A material with an ultra-high lithium content and a self-complementary lithium composite cathode material

Abstract

The present invention relates to a material with an ultra-high lithium content and a self-complementary lithium composite cathode material. The chemical formula of the material with an ultra-high lithium content is Li5M x A 1‑x O4 or Li8M x B 1‑x O6. The self-complementary lithium composite cathode material is such that the surface of the cathode material is uniformly and densely coated with the material with an ultra-high lithium content. By forming a uniformly and densely coated layer of a high-lithium-content compound on the surface of the cathode particles, the present invention realizes the function of self-complementary lithium in the cathode material itself, compensates for the consumption of lithium in the battery, and prolongs the cycle life of the battery; in addition, after the high-lithium-content layer on the surface plays the role of complementary lithium, it can be transformed into a dense and firm surface protection layer, thereby avoiding further side reactions between the cathode and the electrolyte and enhancing the cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a material with an ultra-high lithium content and a self-complementary lithium composite cathode material. Background Art

[0002] Lithium-ion batteries can convert chemical energy and electrical energy into each other to achieve efficient energy storage and utilization. The popularization of current various consumer electronic products is inseparable from the successful application of lithium-ion batteries. Moreover, with the development of their energy density, they are even gradually applied to large-scale electric devices such as electric vehicles, which will greatly reduce exhaust emissions and promote the development of a low-carbon and environmentally friendly world. A wider application range requires lithium-ion batteries to have a higher energy density and excellent electrochemical performance. Among the three major components of a lithium-ion battery, namely the cathode, anode, and electrolyte, the cathode is a key factor restricting the improvement of the energy density of lithium-ion batteries. Especially in modern lithium-ion battery configurations, all lithium is provided by the cathode. However, during the electrochemical cycling process, some consumption of the active lithium in the battery is inevitable. For example, a solid electrolyte interface phase is formed on the surface of the anode side, and side reactions occur with the electrolyte to form dead lithium, etc. The loss of active lithium in these batteries will lead to capacity attenuation. In addition, side reactions also occur between the surface of the cathode material and the electrolyte, which destroys the surface structure of the particles, increases the ion transport impedance, and reduces the battery life.

[0003] In the prior art, two routes of lithium supplementation and coating are respectively adopted to address the above problems. Among them, lithium supplementation usually involves adding some lithium supplementation agents such as lithium powder, inorganic binary lithium salts, lithium-transition metal-oxides, etc. to the cathode or anode. For example, Patent CN113991101A discloses a method of adding a lithium-rich manganese-based material to a lithium iron phosphate cathode sheet for lithium supplementation, and a step current and a constant voltage and current limiting combination method are used to pre-charge and form the battery to achieve lithium supplementation. Patent CN113921803A discloses a lithium supplementation method, which adds Li8SnO6 to the cathode slurry and is compatible with the existing production process, and can improve the battery capacity and cycle life. However, simply adding a lithium supplementation agent cannot protect the cathode. Coating generally involves constructing a protective layer on the surface of the cathode to avoid side reactions between the cathode and the electrolyte and improve the surface stability of the material, such as the methods disclosed in Patent CN114122377A and CN113830846A. However, the commonly used ones are electrochemically inert inorganic compounds, which will reduce the material capacity and increase the interfacial impedance.

[0004] The literature (ACS Omega 2020, 5, 16912) reported that the Co-doped Li5AlO4 cathode material was prepared by ball milling Li5AlO4 and lithium cobaltate at a molar ratio of 1:1. However, it only simply mixed Li5AlO4 and lithium cobaltate to achieve Co doping, and finally used Co-doped Li5AlO4 as the cathode material to test the electrochemical performance, which could not achieve stable cycling, and the voltage range was low, and a large amount of lithium cobaltate in the system was hardly utilized. Summary of the Invention

[0005] In view of the above problems, the purpose of the present invention is to provide a class of ultra-high lithium content materials and a self-complementary lithium composite cathode material with a layer of the ultra-high lithium content material coated on its surface, as well as their preparation methods. The composite cathode prepared by the present invention has a higher first-cycle charge specific capacity and cycling stability. The present invention constructs a dense and uniform material with ultra-high lithium content on the surface of the cathode, which can release lithium ions during the first charging process. In addition to compensating for the lithium ions consumed by the positive and negative electrode interface reaction, a certain amount of capacity can also be provided. At the same time, the coating layer can be transformed into a dense and firm protective layer after delithiation, avoiding further side reactions on the surface of the cathode and improving the electrochemical performance of the cathode.

