internal stress of the single particles is low, so that lithium ions can be smoothly embedded and removed, so that the performance of the positive electrode material can be fully exerted. If the average thickness of the primary particles is greater than 250 nm, it will lead to kinetic problems caused by excessive thickness, thereby affecting the power performance and capacity. If the average thickness of the primary particles is less than 80 nm, the compaction density and particle strength caused by excessive thinness will drop rapidly, and the specific surface area will increase significantly.

[0096] The present application does not limit the specific values ​​of the lithium-rich content γ and the average porosity β% of the positive electrode material, as long as the above relationship is satisfied. For example, in some embodiments, β is 7 to 13; and / or the lithium-rich content γ is 0.09 to 0.21.

[0097] The present application does not limit the specific material and size of the coating layer. For example, in some embodiments, the thickness of the coating layer is 2 to 10 nm; and / or the total molar amount of the coating layer material and the total molar amount of the positive electrode material are in a ratio of (0.2 to 1.0):100; and / or the coating layer material is phosphate and / or inert oxide; the phosphate includes at least one of AlPO4 and LiNiPO4, and the inert oxide includes at least one of Al2O3, TiO2, ZrO2, and La2O3. By coating with the above-mentioned inert oxide or / and phosphate coating layer, the positive electrode material can be adapted to a high voltage window. Compared with the ternary positive electrode material, the positive electrode material of the present application can maintain higher stability in a higher voltage window to meet industrialization requirements.

[0098] In a second aspect of the present application, a method for preparing the positive electrode material provided in the first aspect is provided, comprising the following steps:

[0099] A metal salt solution, an alkaline solution, and an oxidant are mixed to obtain a reaction system, and a precipitation reaction is performed in the reaction system to obtain a precursor; wherein the oxidant includes sodium hypochlorite, and the concentration of sodium hypochlorite in the reaction system is 0.2 to 2 g / L;

[0100] The precursor, lithium salt and pore-forming agent are mixed to obtain a first mixed material, and the first mixed material is subjected to a first sintering treatment to obtain a positive electrode material.

[0101] The metal salt solution may be a metal sulfate solution, and the concentration of the metal sulfate is 2 to 3 mol / L; the alkaline solution may be sodium hydroxide, and the concentration of the sodium hydroxide is 5 to 10 mol / L.

[0102] In the prior art, in the precursor synthesis process of the ternary positive electrode material, the oxygen content is required to be extremely low, otherwise it will cause the morphology of the precursor to be irregular and agglomerated, the crystal structure to change, and the appearance of a heterogeneous phase. The inventor believes that the concentration of the oxidant will directly affect the density of the precursor, thereby affecting the porosity of the positive electrode material. This is because the concentration of the oxidant affects the kinetic characteristics of the precipitation reaction. The present application adjusts the concentration of the oxidant to oxidize some elements in the reaction system, so that some elements nucleate and grow separately, and restricts the transition metal from continuing to bind and grow on the surface of the original primary particles to make the thickness of the primary particles too thick, so as to regulate the density of the precursor and control the particle size and porosity of the secondary particles formed subsequently, thereby facilitating the regulation of the Dv50 value and the average porosity of the final positive electrode material.

[0103] It should be noted that the sodium hypochlorite concentration is negatively correlated with the target secondary particle size. That is, the higher the sodium hypochlorite concentration, the smaller the target secondary particle size; the lower the sodium hypochlorite concentration, the larger the target secondary particle size. The sodium hypochlorite concentration is positively correlated with the atomic ratio of manganese in the precursor. This is because: the higher the manganese ratio, the higher the proportion of manganese-rich phase in the final positive electrode material. Therefore, the porosity needs to be increased, that is, the amount of sodium hypochlorite needs to be increased accordingly. Therefore, the sodium hypochlorite concentration is positively correlated with the manganese ratio. That is, as the manganese ratio in the nickel-cobalt-manganese element increases, the amount of sodium hypochlorite needs to be increased accordingly.

[0104] The present application further controls the average porosity of the target cathode material by utilizing a pore-forming agent. The precursor, lithium salt, compound containing a doping element, and pore-forming agent are fully mixed and then subjected to a first sintering treatment. During the first sintering treatment, the pore-forming agent begins to decompose and generate gas below 400°C, before or during the lithiation of the oxide produced by the decomposition of the hydroxide precursor into an ordered layered lithium-rich cathode material. Therefore, during the lithiation of the transition metal oxide into a lithium-rich cathode material, the pore-forming agent continuously releases a certain amount of gas to achieve the purpose of preparing a cathode material with a specific average porosity. The above-mentioned method provided in the present application can achieve highly controllable average porosity of the cathode material, and accordingly, its power performance can be maximized. At the same time, sufficient unit cell "breathing" space can effectively improve the stability of the crystal structure, ensure the structural strength of the secondary particles, reduce the volume change rate and porosity change rate of the secondary particles, extend the long cycle life of the cathode material in the battery, and provide a guarantee for stable use in large-scale battery cells.

