Positive electrode lithium supplement agent and preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion battery positive electrode materials, and particularly discloses a positive electrode lithium supplement agent and a preparation method and application thereof. The positive electrode lithium supplementing agent is of a core-shell structure, an inner core is doped lithium-rich lithium cobalt oxide, an outer shell is spinel lithium cobalt oxide, and the doped lithium-rich lithium cobalt oxide is specifically Li6CoO4 doped with Al, Mg and Zr; the preparation method comprises the following steps: preparing and uniformly mixing an aluminum source, a magnesium source, a zirconium source, a lithium source and a cobalt source according to a specific stoichiometric ratio, and then carrying out high-temperature solid-phase sintering and crushing in an inert atmosphere; preparing and uniformly mixing the one-step product, a cobalt source and a lithium source according to a specific stoichiometric ratio, and then carrying out low-temperature solid-phase sintering in an inert atmosphere; and crushing and sieving. The preparation method of the positive electrode lithium supplementing agent is suitable for large-scale and industrial production, and after the positive electrode lithium supplementing agent is applied to a high-voltage lithium cobalt oxide positive electrode and forms a battery cell with a silicon-based negative electrode, the battery cell has smaller gas production rate and better cycling stability, and the first-week irreversible capacity loss of the silicon-based negative electrode is effectively compensated.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode materials for lithium-ion batteries, and specifically discloses a cathode lithium supplement agent, a preparation method thereof and an application thereof. The cathode lithium supplement agent is particularly suitable for high-voltage lithium cobaltate cathode materials. Background Art

[0002] The combination of a high-voltage lithium cobaltate cathode and a silicon-based anode can achieve the design of high-energy density consumer battery cells. However, the silicon-based anode has a large irreversible capacity loss during the first cycle and cycling process, resulting in a loss of the energy density and cycling performance of the battery cells. Compared with the lithium supplement technology on the anode side, the lithium supplement on the cathode side has higher operability. By adding a cathode lithium supplement agent to the cathode slurry, part of the irreversible capacity loss in the first cycle of the anode can be compensated. Lithium-rich cobaltate (Li6CoO4) has been practically applied as a cathode lithium supplement agent in lithium-ion batteries. It can effectively compensate for the irreversible capacity loss in the first cycle of the battery, but at the same time, it also brings adverse effects, including optimization of the homogenization process, increase in the surface resistance of the electrode, gas generation in the battery cell, acceleration of side reactions caused by the catalysis of transition metals on the electrolyte after lithium deintercalation, and acceleration of the cycling decay of the battery cell, etc.

[0003] Based on the application status of the Li6CoO4 lithium supplement agent, the prior art has tried to improve it through means such as surface modification, doping modification, nanosizing, composite material development, electrolyte optimization, prelithiation technology, etc. These methods have improved the electrochemical performance and stability of the Li6CoO4 lithium supplement agent to a certain extent. However, when applied to high-voltage lithium cobaltate cathode materials and matched with silicon-based anodes, the compensation effect for the first irreversible capacity loss is limited, and challenges such as structural stability, electrolyte decomposition and interfacial side reactions lead to unsatisfactory cycling performance.

[0004] How to develop a cathode lithium supplement agent with a higher compatibility with the high-voltage lithium cobaltate cathode / silicon-based anode system is of great significance. For this reason, this application is proposed. Summary of the Invention

[0005] In view of the above-mentioned disadvantages of the prior art, the present invention provides a cathode lithium supplement agent, a preparation method thereof and an application thereof.

[0006] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0007] First, the present invention proposes a cathode lithium supplement agent with a core-shell structure. The inner core is doped lithium-rich cobaltate, and the outer shell is spinel lithium cobaltate. The doped lithium-rich cobaltate is specifically Li6CoO4 doped with Al, Mg, and Zr.