[0006] The purpose of the present invention is achieved by the following technical solutions:

[0007] The first purpose of the present invention is to provide an ultra-high lithium content material, which is characterized in that the chemical formula is Li5M x A 1-x O4 or Li8M x B 1-x O6, where the doping element M is one or more of Co, Ni, Fe, Cu, Zn, B, Mg, Ga, Ge, Mn, Ti, Cr, La, Ce, W, Ta, Sn, Mo, Nb, Y, Zr, 0.01 ≤ x ≤ 0.1; the main metal element A is at least one of Al and Ga, and the main metal element B is at least one of Sn or Zr.

[0008] Preferably, M is Co or Ce, and 0.03 ≤ x ≤ 0.05.

[0009] The second purpose of the present invention is to provide a self-complementary lithium composite cathode material, in which the surface of the cathode material is uniformly and densely coated with the above ultra-high lithium content material. Among them, the lithium element of the ultra-high lithium content material accounts for 30-70% of the total lithium element in the self-complementary lithium composite cathode material, preferably 40-50%. The lithium element in the composite cathode material comes from two parts, one part comes from the ultra-high lithium content material of the coating layer, and the other part comes from the cathode material to be coated.

[0010] Furthermore, the coating layer of the composite cathode material has Li5Mx A 1-x O4 or Li8M x B 1-x The lattice spacing of O6, such as or This lattice spacing confirms that the chemical structure of the coating layer is Li5M x A 1-x O4 or Li8M x B 1-x O6.

[0011] Preferably, the positive electrode material includes lithium cobaltate, lithium iron phosphate, lithium nickel manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate. High-nickel materials are preferred, including but not limited to: LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.83 Co 0.11 Mn 0.06 O2, LiNi 0.9 Co 0.06 Mn 0.04 At least one of O2.

[0012] Preferably, the thickness of the coating layer of the ultra-high lithium content material is 20-40 nm.

[0013] The third object of the present invention is to provide a preparation method of the above self-complementary lithium composite positive electrode material, including the following steps:

[0014] (S1) First, the Li element precursor, the A or B element precursor, the doped element M precursor and the chelating agent are uniformly dispersed in water in a certain proportion, and then the positive electrode material precursor is added thereto and dispersed evenly;

[0015] (S2) The liquid dispersion system obtained in step (S1) is placed in an oil bath, the pH of the system is adjusted to 4-6, and it is stirred and heated with an open mouth until the system gels, and then it is dried;

[0016] (S3) The dried system obtained in S2 is ground and refined, and the lithium-supplemented composite positive electrode material is obtained after sintering.

[0017] Furthermore, the amount of water added in step (S1) makes the solid content of the dispersion system 1-5%, preferably 2-3%.

[0018] Further, in (S1), the precursors of various metal elements are at least one of water-soluble metal alkoxides, metal organic acid salts, and complexes of organic substances and metals. In a specific embodiment of the present invention, the precursor of Li element is selected from at least one of lithium acetate, lithium oxalate, and lithium nitrate; the precursor of element A or B is an alkoxide of element A or B, specifically selected from isopropoxides of metal A or B, such as aluminum isopropoxide, gallium isopropoxide, tin isopropoxide, and zirconium isopropoxide; the precursor of the doping element M is a water-soluble M metal compound, specifically selected from acetates, oxalates, acetylacetonates, and nitrates; such as cobalt acetate, nickel acetate, manganese acetate, ferrous oxalate, copper oxalate, cerium nitrate, yttrium nitrate, etc.; the precursor of the positive electrode is a hydroxide of the positive electrode material, such as Ni 0.5 Co 0.2 Mn 0.3 (OH)2, Ni 0.6 Co 0.2 Mn 0.2 (OH)2, Ni 0.8 Co 0.1 Mn 0.1 (OH)2; the chelating agent is a polycarboxylic acid, such as citric acid, maleic acid, and cyclic polyamine polycarboxylic acid compounds.