[0105] In some embodiments, the first mixed material further includes a compound containing a doping element to form a coating layer during the second sintering process. The compound containing a doping element includes compounds containing doped metal elements and compounds containing doped non-metallic elements. And / or, after the first sintering process, the process further includes: mixing the first sintering product with a coating layer material to obtain a second mixture; and performing a second sintering process on the second mixture to obtain a positive electrode material. The second sintering process forms a coating layer on the surface of the secondary particles, reducing side reactions between the positive electrode material and the electrolyte, thereby improving the stability of the battery system.

[0106] This application does not impose too many restrictions on the parameters of the above-mentioned preparation process. For example, in some embodiments, the conditions of the precipitation reaction are: stirring speed 700-800 rpm, temperature 50-70°C, pH 9.5-11.5; the temperature of the first sintering treatment is 800-950°C, and the insulation time is 10-15h.

[0107] When the coating material consists solely of an inert oxide, the second sintering process is performed at a temperature of 500-800°C, a heating rate of 5-10°C / min, and a duration of 5-10 hours. When the coating material consists solely of a phosphate, the second sintering process is performed at a temperature of 700-900°C, a heating rate of 5-10°C / min, and a duration of 5-10 hours. The first sintering process is performed in an air atmosphere. When the coating material consists of both an inert oxide and a phosphate, the second sintering process is performed at a temperature of 700-800°C, a heating rate of 5-10°C / min, and a duration of 5-10 hours.

[0108] The present application does not limit the specific type and addition amount of the pore-forming agent. The pore-forming agent can be an ammonium salt of a coordinated polyanion that can be vaporized by heat. For example, in some embodiments, the mass of the pore-forming agent is 0.1 to 1.0 wt% of the mass of the precursor; the pore-forming agent includes at least one of ammonium carbonate, ammonium sulfate, ammonium persulfate, ammonium nitrate, and ammonium chloride.

[0109] It should be noted that during the above preparation process, an excess of lithium is typically added. That is, in addition to satisfying the molar ratio of lithium in the chemical formula, an additional 3 to 5 at% of lithium is added to avoid lithium loss during the preparation process. In the specific implementation of this application, the actual molar amount of lithium salt / the theoretical molar amount of lithium = 1.03 to 1.05, where the theoretical molar amount of lithium is the amount of lithium salt added to satisfy the chemical formula.

[0110] In a third aspect of the present application, a positive electrode sheet is provided, which includes the positive electrode material of the first aspect or the positive electrode material prepared by the preparation method of the second aspect.

[0111] In some embodiments, the positive electrode sheet includes a current collector and a positive electrode active material layer located on at least one functional surface of the current collector; the positive electrode active material layer includes a positive electrode material, a conductive agent, and a binder. The positive electrode material accounts for no less than 94 wt % of the total mass of the positive electrode active material layer.

[0112] The positive electrode sheet of the present application can also be prepared by conventional technical means in the field. Specifically, the above-mentioned positive electrode material, conductive agent, and binder can be uniformly dispersed in a solvent to obtain a positive electrode active layer slurry, and then the positive electrode active layer slurry is coated on at least one functional surface of the positive electrode current collector. After drying, the positive electrode sheet of the present application can be obtained.

[0113] The present application does not particularly limit the specific categories of the conductive agent and the adhesive. The conductive agent, the adhesive and other components can be selected from conventional substances in the field. For example, the conductive agent can be selected from one or more of conductive carbon black, carbon nanotubes, conductive graphite, and graphene, and the adhesive can be selected from one or more of polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymers, polyimide, styrene-butadiene rubber, and styrene-propylene rubber.

[0114] The present application does not specifically limit the coating method, and the positive electrode active layer slurry can be coated by any coating method such as gravure coating, extrusion coating, spraying, screen printing, etc.

[0115] In a fourth aspect of the present application, a lithium-ion battery is provided, wherein the lithium-ion battery includes the positive electrode sheet provided in the third aspect.