[0008] The stability of Li6CoO4 is poor, which greatly affects its electrochemical performance and application. The doping of Al, Mg, and Zr in it has the following effects: The doping of Al can enhance the structural stability and thermal stability: Al3+ Substituted Co 3+ can stabilize the crystal structure, inhibit phase transformation, improve cycle stability, enhance the thermal stability of the material, and reduce the risk of thermal runaway; the doping of Mg can stabilize the structure and improve electronic conductivity: Mg 2+ has an ionic radius similar to that of Li + and can partially replace Li + to enhance the structural stability of the material and reduce volume changes during cycling; the doping of Mg can also improve the electronic conductivity of the material and then enhance the rate performance; the doping of Zr can stabilize the structure and improve ionic conductivity: Zr 4+ doping can not only enhance the crystal structure stability, reduce structural degradation during cycling, but also expand the lithium-ion diffusion channels, improve ionic conductivity, and enhance the rate performance. Therefore, the synergistic effect of Mg and Zr can simultaneously improve the electronic conductivity and ionic conductivity of the material and enhance the rate performance; the synergistic effect of Al and Zr helps to improve the thermal stability of the material and reduce the risk of thermal runaway; the co-doping and synergistic effect of Mg, Al, and Zr can effectively improve the comprehensive performance of the material.

[0009] Based on the doping of Al, Mg, and Zr in Li6CoO4, a spinel lithium cobaltate shell is coated on its outer layer. This shell can effectively isolate the moisture in the electrolyte and the environment, improve the stability of Li6CoO4, form a supporting structure, enhance the surface structure stability of the lithium supplement agent, and avoid material failure caused by contact with air during the use of the lithium supplement agent; at the same time, it can effectively inhibit the side reactions caused by the delithiation of the lithium supplement agent, and can also effectively improve the compatibility of the lithium supplement agent with the high-voltage electrolyte, and form a CEI on the surface of the lithium supplement agent particles.

[0010] The doped lithium-rich cobaltate core and the spinel lithium cobaltate shell act synergistically and influence each other, effectively compensating for the irreversible capacity loss in the first cycle of the silicon-based anode, thereby enhancing the energy density and cycle performance of the battery cell.

[0011] Furthermore, due to Al 3+Do not participate in the electrochemical reaction. The doping of excessive Al may lead to a decrease in the material capacity. The doping of excessive Mg may cause the diffusion channels of lithium ions to be blocked, thereby reducing the lithium ion conductivity. While the doping of excessive Zr may lead to a decrease in the material capacity and increase the usage cost. Therefore, there are both minimum addition amounts considered to ensure a significant improvement in performance after doping and maximum addition amount limits to avoid negative impacts for the doping amounts of Al, Mg, and Zr. If the mass percentages of Co, Al, Mg, and Zr in the doped lithium-rich cobaltate are represented by n, x, y, and z respectively, then n, x, y, and z satisfy: 34.5% < n < 36%, 0.01% ≤ x ≤ 0.6%, 0.01% ≤ y ≤ 0.3%, 0.01% ≤ z ≤ 0.3%. Considering the synergistic effect of the three doping elements and to maintain the stability of the main structure, and to balance performance optimization and capacity loss, the sum of the mass percentages of the three doping elements satisfies: x + y + z ≤ 1.2%. Within this range, the doping amounts of the three doping elements are reasonable, which can not only improve the lithium supplement performance of Li6CoO4 but also avoid negative impacts, ensuring its high efficiency and stability in the application of high-voltage lithium cobaltate cathode materials;

[0012] Furthermore, the core-doped lithium-rich cobaltate satisfies: D50 = 3 - 10 μm, (D90 - D10) / D50 = 0.5 - 2.5, and BET is 0.1 - 1 m 2 / g; Preferably, the core-doped lithium-rich cobaltate satisfies: D50 is 4 - 7 μm, (D90 - D10) / D50 = 1.0 - 1.5, and BET is 0.2 - 0.6 m 2 / g.

[0013] Since the true density of this cathode lithium supplement agent is lower than that of the high-voltage lithium cobaltate cathode material, the small particle size design of the cathode lithium supplement agent is similar to the small particle size in lithium cobaltate, which can fill the gaps between the particles of the high-voltage lithium cobaltate cathode material, thereby effectively reducing the pole piece compaction loss caused by the low density of the lithium supplement agent. In the present invention, the particle size range of the cathode lithium supplement agent constructed by the core meeting the above requirements is moderate, which not only helps to reduce the pole piece compaction loss but also can optimize the lithium ion diffusion path, improve the lithium supplement uniformity, and enhance the mechanical strength.