[0019] Further, in (S1), the chelating agent is a compound prepared by mixing citric acid and a cyclic polyamine polycarboxylic acid compound in a mass ratio of 4-7:1; the cyclic polyamine polycarboxylic acid compound is selected from at least one of 1,4,7,10-tetraazacyclododecane-N-tetraacetic acid, 1,5,8,11-tetraazacyclotridecane-N-tetraacetic acid, 1,5,8,12-tetraazacyclotetradecane-N-tetraacetic acid, and 1,4,7,10,13,16-hexaazacyclooctadecane-N-hexaacetic acid.

[0020] The inventors unexpectedly found that using the compound of citric acid and cyclic polyamine polycarboxylic acid as a chelating agent can enable elements A or B and M to nucleate uniformly and slowly on the surface of the positive electrode precursor, while avoiding the separate nucleation and growth of the above elements in the system, maintaining the dispersion of the positive electrode precursor particles, so that the thickness of the coating layer can be adjusted according to the addition amount. Furthermore, the ultra-high lithium content material can be uniformly and densely coated on the positive electrode material, realizing the self-lithium compensation function of the positive electrode material and extending the cycle life of the battery; and a dense and firm surface protection layer can be formed after de-lithiation, thus avoiding further side reactions between the positive electrode and the electrolyte and further enhancing the cycle stability.

[0021] (S1), the addition amounts of the Li element precursor, the A or B element precursor, and the doping element M precursor make the feeding ratio of each element satisfy the chemical formula Li5M x A 1-x O4 or Li8M x B 1-xO6. In addition, since Li in the Li element precursor also needs to form a lithium-containing cathode material with the cathode material precursor, the feeding ratio of the Li element precursor and the cathode precursor should also satisfy the chemical formula LiNi x Co y Mn 1-x-y O2. Considering the loss of lithium element caused by a certain degree of lithium volatilization in the subsequent process (mainly forming a material with extremely high lithium content Li5M x A 1-x O4 or Li8M x B 1-x O6), the Li element precursor is generally about 10% in excess of the stoichiometric ratio, such as 5 - 15% in excess, preferably 8 - 12% in excess.

[0022] Therefore, for the material with extremely high lithium content in the coating layer of the composite cathode material with the chemical formula Li5M x A 1-x O4, the dosages of the Li element precursor, the A element precursor, the doping element M precursor and the cathode material precursor satisfy that the molar ratios of element Li, element A, element M and the cathode material precursor are 8 - 16:0.90 - 0.99:0.01 - 0.1:2.5 - 10.5. Among them, the amount of substance of the cathode material precursor is calculated according to the total sum of the metal active components therein. For example, for a nickel-cobalt-manganese (aluminum) cathode material, its amount of substance is the sum of Ni, Co, Mn and Al (if present); and, the ratio of the amount of substance of the Li element precursor minus the sum of the amounts of substance of the cathode material precursor, element A and element M is 5.3 - 5.7:1, preferably 5.4 - 5.5:1.

[0023] For the material with extremely high lithium content in the coating layer of the composite cathode material with the chemical formula Li8M x B 1-x O6, the dosages of the Li element precursor, the B element precursor, the doping element M precursor and the cathode material precursor satisfy that the molar ratios of element Li, element B, element M and the cathode material precursor are 12 - 26:0.90 - 0.99:0.01 - 0.1:3.5 - 17.5, preferably 16 - 21:0.90 - 0.99:0.01 - 0.1:8 - 12; and, the ratio of the amount of substance of the Li element precursor minus the sum of the amounts of substance of the cathode material precursor, element B and element M is 8.5 - 9:1, preferably 8.7 - 8.8:1.