[0116] In addition to the positive electrode, the lithium-ion battery of the present application, in some embodiments, also includes a separator, a negative electrode, and an electrolyte. The composition of the negative electrode can refer to conventional negative electrode sheets in the art, and the separator can also be a conventional separator in the art, such as PP film or PE film. The negative electrode is selected from at least one of a lithium sheet, graphite, and a silicon-carbon negative electrode.

[0117] The lithium-ion battery of the present application can be prepared by conventional methods in the field. Specifically, the positive electrode sheet, the separator and the negative electrode sheet can be stacked in sequence, and then the battery cell can be obtained through a lamination or winding process. Then, the battery cell can be obtained through baking, liquid injection, formation, packaging and other processes.

[0118] Taking the negative electrode sheet as a metal lithium sheet as an example, in some embodiments, after the lithium-ion battery is cycled for 200 cycles under the charge and discharge conditions of 2.5-4.55V and 0.5C / 1.0C, the growth rate of the average porosity of the cross section of the positive electrode material on the positive electrode sheet is less than 2%.

[0119] In a fifth aspect of the present application, an electrical device is provided, comprising the lithium-ion battery of the fourth aspect. Preferably, the electrical device comprises an electric car, a manned electric aircraft, or a drone.

[0120] The present application will be further described below through specific examples and comparative examples.

[0121] Example 1

[0122] (1) A metal salt solution is introduced into a reactor at a rate of 10 mL / min, a sodium hydroxide solution is introduced at a rate of 8.0±0.2 mL / min, and sodium hypochlorite is added at a rate of 0.009 g / min, with a stirring speed of 800 rpm, a temperature of 50°C, a pH of 10.6, and a reaction time to obtain a precursor with a qualified particle size of 6 to 8 μm; wherein the metal salt solution is a sulfate solution containing nickel and manganese (the molar ratio of nickel to manganese is 35:65), and the metal salt concentration is 2 mol / L; the sodium hydroxide concentration in the sodium hydroxide solution is 5 mol / L; and the sodium hypochlorite concentration in the reaction system is 0.5 g / L.

[0123] (2) Ni 0.35 Mn 0.65(OH)2, lithium salt Li2CO3, 1.0 mol and 0.67 mol (3 at% excess on the basis of 0.65 mol) were added, and ammonium sulfate was added (the mass of ammonium sulfate was 0.6% of the mass of the precursor) and mixed thoroughly to obtain a first mixture, which was subjected to a first sintering treatment in an air atmosphere at a temperature of 900°C for 12 hours, and then naturally cooled to room temperature to obtain a positive electrode material Li 1.13 Ni 0.305 Mn 0.565 O2.

[0124] Example 2

[0125] The preparation process is basically the same as that in Example 1, except that in step (1), "the concentration of sodium hypochlorite in the reaction system is 0.5 g / L" is replaced by "the concentration of sodium hypochlorite in the reaction system is 0.8 g / L", and other conditions remain unchanged to obtain a precursor; in step (2), the precursor of Example 1 is replaced by the precursor of this embodiment; "ammonium sulfate" is replaced by "ammonium carbonate"; "the mass of ammonium sulfate is 0.6% of the mass of the precursor" is replaced by "the mass of ammonium carbonate is 0.2% of the mass of the precursor", and other conditions remain unchanged to obtain a positive electrode material Li 1.131 Ni 0.302 Mn 0.567 O2.

[0126] Example 3

[0127] The preparation process is basically the same as that in Example 1, except that in step (1), "the concentration of sodium hypochlorite in the reaction system is 0.5 g / L" is replaced by "the concentration of sodium hypochlorite in the reaction system is 1.5 g / L", and other conditions remain unchanged to obtain a precursor; in step (2), the precursor of Example 1 is replaced by the precursor of this embodiment; "ammonium sulfate" is replaced by "ammonium nitrate"; "the mass of ammonium sulfate is 0.6% of the mass of the precursor" is replaced by "the mass of ammonium nitrate is 0.5% of the mass of the precursor", and other conditions remain unchanged to obtain a positive electrode material Li 1.13 Ni 0.308 Mn 0.562 O2.

[0128] Example 4

[0129] The preparation process is basically the same as that in Example 1, except that in step (1), "the metal salt solution is a sulfate solution containing nickel and manganese (nickel-manganese molar ratio is 35:65)" is replaced by "the metal salt solution is a sulfate solution containing nickel and manganese (nickel-manganese molar ratio is 25:75)"; "the sodium hypochlorite concentration in the reaction system is 0.5 g / L" is replaced by "the sodium hypochlorite concentration in the reaction system is 1.5 g / L", and other conditions remain unchanged to obtain a precursor; in step (2), the precursor of Example 1 is replaced by the precursor of this embodiment; "ammonium sulfate" is replaced by "ammonium carbonate"; "the mass of ammonium sulfate is 0.6% of the mass of the precursor" is replaced by "the mass of ammonium carbonate is 0.8% of the mass of the precursor", and other conditions remain unchanged to obtain the positive electrode material Li 1.203 Ni 0.2 Mn 0.597 O2.