[0014] (D90 - D10) / D50 is called the particle size distribution width coefficient or the dispersion coefficient, which can be used to measure the width of the particle size distribution. The dispersion coefficient should not be too small. If it is too small, it indicates that the distribution is too narrow. If the particle size distribution is too narrow, that is, the particles are almost the same size, the voids between the particles are large, and it is difficult to pack tightly, resulting in a decrease in the compaction density of the electrode sheet, which is not conducive to improving the energy density of the electrode sheet. Moreover, an overly narrow particle size distribution will also lead to poor fluidity and difficulty in uniform dispersion during the preparation of the electrode sheet, resulting in uneven electrode sheet thickness or local accumulation, etc.; the dispersion coefficient should not be too large. If it is too large, it indicates that the distribution is too wide, that is, the particle sizes vary greatly, which will not only increase the porosity of the electrode sheet and reduce the compaction density, but also cause particle stratification during the preparation and coating of the slurry, resulting in poor uniformity of the electrode sheet, uneven electrochemical performance, and reduced mechanical strength. In the present invention, in order to achieve a high compaction density, uniformity, and good electrochemical performance of the electrode sheet, the ideal dispersion coefficient is controlled within 0.5 - 2.5, and preferably = 1.0 - 1.5.

[0015] When D50 and the dispersion coefficient (D90 - D10) / D50 simultaneously meet the above requirements, the obtained cathode lithium supplement agent is used in the high-voltage lithium cobaltate cathode active material to prepare a cathode slurry, which helps to obtain a cathode sheet with good uniformity, high compaction density, and excellent electrochemical performance.

[0016] Furthermore, the molecular formula of the spinel lithium cobaltate is Li m Co n O k , where: 0.8 ≤ m ≤ 1.2, n is 1 or 2, and k is 2 or 4;

[0017] Preferably, the molecular formula of the spinel lithium cobaltate is LiCo2O4 or low-temperature phase LiCoO2. LiCo2O4 has high electronic conductivity, can improve the surface conductivity of Li6CoO4, enhance the rate performance, and it can also form a stable interface with Li6CoO4 to reduce the interface impedance and improve the cycle performance; the low-temperature phase LiCoO2 has good structural stability and high ionic conductivity. After coating on the outer surface of the doped lithium-rich cobaltate, it will neither affect the diffusion of lithium ions nor can effectively protect the Li6CoO4 core;

[0018] Furthermore, the doped lithium-rich cobaltate has a tetragonal anti-fluorite structure, belonging to the P42 / nmc space group, and the unit cell parameters a and c respectively satisfy: The spinel lithium cobaltate belongs to the Fd3m space group;

[0019] Preferably, the unit cell parameter a of the doped lithium-rich cobaltate is c is 4.

[0021] Preferably, the coating amount of the shell is 0.1wt%-3wt% of the core;

[0022] Under the above coating amount, the shell will form a shell of moderate thickness on the surface of the doped lithium-rich lithium cobalt oxide with a limited particle size or BET. The shell should not be too thin or too thick. If it is too thin, it will not only fail to fully cover the outer surface of the core, resulting in the electrolyte still in contact with the core, but also easily break during the cycle and lose its protective effect. If it is too thick, it will not only hinder the diffusion of lithium ions, reduce the rate performance, but also reduce the proportion of active materials, resulting in a decrease in overall capacity. The shell formed by the above coating amount has a moderate thickness, which can effectively isolate the contact between the electrolyte and Li6CoO4, avoid the problem of transition metal dissolution, reduce side reactions, and will not significantly hinder the diffusion of lithium ions.

[0023] Secondly, the present invention provides a method for preparing the above-mentioned positive electrode lithium supplement, comprising the following steps:

[0024] S1, preparing aluminum source, magnesium source, zirconium source, lithium source and cobalt source according to a specific stoichiometric ratio and mixing them evenly, and then solid-phase sintering and crushing them at high temperature in an inert atmosphere to obtain a primary crushed material, i.e., Li6CoO4 doped with Al, Mg and Zr;

[0025] S2, mixing the primary crushed material with the cobalt source and the lithium source in a specific stoichiometric ratio, and then sintering them at low temperature in an inert atmosphere, so as to generate a layer of spinel lithium cobalt oxide in situ on the outer surface of the primary crushed material by low temperature solid phase sintering, so as to stabilize the surface and interface of the primary crushed material and reduce the residual alkali in the material;

[0026] S3. The product of the previous step is crushed and sieved to obtain a positive electrode lithium supplement agent with a designed gradation.

[0027] It should be noted that;

[0028] (1) The "uniform mixing" in step S1 and step S2 is mainly achieved by high-speed mixing equipment, which includes but is not limited to one or more of a high-speed ball mill mixer, a high-speed mixer, a VC mixer, and a plowshare mixer.