[0024] Those skilled in the art should be able to understand that although the feeding ratios of the elements in the raw materials often have a certain difference from the molar ratios of the elements in the final product, this difference is not significant. Except for about 10% consumption of Li, for other metals except Li, the feeding ratio of the raw materials can be approximately regarded as the molar ratio of the elements in the product.

[0025] The amount of the chelating agent used is not particularly limited, and is generally 2-4 times, such as 3-3.5 times, the total amount of element B and element M.

[0026] Furthermore, the oil bath temperature of (S2) is 60-90°C, the drying is 80-150°C, and the drying time is 10-15h. The drying is not particularly limited, and it can be fully dried by conventional methods in the art, such as vacuum drying and oven drying.

[0027] Furthermore, in (S3), grinding is performed using an agate mortar until the positive electrode precursor particles are dispersed, and the calcination atmosphere is at least one of air, oxygen, nitrogen, and carbon dioxide, preferably an oxygen atmosphere.

[0028] Furthermore, in (S3), the sintering is divided into two stages: pre-sintering and secondary sintering. The pre-sintering is calcined at 300-500°C for 3-7h, and the secondary sintering is sintered at 700-900°C for 8-15h, followed by cooling. The heating rate is 5-15°C·min -1 , the cooling process is natural cooling.

[0029] The fourth object of the present invention is to provide a lithium battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is the above-mentioned self-replenishing lithium composite positive electrode material.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. By forming a uniform and dense high-lithium content compound coating layer on the surface of the positive electrode particles, the modified positive electrode material can have its own lithium replenishment function, compensate for the consumption of lithium in the battery, and extend the cycle life of the battery; in addition, after the high lithium content layer on the surface plays the role of lithium replenishment, it can be converted into a dense and strong surface protective layer, thereby avoiding further side reactions between the positive electrode and the electrolyte and enhancing the cycle stability.

[0032] Second, by doping elements to improve the electronic conductivity of the surface high lithium content layer, it is possible to fully utilize its capacity, reduce the lithium desorption potential, and increase the Li + conductivity and reduce the positive electrode interface impedance.

[0033] 3. Compared with the common lithium supplementation and coating methods, the method of the present invention can combine them into one, and the effect is flexible and adjustable, which has important practical value. The obtained surface ultra-high lithium content composite positive electrode can operate stably in lithium-ion batteries for a long time due to its own functionality.

[0034] IV. Through the combination of specific chelating agents, the present invention can enable the raw materials to nucleate uniformly and slowly on the surface of the cathode precursor during the gelation process, avoiding the separate nucleation and cross-linking of the raw materials, so that a uniform coating of the high-lithium compound precursor is formed on the surface of the cathode precursor. After further calcination, a uniform and dense coating layer is formed on the surface of the cathode material, which is more conducive to the electrochemical performance of the cathode material. Description of the Drawings

[0035] Figure 1 SEM image of the cathode material with a super-high lithium content on the surface prepared in Example 1;

[0036] Figure 2 TEM image of the surface region of the cathode material with a super-high lithium content on the surface prepared in Example 1;

[0037] Figure 3 TEM image of the surface region of the cathode material with a super-high lithium content on the surface prepared in Example 7;

[0038] Figure 4 TEM image of the surface region of the cathode material with a super-high lithium content on the surface prepared in Example 8;

[0039] Figure 5 Charge-discharge curve of the cathode material with a super-high lithium content on the surface prepared in Example 1 at a rate of 0.1C;

[0040] Figure 6 Discharge specific capacity retention rate of the cathode material with a super-high lithium content on the surface prepared in Example 1 at a rate of 1C. Detailed Description of the Invention

[0041] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments. Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0042] The experimental methods described in the following embodiments are all conventional methods unless otherwise specified; the reagents and materials described, unless otherwise specified, can all be obtained from commercial channels.