[0130] Example 5

[0131] The preparation process is basically the same as that in Example 1, except that the "metal salt solution is a sulfate solution containing nickel and manganese (nickel-manganese molar ratio of 35:65)" in step (1) is replaced by "the metal salt solution is a sulfate solution containing nickel and manganese (nickel-manganese molar ratio of 40:60)"; "the sodium hypochlorite concentration in the reaction system is 0.5 g / L" is replaced by "the sodium hypochlorite concentration in the reaction system is 1.3 g / L", and other conditions remain unchanged to obtain a precursor; in step (2), the precursor of Example 1 is replaced by the precursor of this embodiment; "ammonium sulfate" is replaced by "ammonium chloride"; "the mass of ammonium sulfate is 0.6% of the mass of the precursor" is replaced by "the mass of ammonium chloride is 0.8% of the mass of the precursor", and other conditions remain unchanged to obtain the positive electrode material Li 1.091 Ni 0.365 Mn 0.544 O2.

[0132] Example 6

[0133] The preparation process is basically the same as that in Example 1, except that in step (1), "the metal salt solution is a sulfate solution containing nickel and manganese (nickel-manganese molar ratio is 35:65)" is replaced by "the metal salt solution is a sulfate solution containing nickel, cobalt and manganese (nickel, cobalt, manganese molar ratio is 30:10:60)"; "the sodium hypochlorite concentration in the reaction system is 0.5 g / L" is replaced by "the sodium hypochlorite concentration in the reaction system is 1.2 g / L", and other conditions remain unchanged to obtain a precursor; in step (2), the precursor of Example 1 is replaced by the precursor of this embodiment; "ammonium sulfate" is replaced by "ammonium persulfate"; "the mass of ammonium sulfate is 0.6% of the mass of the precursor" is replaced by "the mass of ammonium persulfate is 0.3% of the mass of the precursor", and other conditions remain unchanged to obtain the positive electrode material Li 1.313 Ni 0.262 Co0.087 Mn 0.52 O2.

[0134] Example 7

[0135] The preparation process is basically the same as that in Example 1, except that in step (1), "the concentration of sodium hypochlorite in the reaction system is 0.5 g / L" is replaced by "the concentration of sodium hypochlorite in the reaction system is 1.0 g / L", and other conditions remain unchanged to obtain a precursor; in step (2), the precursor of Example 1 is replaced by the precursor of this embodiment; "ammonium sulfate" is replaced by "ammonium chloride"; "the mass of ammonium sulfate is 0.6% of the mass of the precursor" is replaced by "the mass of ammonium chloride is 0.5% of the mass of the precursor", and compounds containing doping elements WO3, Nb2O5, Al2O3, and NH4H2PO4 are added to the first mixture, wherein the ratios of the atomic weights of the W, Nb, Al, and P elements to the atomic weight of the nickel element in the precursor are 1:29.2, 1:29.2, 1:29.2, and 1:29.2, respectively, and other conditions remain unchanged to obtain the positive electrode material Li 1.13 Ni 0.292 Mn 0.548 W 0.01 Nb 0.01 Al 0.01 P 0.01 O2.

[0136] Example 8

[0137] The preparation process is basically the same as that in Example 1, except that in step (1), "the concentration of sodium hypochlorite in the reaction system is 0.5 g / L" is replaced by "the concentration of sodium hypochlorite in the reaction system is 0.9 g / L", and other conditions remain unchanged to obtain a precursor; in step (2), the precursor of Example 1 is replaced by the precursor of this embodiment; "ammonium sulfate" is replaced by "ammonium nitrate"; "the mass of ammonium sulfate is 0.6% of the mass of the precursor" is replaced by "the mass of ammonium nitrate is 0.5% of the mass of the precursor", and compounds containing doping elements WO3, Nb2O5, Al2O3, and NH4H2PO4 are added to the first mixture, wherein the ratios of the atomic weights of the W, Nb, Al, and P elements to the atomic weight of the nickel element in the precursor are 1:29.2, 1:29.2, 1:29.2, and 1:29.2, respectively, and other conditions remain unchanged to obtain a first sintered product Li 1.13 Ni 0.292 Mn 0.548 W 0.01 Nb 0.01 Al 0.01 P 0.01 O2;

[0138] Add step (3): mix the first sintering treatment product with 0.03 mol% Al2O3 and 0.02 mol% TiO2 to obtain a second mixture; perform a second sintering treatment on the second mixture, sintering it at 550°C in an air atmosphere for 10 hours to obtain a lithium-rich positive electrode material 0.03Al2O3·0.02TiO2·Li ​​composite coated with Al2O3 and TiO2 1.13 Ni 0.292 Mn 0.548 W 0.01 Nb 0.01 Al 0.01 P 0.01 O2.