[0029] (2) The inert atmosphere in step S1 and step S2 includes, but is not limited to, one or more of nitrogen, argon, and helium.

[0030] (3) In step S1 and step S2, the sintering furnace is used to reach the target sintering temperature by programmed heating, and the heating rate is preferably 1-10°C / min.

[0031] (4) In step S1 and step S2, no matter whether the sintering is performed at high temperature or low temperature, the inert gas is continuously introduced after the sintering is completed until the material reaches room temperature.

[0032] Furthermore, in step S1, the temperature of the high-temperature solid-phase sintering is 500 - 1000 °C, the time is 4 - 20 h, and the actually added amount of the lithium source is 0.1% - 5% in excess of its theoretically added amount; in step S2, the temperature of the low-temperature solid-phase sintering is 300 - 800 °C, the time is 4 - 16 h, and the actually added amount of the lithium source is 0.1% - 4% in excess of its theoretically added amount.

[0033] Preferably, in step S1, the temperature of the high-temperature solid-phase sintering is 700 - 800 °C, the time is 8 - 16 h, and the actually added amount of the lithium source is 1% - 3% in excess of its theoretically added amount.

[0034] Preferably, in step S2, the temperature of the low-temperature solid-phase sintering is 400 - 600 °C, the time is 8 - 16 h, and the actually added amount of the lithium source is 1% - 2.5% in excess of its theoretically added amount.

[0035] Preferably, the particle size D50 of the cobalt source in both step S1 and step S2 is 2 - 9 μm. The cobalt source in S1 is aluminum-doped cobalt tetroxide, and the cobalt source in S2 is selected from one or more of cobalt tetroxide, cobaltous oxide, cobalt hydroxide, cobalt oxyhydroxide, and cobalt carbonate.

[0036] Preferably, the lithium sources in step S1 and step S2 are the same or different, and are each selected from one or more of lithium oxide, lithium peroxide, lithium hydroxide, and lithium carbonate.

[0037] Preferably, the particle size of the magnesium source in step S1 is not greater than 200 nm, and it is selected from one or more of magnesium oxide, magnesium hydroxide, magnesium carbonate, basic magnesium carbonate, and magnesium oxalate.

[0038] Preferably, the particle size of the zirconium source in step S1 is not greater than 200 nm, and it is selected from one or more of zirconium dioxide, zirconium hydroxide, zirconium carbonate, basic zirconium carbonate, and zirconium oxalate.

[0039] Thirdly, the present invention provides a positive electrode sheet, and the active material thereon includes a positive electrode active material and the above-mentioned positive electrode lithium supplementing agent. The positive electrode active material includes at least one of lithium cobaltate, lithium manganate, lithium nickel cobalt manganate, lithium iron phosphate, and lithium manganese iron phosphate.

[0040] Furthermore, the positive electrode active material is high-voltage lithium cobaltate, and the addition amount of the positive electrode lithium supplementing agent in the positive electrode slurry is 0.1% - 10%, preferably 0.5% - 3%, such as 1% or 2%. In specific practice, it can be flexibly adjusted or selected according to specific circumstances, and the present invention does not make any restrictions.

[0041] Fourthly, the present invention provides a lithium battery, which includes a silicon-based negative electrode sheet and the above-mentioned positive electrode sheet. The silicon content in the silicon-based negative electrode sheet is 0.1-100%, and the charging cut-off voltage of the lithium battery is ≥4.5V.

[0042] Compared with the prior art, the present invention has at least the following beneficial effects:

[0043] 1. The positive electrode lithium supplement agent of the present invention is designed as a core-shell structure. The inner core is Li6CoO4 doped with Al, Mg, and Zr, and the outer shell is spinel lithium cobaltate. The inner core and the outer shell act synergistically and influence each other. After being applied to the high-voltage lithium cobaltate positive electrode and forming an electric core with the silicon-based negative electrode, it has a smaller gas generation amount and better cycle stability, effectively compensating for the irreversible capacity loss of the silicon-based negative electrode in the first cycle.

[0044] 2. In the preparation method of the positive electrode lithium supplement agent proposed by the present invention, the raw materials and the process implementation path are basically similar to the industrial production method of the lithium cobaltate positive electrode material. Therefore, the production line of the lithium cobaltate positive electrode material can be adopted, which is suitable for large-scale and industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0046] Figure 1 XRD pattern of Example 1;

[0047] Figure 2 High-temperature cycle performance curves of the soft-pack batteries obtained in Example 1, Comparative Example 3, and Comparative Example 5 at 45°C. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts belong to the scope of protection of the present application.