[0043] The ternary cathode material with a super-high lithium content on the surface for lithium-ion batteries was characterized by a scanning electron microscope (S-4800). The coating layer on the surface of the cathode material for lithium-ion batteries was analyzed by a transmission electron microscope (JEM-2100F).

[0044] Example 1

[0045] First, lithium acetate, aluminum isopropoxide, cobalt acetate and citric acid were dissolved in water, sonicated, stirred and dispersed evenly, and then Ni was added 0.8Co 0.1 Mn 0.1 (OH)2 cathode precursor, the amount of water added makes the solid content of the dispersion system about 2%. The molar ratio of lithium acetate, aluminum isopropoxide, cobalt acetate, citric acid and the cathode precursor is 8:0.97:0.03:3:2.5. Place the above dispersion system in an oil bath at 65 °C and stir. Adjust the pH to 5 with dilute nitric acid, continue stirring until gelation occurs, dry at 80 °C for 12 h, and then grind into powder. Sinter the powder in a muffle furnace, with a heating rate of 5 °C·min -1 to heat up to 450 °C, hold for 4 hours, take out and grind, then reload, and heat up to 870 °C at a heating rate of 10 °C·min -1 , hold for 12 hours, and cool down naturally. Grind the product with an agate mortar until the cathode particles are dispersed separately to obtain a cathode material with a super-high lithium content on the surface. Calculated according to the loss of about 10% of Li when forming the super-high lithium content material, it can be known that in the composite cathode material, the Li in the super-high lithium content material as the coating layer accounts for about 66.7% of the composite cathode material. 0.03 Al 0.97 O4.

[0046] Figure 1 Figure 184 is the scanning electron microscope image of the cathode with a super-high lithium content on the surface prepared in Example 1. It can be seen that there is a relatively uniform coating layer on the particle surface. Figure 2 Figure 187 is the transmission electron microscope image of the surface area of the ternary cathode with a super-high lithium content on the surface prepared in Example 1. It can be seen that there is a coating layer with a thickness of about 20 nm distributed on the particle surface. By observing the lattice spacing of the lattice fringes of the surface coating layer through transmission electron microscopy, it can be confirmed that the lithium-containing compound covering the front surface is Li5Co 0.03 Al 0.97 O4 with the same lattice structure as Li5AlO4.

[0047] Example 2

[0048] Other conditions are the same as those in Example 1, except that when feeding raw materials, the molar ratio of lithium acetate, aluminum isopropoxide, cobalt acetate, citric acid and the cathode precursor is 10.5:0.97:0.03:3:5. Calculated, in the composite cathode material, the Li in the super-high lithium content material as the coating layer accounts for about 50% of the composite cathode material.

[0049] Example 3

[0050] Other conditions are the same as those in Example 1, except that when feeding raw materials, the molar ratio of lithium acetate, aluminum isopropoxide, cobalt acetate, citric acid and the cathode precursor is 13:0.97:0.03:3:7.5. Calculated, in the composite cathode material, the Li in the super-high lithium content material as the coating layer accounts for about 40% of the composite cathode material.

[0051] Example 4

[0052] Other conditions are the same as those in Example 1, except that when feeding raw materials, the molar ratio of lithium acetate, aluminum isopropoxide, cobalt acetate, citric acid and the cathode precursor is 15.5:0.97:0.03:3:10. It can be calculated that in the composite cathode material, Li in the ultra-high lithium content material as the coating layer accounts for about 33.3% of the composite cathode material.

[0053] Example 5

[0054] Other conditions are the same as those in Example 2, except that the molar ratio of lithium acetate, aluminum isopropoxide, cobalt acetate, citric acid and the cathode precursor is 10.5:0.95:0.05:3:5. A composite cathode material with a nickel-cobalt-manganese ternary cathode material coated with an ultra-high lithium content material is obtained, where the ultra-high lithium content material is Li5Co 0.05 Al 0.95 O4. It can be calculated that in the composite cathode material, Li in the ultra-high lithium content material as the coating layer accounts for about 50% of the composite cathode material.