[0139] Example 9

[0140] The preparation process is basically the same as that of Example 1, except that in step (1), "the concentration of sodium hypochlorite in the reaction system is 0.5 g / L" is replaced by "the concentration of sodium hypochlorite in the reaction system is 0.9 g / L", and other conditions remain unchanged to obtain a precursor; in step (2), the precursor of Example 1 is replaced by the precursor of this embodiment; "ammonium sulfate" is replaced by "ammonium carbonate"; "the mass of ammonium sulfate is 0.6% of the mass of the precursor" is replaced by "the mass of ammonium carbonate is 0.6% of the mass of the precursor", and the amount of Li2CO3 is increased from 0.67 mol (0 0.65 mol excess 3at%) is reduced to 0.492 mol (0.477 mol excess 3at%), and compounds containing doping elements WO3, Nb2O5, Al2O3, NH4H2PO4, LiF, and Li2S are added to the first mixture, wherein the ratios of the atomic weights of W, Nb, Al, P, F, and S elements to the atomic weight of nickel in the precursor are 1:29.4, 1:29.4, 1:29.4, 1:29.4, 1:2.94, and 1:2.94, respectively, while other conditions remain unchanged, to obtain the positive electrode material Li 1.129 Ni 0.294 Mn 0.547 W 0.01 Nb 0.01 Al 0.01 P 0.01 O 1.8 F 0.1 S 0.1 .

[0141] Example 10

[0142] The preparation process is basically the same as that of Example 1, except that in step (1), "the concentration of sodium hypochlorite in the reaction system is 0.5 g / L" is replaced by "the concentration of sodium hypochlorite in the reaction system is 0.9 g / L", and other conditions remain unchanged to obtain a precursor; in step (2), the precursor of Example 1 is replaced by the precursor of this example; "ammonium sulfate" is replaced by "ammonium carbonate"; "the mass of ammonium sulfate is 0.6% of the mass of the precursor" is replaced by "the mass of ammonium carbonate is 0.7% of the mass of the precursor", and the amount of Li2CO3 is increased from 0.67 mol (0. The amount of the doping element was reduced from 65 mol (3 at% excess) to 0.492 mol (3 at% excess) and compounds containing doping elements such as WO3, Nb2O5, Al2O3, NH4H2PO4, LiF and Li2S were added to the first mixture, wherein the ratios of the atomic weights of the elements W, Nb, Al, P, F and S to the atomic weight of the element nickel in the precursor were 1:29.4, 1:29.4, 1:29.4, 1:29.4, 1:2.94 and 1:2.94, respectively, while other conditions remained unchanged, to obtain the first sintered product Li 1.129 Ni 0.294 Mn 0.547 W 0.01 Nb 0.01 Al 0.01 P 0.01 O 1.8 F 0.1 S 0.1 ;

[0143] Add step (3): mix the first sintering product with 0.03 mol% Al2O3 and 0.03 mol% AlPO4 to obtain a second mixture; perform a second sintering treatment on the second mixture at a sintering temperature of 550°C, in an air atmosphere, for 10 h to obtain a positive electrode material (0.03Al2O3·0.03AlPO4·Li 1.13 Ni 0.292 Mn 0.548 W 0.01 Nb 0.01 Al 0.01 P 0.01 O2).

[0144] Comparative Example 1

[0145] The preparation process is basically the same as that in Example 1, except that in step (1), "the concentration of sodium hypochlorite in the reaction system is 0.5 g / L" is replaced by "the concentration of sodium hypochlorite in the reaction system is 2.5 g / L", and other conditions remain unchanged to obtain a precursor; in step (2), the precursor of Example 1 is replaced by the precursor of this comparative example; "ammonium sulfate" is replaced by "ammonium bicarbonate"; "the mass of ammonium sulfate is 0.6% of the mass of the precursor" is replaced by "the mass of ammonium bicarbonate is 3.0% of the mass of the precursor", and other conditions remain unchanged to obtain a positive electrode material Li 1.13 Ni 0.304 Mn 0.566 O2.