[0049] It should be noted that: the following technical solutions not described in detail all adopt the conventional technical means in the art. All kinds of raw materials involved in the following examples and comparative examples are commercially available.

[0050] Example 1

[0051] A positive electrode lithium supplement agent is prepared according to the following operation steps:

[0052] S1. The aluminum source, magnesium source, zirconium source, lithium source, and cobalt source are proportioned according to the doping mass percentages of Al, Mg, and Zr being 0.4%, 0.1%, and 0.05% in sequence and mixed evenly via a high-speed mixer. The actual added amount of substance of the lithium source is 2% in excess of its theoretical added amount. Then, it is sintered at 750 °C for 16 h and pulverized in an inert atmosphere to obtain a first pulverized material, that is, a core-doped lithium-rich cobaltate is obtained. Among them, cobalt aluminate doped with aluminum with a D50 of 2 - 9 μm is used as both the aluminum source and the cobalt source, the magnesium source and the zirconium source are respectively from magnesium oxide and zirconia with particle sizes not greater than 200 nm, and the lithium source is lithium oxide. After testing, the obtained doped lithium-rich cobaltate has a tetragonal anti-fluorite structure, belongs to the P42 / nmc space group, and the lattice parameter a is c is

[0053] S2. The first pulverized material, cobalt source, and lithium source are proportioned according to coating the spinel phase LiCo2O4 with a coating amount of 0.5% and mixed evenly via a high-speed mixer. The actual added amount of substance of the lithium source is 1.5% in excess of its theoretical added amount. Then, it is sintered at 500 °C for 16 h in an inert atmosphere. Among them, the cobalt source is cobalt tetroxide with a particle size D50 of 4 - 6 μm, and the lithium source is lithium oxide;

[0054] S3. After the product of the previous step is cooled to room temperature, it is pulverized and sieved, and the product meeting the following requirements is selected: D50 = 3 - 10 μm, (D90 - D10) / D50 = 0.5 - 2.5, BET is 0.1 - 1 m 2 / g.

[0055] The obtained cathode lithium supplement agent is mixed with 4.55V high-voltage cobaltate, conductive carbon nanotubes, conductive carbon black, and PVDF binder at mass percentages of 1%, 97%, 0.5%, 0.5%, and 1% and made into a cathode electrode sheet via homogenization and coating. The silicon-carbon anode, conductive carbon nanotubes, conductive carbon black, CMC, and SBR are mixed at mass percentages of 94%, 1%, 0.5%, 0.5%, and 1% and made into an anode electrode sheet via homogenization and coating, where: the silicon content in the silicon-carbon anode is 5%. A PE-based membrane coated with alumina ceramic is used as the separator, and 1MLiPF6 - 3%FEC - PP / EC / DEC (volume ratio 3:2:5) - 3% HTCN is used as the electrolyte, and a soft-pack full cell is formed with the above-mentioned cathode electrode sheet and anode electrode sheet for electrochemical testing. During electrochemical testing, the first charge-discharge gram capacity is obtained by 0.2C formation and grading. The obtained soft-pack full cell is subjected to a high-temperature cycle at 45 °C to detect its long-term cycle stability, and the cycle operation is as follows: step charging at 3.5C to 4.55V and then constant-voltage charging to 0.05C cut-off, and then discharging at 0.7C to 3.0V.

[0056] Example 2

[0057] Compared with Example 1, the coating amount in step S2 is adjusted from 0.5% to 0.1%, and the rest is the same as that of Example 1.

[0058] Example 3

[0059] Compared with Example 1, the coating amount in step S2 is adjusted from 0.5% to 1%, and the rest is the same as that of Example 1.

[0060] Example 4

[0061] Compared with Example 1, the coating amount in step S2 is adjusted from 0.5% to 2%, and the rest is the same as that of Example 1.

[0062] Example 5

[0063] Compared with Example 1, the coating amount in step S2 is adjusted from 0.5% to 3%, and the rest is the same as that of Example 1.

[0064] Example 6

[0065] Compared with Example 1, the silicon-carbon negative electrode used in preparing the negative electrode plate is a silicon-carbon negative electrode with a silicon content of 10%, and the rest is the same as that of Example 1.

[0066] Example 7

[0067] Compared with Example 1, the silicon-carbon negative electrode used in preparing the negative electrode plate is a silicon-carbon negative electrode with a silicon content of 20%, and the rest is the same as that of Example 1.