[0055] Example 6

[0056] Other conditions are the same as those in Example 2, except that aluminum isopropoxide is replaced with an equimolar amount of gallium nitrate. It can be calculated that in the composite cathode material, Li in the ultra-high lithium content material as the coating layer accounts for about 50% of the composite cathode material.

[0057] Example 7

[0058] First, dissolve lithium acetate, zirconium n-propoxide, cerium nitrate and citric acid in water, sonicate, stir to disperse evenly, and then add Ni 0.8 Co 0.1 Mn 0.1 (OH)2 cathode precursor and sonicate to dissolve. The amount of water added makes the solid content of the dispersion system about 2%. The molar ratio of lithium acetate, zirconium n-propoxide, cerium nitrate, citric acid and the cathode precursor is 20.8:0.97:0.03:3:12; place the above dispersion system in an oil bath at 65°C and stir, adjust the pH to 6 with dilute nitric acid, continue stirring until gelation occurs, dry at 80°C for 12 h, and then grind into powder. Sinter the powder in a muffle furnace, with a heating rate of 5°C·min -1 , heat up to 450°C, hold for 4 hours, take out and grind, then reload, and heat up to 850°C at a heating rate of 10°C·min -1 , hold for 12 hours, cool down naturally, and grind the product with an agate mortar until the cathode particles are dispersed separately to obtain a surface ultra-high lithium content cathode material.

[0059] Figure 3Transmission electron microscopy image of the surface ultra-high lithium content cathode prepared in Example 7. According to the lattice spacing of the coating layer, it can be confirmed that the lithium-containing compound covering the front surface is Li8Ce with the same lattice structure as Li8ZrO6 0.03 Zr 0.97 O6.

[0060] It can be calculated that in the composite cathode material, the Li in the ultra-high lithium content material Li8Ce 0.03 Zr 0.97 O6 as the coating layer accounts for about 40% of the composite cathode material.

[0061] Example 8

[0062] Other conditions are the same as in Example 7, except that the molar ratio of lithium acetate, zirconium propoxide, cerium nitrate, citric acid and the cathode precursor is 16.8:0.97:0.03:3:8. The Li in the ultra-high lithium content material as the coating layer accounts for about 50% of the composite cathode material.

[0063] Example 9

[0064] Other conditions are the same as in Example 2, except that the chelating agent is a compound of citric acid and 1,4,7,10-tetraazacyclododecane-N-tetraacetic acid, and the chelating agent is dissolved in 80% ethanol.

[0065] Figure 4 Transmission electron microscopy image of the surface region of the surface ultra-high lithium content ternary cathode prepared in Example 9, it can be seen that it has a more uniform and dense coating layer than in Example 2.

[0066] Example 10

[0067] Other conditions are the same as in Example 2, except that the chelating agent is a compound of citric acid and 1,5,8,12-tetraazacyclotetradecane-N-tetraacetic acid, and the chelating agent is dissolved in 80% ethanol.

[0068] Comparative Example 1

[0069] Ultrasonically stir and uniformly disperse the Ni 0.8 Co 0.1 Mn 0.1 (OH)2 cathode precursor in ethanol. Place the above dispersion system in an oil bath at 65 °C and stir for 3 hours, dry at 80 °C for 12 h, and then add a lithium salt and grind according to the molar ratio of precursor: lithium hydroxide of 1:0.5. Sinter the powder in a muffle furnace, with a heating rate of 5 °C·min -1 , heat up to 450 °C, hold for 4 hours, take out and grind and then reload, and heat up to 870 °C at a heating rate of 10 °C·min -1 , hold for 12 hours, and cool naturally. Grind the product to obtain the comparative cathode material.