[0146] Comparative Example 2

[0147] The preparation process is basically the same as that in Example 1, the difference is that in step (1), "the concentration of sodium hypochlorite in the reaction system is 0.5 g / L" is replaced by "the concentration of sodium hypochlorite in the reaction system is 2.2 g / L", and other conditions remain unchanged to obtain a precursor; in step (2), the precursor of Example 1 is replaced by the precursor of this comparative example; "the mass of ammonium sulfate is 0.6% of the mass of the precursor" is replaced by "the mass of ammonium bisulfate is 1.6% of the mass of the precursor", and other conditions remain unchanged to obtain a positive electrode material Li 1.131 Ni 0.304 Mn 0.565 O2.

[0148] Comparative Example 3

[0149] The preparation process is basically the same as that of Example 1, except that sodium hypochlorite is not added to the reaction system in step (1), and other conditions remain unchanged to obtain a precursor; in step (2), the precursor of Example 1 is replaced by the precursor of this comparative example; ammonium sulfate is not added, and other conditions remain unchanged to obtain the positive electrode material Li 1.129 Ni 0.307 Mn 0.563 O2.

[0150] Comparative Example 4

[0151] The preparation process is basically the same as that in Example 1, except that the "metal salt solution is a sulfate solution containing nickel and manganese (nickel-manganese molar ratio of 35:65)" in step (1) is replaced by "the metal salt solution is a sulfate solution containing nickel, cobalt and manganese (nickel, cobalt, manganese molar ratio of 30:10:60)"; "the sodium hypochlorite concentration in the reaction system is 0.5 g / L" is replaced by "the sodium hypochlorite concentration in the reaction system is 2.4 g / L", and other conditions remain unchanged to obtain a precursor; in step (2), the precursor of Example 1 is replaced by the precursor of this comparative example; "ammonium sulfate" is replaced by "ammonium carbonate"; "the mass of ammonium sulfate is 0.6% of the mass of the precursor" is replaced by "the mass of ammonium carbonate is 2.3% of the mass of the precursor", and other conditions remain unchanged to obtain the positive electrode material Li 1.130 Ni 0.26 Co 0.089 Mn 0.521 O2.

[0152] Comparative Example 5

[0153] The preparation process is basically the same as that in Example 1, except that the "metal salt solution is a sulfate solution containing nickel and manganese (nickel-manganese molar ratio is 35:65)" in step (1) is replaced by "the metal salt solution is a sulfate solution containing nickel, cobalt and manganese (nickel, cobalt, manganese molar ratio is 30:10:60)"; sodium hypochlorite is not added to the reaction system, and other conditions remain unchanged to obtain a precursor; in step (2), the precursor of Example 1 is replaced by the precursor of this comparative example; ammonium sulfate is not added, and other conditions remain unchanged to obtain the positive electrode material Li 1.129 Ni 0.261 Co 0.088 Mn 0.523 O2.

[0154] Test example

[0155] 1. Porosity determination

[0156] The positive electrode material was polished using a cross-section polisher and photographed under a scanning electron microscope. ImageJ software was then used to quantitatively analyze the grayscale of the positive electrode material cross section. Specifically, the RGB threshold was first set to 90, and the area ratio of the region in the RGB range of 0 to 90 in the positive electrode material image was obtained, recorded as X1. Similarly, the area ratio of the region in the RGB range of 0 to 252 in the positive electrode material image was recorded as X2, and the cross-sectional porosity of the positive electrode material was obtained as X1 / X2×100%.

[0157] The average porosity of the positive electrode material is obtained by taking the average value of the porosity measurements of more than 20 secondary particles in the sample.

[0158] 2. Particle size determination

[0159] Dmin In the volume-based particle size distribution, the particle size of the positive electrode material particles from the smallest particle size side to the point where the volume accumulation reaches 0% is D min ;D 50 In the volume-based particle size distribution, the particle size of the positive electrode material particles at the point where the cumulative volume reaches 50% is D. 50 .

[0160] 3. Energy density

[0161] The energy density recorded in Table 1 is the volume energy density of the positive electrode material itself coated on the positive electrode sheet, that is, the average discharge voltage × specific capacity × electrode sheet compaction density.

[0162] 4. Electrochemical performance test

[0163] The above-mentioned positive electrode material was mixed with the conductive agent Super-P and the binder PVDF in a mass ratio of 92:4:4, and an appropriate amount of NMP solution was added to form a slurry. The slurry was coated on aluminum foil and baked in a vacuum oven at 150°C for 12 hours after drying. After that, the secondary battery was assembled in an Ar gas atmosphere glove box. Metallic lithium was used as the negative electrode, and 1 mol / L LiPF6 dissolved in a mixed organic solvent with a volume ratio of EC:EMC=3:7 was used as the electrolyte to assemble into a button-type CR2032 battery.