[0068] Example 8

[0069] Compared with Example 1, the silicon-carbon negative electrode used in preparing the negative electrode plate is a silicon-carbon negative electrode with a silicon content of 30%, and the rest is the same as that of Example 1.

[0070] Example 9

[0071] Compared with Example 1, the addition amount of the positive electrode lithium supplement in the positive electrode slurry is adjusted from 1% to 2%, that is, the positive electrode slurry includes the following components by mass percentage: 2% of positive electrode lithium supplement, 96% of 4.55V high-voltage cobaltate, 0.5% of carbon nanotubes, 0.5% of conductive carbon black, and 1% of PVDF binder, and the rest is the same as that of Example 1.

[0072] Example 10

[0073] Compared with Example 1, the coated spinel phase in step S2 is adjusted from LiCo2O4 to LiCoO2, and the rest is the same as that of Example 1.

[0074] Example 11

[0075] Compared with Example 1, in step S2, the coated spinel phase is adjusted from LiCo2O4 to Li 0.8 Co2O4, and the rest are the same as in Example 1.

[0076] Example 12

[0077] Compared with Example 1, in step S2, the coated spinel phase is adjusted from LiCo2O4 to Li 1.2 CoO2, and the rest are the same as in Example 1.

[0078] Example 13

[0079] Compared with Example 1, in step S2, the coating amount is adjusted from 0.5% to 0.3%, and the rest are the same as in Example 1.

[0080] Example 14

[0081] Compared with Example 1, in step S2, the coating amount is adjusted from 0.5% to 0.7%, and the rest are the same as in Example 1.

[0082] Comparative Example 1

[0083] A positive electrode sheet is prepared by mixing lithium cobaltate at a high voltage of 4.55V, carbon nanotubes, carbon black, and PVDF binder in a mass percentage of 97%, 1%, 1%, and 1%, and then homogenizing and coating. The negative electrode sheet, separator, and electrolyte are the same as in Example 1, and a soft-pack full cell is assembled for electrochemical testing. The electrochemical testing operation is the same as in Example 1.

[0084] Comparative Example 2

[0085] The positive electrode lithium supplement agent in Example 1 is adjusted to Li6CoO4 without any doping and coating, and the rest are the same as in Example 1.

[0086] Comparative Example 3

[0087] Compared with Example 1, in the preparation of the positive electrode lithium supplement agent, step S2 is not performed, that is, only doped lithium-rich cobaltate is obtained by doping without coating, and the rest are the same as in Example 1.

[0088] Comparative Example 4

[0089] Compared with Example 1, in step S1 of the preparation of the positive electrode lithium supplement agent, only Al is doped, and Mg and Zr are not doped, and the rest are the same as in Example 1.

[0090] Comparative Example 5

[0091] Compared with Example 1, in step S1 of the preparation of the positive electrode lithium supplement agent, Al, Mg, and Zr are not doped, and the rest are the same as in Example 1.

[0092] Comparative Example 6

[0093] Compared with Example 1, when preparing the cathode lithium supplement agent, only Mg is doped in step S1, and Al and Zr are not doped, and the rest are the same as in Example 1.

[0094] Comparative Example 7

[0095] Compared with Example 1, when preparing the cathode lithium supplement agent, only Zr is doped in step S1, and Al and Mg are not doped, and the rest are the same as in Example 1.

[0096] Comparative Example 8

[0097] Compared with Example 1, when preparing the cathode lithium supplement agent, only Al and Mg are doped in step S1, and Zr is not doped, and the rest are the same as in Example 1.

[0098] Comparative Example 9

[0099] Compared with Example 1, when preparing the cathode lithium supplement agent, only Al and Zr are doped in step S1, and Mg is not doped, and the rest are the same as in Example 1.

[0100] Comparative Example 10

[0101] Compared with Example 1, when preparing the cathode lithium supplement agent, only Mg and Zr are doped in step S1, and Al is not doped, and the rest are the same as in Example 1.

[0102] The key technical parameters of the above examples and comparative examples and the electrochemical test results of the assembled soft-pack full battery are shown in Table 1.

[0103] The larger the coating amount, the worse the lithium-ion and electron conduction performance, and the smaller the specific capacity; for the cycle data, when the coating amount is small, it is uneven, and when the coating is large, it hinders the lithium-ion and electron conduction.