[0070] Application Example

[0071] The ternary lithium-ion battery cathode material, conductive carbon black, and polyvinylidene fluoride binder obtained from the above examples and comparative examples were mixed at a mass ratio of 8:1:1 to form a slurry, which was uniformly coated on a carbon-coated aluminum foil current collector to obtain a positive electrode sheet. A lithium metal sheet was used as the negative electrode, a polypropylene microporous membrane (Celgard 2400) was used as the separator, and 1 mol / L LiPF6 (the solvent was a mixed solution of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) at a volume ratio of 1:1:1) was used as the electrolyte. A CR2032 type button battery was assembled in a glove box under argon protection. The assembled battery was subjected to constant current charge and discharge tests on a BlueTEC charge and discharge tester, with a voltage range of 3 - 4.3 V and a test temperature of 25 °C. The discharge specific capacity was tested at a rate of 0.1 C (equivalent to 20 mA g -1 ), and the cycle stability of the cathode material was tested at a rate of 1 C. The results are shown in Table 1 below.

[0072] Figure 5 The charge and discharge curve of the lithium-ion battery assembled with the surface ultra-high lithium content composite cathode obtained in Example 1 at 0.1 C is shown. It can be seen that after surface modification, the initial charge specific capacity of the cathode material can reach 259.5 mAh g -1 , and the discharge specific capacity remains at 203.4 mAh g -1 . This shows that the surface ultra-high lithium content layer effectively played its capacity during the first charge, while the discharge was still at a normal level, indicating that the ultra-high lithium content layer provided additional lithium ions for the irreversible loss on the negative electrode side. Figure 6 The discharge specific capacity retention rate diagram of the surface ultra-high lithium content cathode material prepared in Example 1 at a rate of 1 C is shown, indicating that the modified material surface has good cycle stability due to the formation of a strong interfacial layer after activation.

[0073] Table 1

[0074]

[0075]

[0076] From the description of the accompanying drawings and the data in Table 1, it can be seen that the surface ultra-high lithium content cathode material provided by the present invention exhibits excellent electrochemical performance. The surface ultra-high lithium content layer of the material provides additional capacity during the first charge to compensate for irreversible losses and improves cycle stability. In addition, the dense interfacial layer formed after de-lithiation of the surface ultra-high lithium content layer can effectively enhance the cycle stability of the cathode, which is of great significance for the further development of future cathode materials.

[0077] By comparing Example 2 with Examples 9 and 10, it can be seen that using the compound of citric acid and cyclic polyamino polycarboxylic acid as a chelating agent can further enhance the cycle stability of the cathode material.

Claims

1. A preparation method of a self-complementary lithium composite cathode material, characterized in that, It includes the following steps: (S1) Uniformly disperse the Li element precursor, A or B element precursor, doped element M precursor, and chelating agent in water in a certain proportion, and then add the cathode material precursor thereto and disperse evenly; the chelating agent is a compound prepared by mixing citric acid and cyclic polyamino polycarboxylic acid compound in a mass ratio of 4-7:1; the cyclic polyamino polycarboxylic acid compound is selected from at least one of 1,4,7,10-tetraazacyclododecane-N-tetraacetic acid, 1,5,8,11-tetraazacyclotridecane-N-tetraacetic acid, 1,5,8,12-tetraazacyclotetradecane-N-tetraacetic acid, 1,4,7,10,13,16-hexaazacyclooctadecane-N-hexaacetic acid; (S2) Place the liquid dispersion system obtained in step (S1) in an oil bath, adjust the pH of the system to 4-6, stir and heat it with an open mouth until gelation occurs in the system, and then dry it; (S3) Grind and refine the dried system obtained in S2, and obtain a self-complementary lithium composite cathode material after sintering; The self-complementary lithium composite cathode material is that the surface of the cathode material is uniformly and densely coated with a material with a very high lithium content; wherein, the lithium element of the material with a very high lithium content accounts for 30-70% of the total lithium element in the self-complementary lithium composite cathode material; the material with a very high lithium content has the chemical formula of Li5M x A 1-x O4 or Li8M x B 1-x O6, where the doping element M is Co or Ce, 0.03 ≤ x ≤ 0.05; the main metal element A is at least one of Al and Ga, and the main metal element B is at least one of Sn and Zr.

2. The preparation method according to claim 1, characterized in that, The lithium element of the ultra-high lithium content material accounts for 40-50% of the total lithium element in the self-complementary lithium composite cathode material.