[0164] (1) 0.1C specific capacity, discharge voltage: 0.1C = 23mAg -1 The battery is discharged at a current density of 4.55V from a full charge to a voltage of 2.5V. The corresponding capacity is the discharge specific capacity of 0.1C. The specific energy / specific capacity of 0.1C discharge is used to obtain the average discharge voltage of 0.1C discharge.

[0165] (2) 2.0C specific capacity: 2.0C = 460mAg -1 The battery is discharged at a current density of 1000 volts from a full charge of 4.55 V to a voltage of 2.5 V. The corresponding capacity is the 2.0C discharge specific capacity. (3) 2C / 0.1C capacity retention rate: The value obtained by dividing the 2.0C discharge specific capacity in (2) by the 0.1C discharge specific capacity in (1) is the 2C / 0.1C capacity retention rate.

[0166] (4) 200-cycle energy retention rate: 200 cycles are performed at 0.5C / 1.0C. The percentage of the discharge specific energy at the 200th cycle / the discharge specific energy at the first cycle is the 200-cycle energy retention rate.

[0167] (5) Average porosity growth rate of the cycle profile (%): 200 cycles were performed at a charge and discharge rate of 0.5C / 1.0C. The average porosity of the material profile before the cycle was recorded as P, and the average porosity of the material profile after the cycle was recorded as Q. Then (QP) / P×100% is the average porosity growth rate of the cycle profile.

[0168] Refer to Figures 1 to 21 for the SEM test, and see Table 1 for the test results.

[0169] Table 1

[0170] According to Table 1, the embodiments all satisfy δ=β-[2α+75γ] / 3, and 0≤δ≤4.0. The 2C / 0.1C capacity retention rate of the embodiment is above 84%, and the 200-week energy retention rate is above 94%, both of which are higher than the comparative example. The average porosity growth rate of the positive electrode material of the embodiment after 200 cycles is less than 2%, which is much lower than that of the comparative example. In addition, the compaction density, specific capacity, discharge voltage, and energy density of the positive electrode sheet in the embodiment are comparable to those of the comparative example, or even higher than those of the embodiment. It can be seen that the positive electrode material provided in this application can maximize the specific capacity, rate performance, cycle performance, and long cycle life of the lithium-ion battery prepared from the positive electrode material by matching the average particle size, lithium richness, and average porosity, and can especially improve the electrochemical performance under high voltage conditions.

[0171] The above describes in detail the preferred embodiments and experimental verifications of the present application. It should be understood that ordinary skill in the art can make numerous modifications and variations based on the concepts of the present application without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art based on the concepts of the present application through logical analysis, reasoning, or limited experimentation on the basis of the existing technology should be within the scope of protection defined by the claims.

Claims

1. A positive electrode material, wherein: The Dv50 value of the positive electrode material is α, in μm; The lithium-rich content of the positive electrode material is γ; The average porosity of the positive electrode material is expressed as β%, Among them, α, β, and γ satisfy: δ=β-[2α+75γ] / 3, where 0≤δ≤4.

0.

2. The positive electrode material according to claim 1, wherein The positive electrode material includes secondary particles and a coating layer covering at least a portion of the surface of the secondary particles.

3. The positive electrode material according to claim 2, wherein The total molar amount of elements distributed in the secondary particles in the form of cations is A, and the total molar amount of elements distributed in the secondary particles in the form of anions is B, and A and B satisfy: 0.985≤A / B≤1.

0.

4. The positive electrode material according to claim 3, wherein The secondary particles contain doped metal elements distributed in the form of cations and doped non-metal elements distributed in the form of anions; Wherein, the molar ratio of the doped metal element to the elements other than lithium ions distributed in the secondary particles in the form of cations is not higher than 5%; and / or, The molar ratio of the doped non-metallic element to the total amount of elements distributed in the secondary particles in the form of anions is not higher than 10%.

5. The positive electrode material according to any one of claims 2 to 4, wherein The chemical formula of the secondary particles is Li 1+x-2y M z M' 1-x-z O 2-y-t R t , where M is Ni a Co b Mn c , a+b+c=1.0, 0≤b≤0.10, a≥2b, 1.5≤c / (a+b)≤3.0, x=(ca) / (2+ca), 0.985≤(2-2y) / (2-y)≤1.0, (19-19x) / 20≤z≤(1-x), 0≤t≤(2-y) / 10; Wherein, M' is a doped metal element, and R is a doped non-metal element.