[0104] Table 1

[0105]

[0106]

[0107] As Figure 1 、 Figure 2 and Table 1 together show that:

[0108] From Figure 1 it can be seen that the XRD pattern of the obtained cathode lithium supplement agent is consistent with the standard card PDF 78#1519 of Li6CoO4, belonging to the tetragonal anti-fluorite structure and the P42 / nmc space group. The XRD patterns of the remaining examples are close to Figure 1 each other, so they are not attached separately.

[0109] From the comparison of the test results of Examples 1 - 12, Comparative Example 1, and Comparative Example 2, it can be seen that: From the comparison of the test results of Comparative Example 1 and Comparative Example 2, it can be seen that adding the traditional lithium supplement Li6CoO4 to the 4.55V high-voltage lithium cobaltate cathode material can increase the specific capacity of the soft-pack battery, but at the same time, it will also deteriorate its high-temperature cycling performance. From the comparison of the test results of Examples 1 - 12 and Comparative Example 1, it can be seen that by using the cathode lithium supplement proposed in the present invention and adding it to the high-voltage lithium cobaltate cathode material, it can not only effectively compensate for the irreversible capacity of the silicon-based anode in the first cycle and increase the specific capacity of the battery, but also improve the cycling stability, and the 45°C high-temperature cycling performance of the obtained soft-pack battery is significantly improved. For example, in Examples 6, 7, and 8, the cathode lithium supplement proposed in the present invention, even when applied to a silicon-based anode with a relatively high silicon content, also has relatively good cycling performance.

[0110] Furthermore, from the comparison of the test results of Comparative Example 3, Comparative Example 5, and Example 1, it can be seen that: If only the core is doped without coating or only the core is coated without doping, there is a small improvement effect on the specific capacity of the battery, but it will still deteriorate the cycling performance of the battery (as Figure 2 shown), only by doping the core and coating the surface simultaneously to form a spinel lithium cobaltate shell can the irreversible capacity loss of the silicon-based anode in the first cycle be effectively compensated and the cycling performance of the battery be improved.

[0111] Regarding the core doping aspect, from the comparison of the test results of Comparative Example 4, Comparative Example 6 - Comparative Example 10, and Example 1, it can be seen that the core-doped lithium-rich cobaltate of the present invention must be doped with Al, Mg, and Zr simultaneously to obtain a cathode lithium supplement with good performance. For the three doping elements, adding one or two of them can, to a certain extent, increase the specific capacity of the battery and improve the cycling performance, but the improvement degree is limited. When the three doping elements are added simultaneously according to the addition amounts defined in the present invention, the high-temperature cycling performance of the battery is significantly improved, and the synergistic effect of Mg, Al, and Zr is self-evident. Regarding the selection of the chemical formula of the spinel phase in the coating layer, from the comparison of the test results of Example 1, Example 10, Example 11, and Example 12, it can be seen that the chemical formula of the spinel phase in the coating layer is preferably LiCo2O4 or LiCoO2.

[0112] In summary: In the present invention, the cathode lithium supplement agent is designed as a core-shell structure, with the inner core being Li6CoO4 doped with Al, Mg, and Zr, and the outer shell being spinel lithium cobalt oxide. The inner core and the outer shell act synergistically and influence each other. After being applied to the high-voltage lithium cobalt oxide cathode and forming an electric cell with a silicon-based anode, it has a smaller gas generation amount and better cycle stability, effectively compensating for the irreversible capacity loss in the first cycle of the silicon-based anode and improving the cycle performance. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and deformations to the above embodiments within the scope of the present invention. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

Claims

1. A cathode lithium supplement, characterized in that, It is a core-shell structure, the core is doped lithium-rich lithium cobalt oxide, and the shell is spinel lithium cobalt oxide. The doped lithium-rich lithium cobalt oxide is specifically Li6CoO4 doped with Al, Mg, and Zr.

2. The cathode lithium supplement according to claim 1, wherein In the doped lithium-rich cobaltate, the mass percentages of Co, Al, Mg, and Zr are represented by n, x, y, and z respectively, and n, x, y, and z satisfy: 34.5% < n < 36%, 0.01% ≤ x ≤ 0.6%, 0.01% ≤ y ≤ 0.3%, 0.01% ≤ z ≤ 0.3%; the doped lithium-rich cobaltate: D50 = 3 - 10 μm, (D90 - D10) / D50 = 0.5 - 2.5, BET is 0.1 - 1 m 2 / g; Preferably, x+y+z≤1.2%; Preferably, the doped lithium-rich cobaltate has a D50 of 4-7 μm, (D90-D10) / D50 = 1.0-1.5, and a BET of 0.2-0.6 m 2 / g.