3. The preparation method according to claim 1, characterized in that, The coating layer thickness of the ultra-high lithium content material is 20-40 nm.

4. The preparation method according to claim 1, characterized in that, The coating layer of the composite cathode material has a Li5AO4-type lattice spacing within 2.65±0.02 Å or a Li8BO6-type lattice spacing within 4.56±0.02 Å.

5. The preparation method according to claim 1, characterized in that, The cathode material includes lithium cobaltate, lithium iron phosphate, lithium nickel manganate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate.

6. The preparation method according to claim 5, characterized in that, The positive electrode material includes LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.83 Co 0.11 Mn 0.06 O2, LiNi 0.9 Co 0.06 Mn 0.04 and at least one of O2.

7. The preparation method according to claim 1, characterized in that, In step (S1), the precursors of various metal elements are at least one of water-soluble metal alkoxides, metal organic acid salts, and complexes of organic substances and metals.

8. The preparation method according to claim 7, characterized in that, The Li element precursor is selected from at least one of lithium acetate, lithium oxalate, and lithium nitrate; the A or B element precursor is an alkoxide of element A or B; the doped element M precursor is a water-soluble M metal compound; the cathode material precursor is a hydroxide of the cathode material.

9. The preparation method according to claim 8, characterized in that, The precursor of element A or B is the isopropoxide of metal A or B; the precursor of the doping element M is selected from acetate, oxalate, acetylacetonate, and nitrate; the precursor of the cathode material is selected from Ni 0.5 Co 0.2 Mn 0.3 (OH)2, Ni 0.6 Co 0.2 Mn 0.2 (OH)2, Ni 0.8 Co 0.1 Mn 0.1 (OH)2.

10. The preparation method according to claim 9, characterized in that, The doped element M precursor is selected from cobalt acetate, nickel acetate, manganese acetate, ferrous oxalate, copper oxalate, cerium nitrate, and yttrium nitrate.

11. The preparation method according to claim 9, characterized in that, The alkoxide of element A or B is selected from aluminum isopropoxide, gallium isopropoxide, tin isopropoxide, and zirconium isopropoxide.

12. The preparation method according to claim 1, characterized in that, The chemical formula of the material with an ultra-high lithium content in the coating layer of the composite cathode material is Li5M x A 1-x When it is O4, in step (S1), the dosages of the Li element precursor, the A element precursor, the doped element M precursor, and the cathode material precursor satisfy that the molar ratios of the elements Li, A, M, and the cathode material precursor are 8-16: 0.90-0.99: 0.01-0.1: 2.5-10.5; and, the ratio of the amount of the Li element precursor substance minus the sum of the amounts of the cathode material precursor substance, the element A, and the element M substance is 5.3-5.7: 1; The chemical formula of the material with an ultra-high lithium content in the coating layer of the composite cathode material is Li8M x B 1-x When it is O6, the dosages of the Li element precursor, B element precursor, doping element M precursor and cathode material precursor satisfy that the molar ratios of element Li, element B, element M and the cathode material precursor are 12 - 26: 0.90 - 0.99: 0.01 - 0.1: 3.5 - 17.5; and, the ratio of the amount of substance of the Li element precursor minus the amount of substance of the cathode material precursor to the total amount of substance of element B and element M is 8.5 - 9:

1.

13. The preparation method according to claim 12, characterized in that, The chemical formula of the material with an ultra-high lithium content in the coating layer of the composite cathode material is Li5M x A 1-x When it is O4, the ratio of the amount of substance of the Li element precursor minus the amount of substance of the cathode material precursor to the total amount of substance of element A and element M is 5.4 - 5.5:1; The chemical formula of the material with an ultra-high lithium content in the coating layer of the composite cathode material is Li8M x B 1-x When it is O6, the ratio of the amount of substance of the Li element precursor minus the amount of substance of the cathode material precursor to the total amount of substance of element B and element M is 8.7 - 8.8:

1.

14. A lithium battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is the self-complementary lithium composite cathode material prepared by the preparation method according to any one of claims 1-13.

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