6. The positive electrode material according to claim 5, wherein The M' comprises at least one of Cr, Mo, W, Ta, Nb, P, Sb, Te, Hf, Ce, Ti, Zr, Sn, La, Al, Mg, Fe, K, and Na; and / or, The R includes at least one of F and S.

7. The positive electrode material according to any one of claims 2 to 6, wherein: The Dv50 of the positive electrode material is 2.5 to 10.6 μm; and / or, The minimum particle size Dv of the positive electrode material min not less than 0.6 μm; and / or, The secondary particles are formed by agglomeration of primary particles, and the average thickness of the primary particles is 80 to 250 nm; and / or, The specific surface area of ​​the secondary particles is not less than 0.5 m 2 / g, and not higher than 1.5m 2 / g; and / or, β is 7 to 13; and / or, The lithium-rich amount γ is 0.09 to 0.

21.

8. The positive electrode material according to any one of claims 2 to 7, wherein: The molar ratio of the coating layer material to the total molar ratio of the positive electrode material is (0.2-1.0):100; and / or, The coating layer material is phosphate and / or inert oxide; the phosphate includes at least one of AlPO4 and LaPO4, and the inert oxide includes at least one of Al2O3, TiO2, ZrO2, and La2O3.

9. A method for preparing the positive electrode material according to any one of claims 1 to 8, wherein: The following steps are involved: A metal salt solution, an alkaline solution and an oxidant are mixed to obtain a reaction system, and a precipitation reaction is performed in the reaction system to obtain a precursor; wherein the oxidant comprises sodium hypochlorite, and the concentration of the oxidant in the reaction system is 0.2 to 2 g / L; The precursor, the lithium salt and the pore-forming agent are mixed to obtain a first mixed material, and the first mixed material is subjected to a first sintering treatment to obtain a positive electrode material.

10. The preparation method according to claim 9, wherein: The first mixture also includes a compound containing a doping element; and / or, After the first sintering process, the method further comprises: mixing the first sintering product with a coating layer material to obtain a second mixture; The second mixture is subjected to a second sintering process to obtain a positive electrode material.

11. The preparation method according to claim 10, wherein: The conditions of the precipitation reaction are: stirring speed 700-800 rpm, temperature 50-70° C., pH 9.5-11.5; The temperature of the first sintering treatment is 800-950° C., and the holding time is 10-15 hours; and / or, The coating layer material includes an inert oxide, the second sintering treatment is performed at a temperature of 500 to 800° C., a heating rate of 5 to 10° C. / min, and a time of 5 to 10 hours; and / or, The coating layer material includes phosphate, the temperature of the second sintering treatment is 700-900° C., the heating rate is 5-10° C. / min, and the time is 5-10 hours.

12. The preparation method according to any one of claims 9 to 10, wherein: The mass of the pore former is 0.1-1.0wt% of the mass of the precursor; The pore-forming agent includes at least one of ammonium carbonate, ammonium sulfate, ammonium persulfate, ammonium nitrate and ammonium chloride.

13. A positive electrode sheet, wherein: The positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 8 or the positive electrode material prepared by the preparation method according to any one of claims 9 to 12.

14. The positive electrode sheet according to claim 13, wherein: The positive electrode sheet comprises a current collector and a positive electrode active material layer located on at least one functional surface of the current collector; The positive electrode active material layer comprises the positive electrode material according to any one of claims 1 to 8, a conductive agent, and a binder, wherein the mass of the positive electrode material accounts for no less than 94 wt % of the total mass of the positive electrode active material layer.

15. A lithium ion battery, wherein: The lithium-ion battery comprises the positive electrode sheet according to claim 13.

16. The lithium ion battery according to claim 15, wherein: The lithium-ion battery also includes a separator, a negative electrode sheet and an electrolyte; The negative electrode sheet is selected from at least one of a lithium sheet, graphite, and a silicon-carbon negative electrode.

17. The lithium ion battery according to claim 15 or 16, wherein: After the lithium-ion battery is cycled for 200 cycles under the charge and discharge conditions of 2.5-4.55V and 0.5C / 1.0C, the growth rate of the cross-section average porosity of the positive electrode material on the positive electrode sheet is less than 2%.

18. An electrical device, wherein: Comprising the lithium-ion battery according to any one of claims 15 to 17, preferably, the electrical equipment comprises an electric car, a manned electric aircraft, or a drone.

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