3. The cathode lithium supplement agent according to claim 1, characterized in that, The molecular formula of the spinel lithium cobaltate is Li m Co n O k , where: 0.8 ≤ m ≤ 1.2, n is 1 or 2, and k = 2n; Preferably, the molecular formula of the spinel lithium cobalt oxide is LiCo2O4 or low temperature phase LiCoO2.

4. The cathode lithium supplement according to claim 1, wherein The doped lithium-rich cobaltate has a tetragonal anti-fluorite structure, belonging to the P42 / nmc space group, and the unit cell parameters a and c respectively satisfy: The spinel cobaltate belongs to the Fd3m space group; Preferably, the lattice parameter a of the doped lithium-rich cobaltate is and c is 5. The cathode lithium supplement according to claim 1, characterized in that The coating amount of the shell is 0.1wt%-3wt% of the core.

6. A method for preparing a cathode lithium supplement as described in any one of claims 1-5, characterized in that, The steps are as follows: S1, preparing aluminum source, magnesium source, zirconium source, lithium source and cobalt source according to a specific stoichiometric ratio and mixing them evenly, and then solid-phase sintering and crushing them at high temperature in an inert atmosphere to obtain a primary crushed material; S2, mixing the primary crushed material with the cobalt source and the lithium source in a specific stoichiometric ratio and then sintering them in a low-temperature solid phase in an inert atmosphere; S3. Crush and sieve the product from the previous step.

7. The preparation method of the cathode lithium supplement agent according to claim 6, characterized in that, In step S1, the temperature of high-temperature solid-phase sintering is 500-1000°C, the time is 4-20h, and the amount of the substance actually added to the lithium source exceeds the theoretical amount of the substance added by 0.1%-5%; in step S2, the temperature of low-temperature solid-phase sintering is 300-800°C, the time is 4-16h, and the amount of the substance actually added to the lithium source exceeds the theoretical amount of the substance added by 0.1%-4%; Preferably, the temperature of high-temperature solid-phase sintering in step S1 is 700-800°C, the time is 8-16h, and the amount of the substance actually added to the lithium source exceeds the theoretical amount of the substance added by 1%-3%; Preferably, the temperature of low-temperature solid-phase sintering in step S2 is 400-600° C., the time is 8-16 hours, and the amount of the substance actually added to the lithium source exceeds the theoretical amount of the substance added by 1%-2.5%; Preferably, the particle size D50 of the cobalt source in step S1 and step S2 is 2-9 μm, the cobalt source in S1 is aluminum-doped cobalt tetroxide, and the cobalt source in S2 is selected from one or more of cobalt tetroxide, cobaltous oxide, cobalt hydroxide, cobalt oxyhydroxide, and cobalt carbonate; Preferably, the lithium sources in step S1 and step S2 are the same or different, and are selected from one or more of lithium oxide, lithium peroxide, lithium hydroxide, and lithium carbonate; Preferably, the particle size of the magnesium source in step S1 is not greater than 200 nm, and is selected from one or more of magnesium oxide, magnesium hydroxide, magnesium carbonate, basic magnesium carbonate, and magnesium oxalate; Preferably, the particle size of the zirconium source in step S1 is not greater than 200 nm, and is selected from one or more of zirconium dioxide, zirconium hydroxide, zirconium carbonate, basic zirconium carbonate, and zirconium oxalate.

8. A positive electrode sheet, characterized in that, The active material thereon includes a positive electrode active material and a positive electrode lithium supplement as described in any one of claims 1 to 7, wherein the positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, and lithium manganese iron phosphate.

9. The positive electrode sheet according to claim 8, wherein, The positive electrode active material is high voltage lithium cobalt oxide, and the positive electrode lithium supplement agent is added in an amount of 0.1%-10% in the positive electrode slurry; Preferably, the positive electrode active material is lithium cobalt oxide with a voltage of ≥4.5V, and the positive electrode lithium supplement agent is added in an amount of 0.5%-3% in the positive electrode slurry.

10. A lithium battery, characterized in that, Comprising a negative electrode sheet and a positive electrode sheet as claimed in claim 8 or 9; Preferably, the negative electrode plate is a silicon-based negative electrode plate.

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