Modified positive electrode precursor and preparation method and application thereof

Abstract

The invention provides a modified positive electrode precursor as well as a preparation method and application thereof. The modified positive electrode precursor comprises a titanium-doped core and a niobium-doped coating layer arranged on the titanium-doped surface, the interior of the titanium-doped inner core is of a hollow structure. The modified positive electrode precursor has the structure of the titanium-doped hollow core and the niobium-doped coating layer, the structural stability of the hollow core can be ensured by uniform doping of titanium, a buffer space is provided for lithium ion intercalation / deintercalation in the charging and discharging process under the condition of ensuring the structural stability, the risk of particle breakage is reduced, and the performance of the lithium ion battery is improved. The lithium ion diffusion distance can be shortened, the rate capability can be improved, niobium is uniformly doped in the coating layer, niobium ions generate Li-Nb-O spinel phases on the surfaces of particles, electrolyte decomposition and transition metal dissolution are inhibited, meanwhile, rapid transmission of surface Li < + > can be promoted, the interface impedance can be reduced, and the capacity of the material can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials and relates to a modified positive electrode precursor and a preparation method and application thereof. Background Art

[0002] The continuous development of new energy battery materials has led to an increasing variety of precursor material synthesis options, morphology control, and structural control. To meet the electrical performance requirements of different cathode materials, the requirements for precursor synthesis are also ever-changing. As the core raw material for preparing cathode materials, the structure and performance of cathode precursors directly affect the quality of the final cathode material. With the increasing performance requirements for secondary batteries in fields such as electric vehicles and energy storage systems, the development of cathode precursors with high capacity and long cycle life has become a key research direction in the industry.

[0003] Hollow-structured cathode materials offer multiple advantages in energy storage systems such as lithium-ion batteries, sodium-ion batteries, and lithium-sulfur batteries. These advantages include a hollow interior that provides a buffer for volume changes in the active material during charge and discharge, significantly inhibiting structural collapse of the electrode material and reducing the risk of particle breakage, thereby extending cycle life. Furthermore, the hollow structure accelerates lithium-ion transport by increasing specific surface area and shortening diffusion distances. While preparing hollow-structured cathode materials from hollow-structured precursors is an effective approach, existing technologies present at least one of the following challenges: The resulting hollow-structured precursors suffer from poor structural stability, complex and costly preparation processes, and difficulty in industrialization.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a modified positive electrode precursor and its preparation method and application. The modified positive electrode precursor of the present invention has a structure of a titanium-doped hollow core and a niobium-doped coating layer. Uniform titanium doping can ensure the structural stability of the hollow core, provide a buffer space for lithium ion insertion / ejection during the charge and discharge process while ensuring structural stability, reduce the risk of particle breakage, shorten the lithium ion diffusion distance, and improve the rate performance; niobium is uniformly doped in the coating layer, and niobium ions form a Li-Nb-O spinel phase on the particle surface, which inhibits the decomposition of the electrolyte and the dissolution of transition metals while promoting the surface Li + Fast transmission, reduced interface impedance, and increased material capacity.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a modified positive electrode precursor, comprising a doped core and a doped coating layer disposed on a surface of the doped core;

[0008] The interior of the doped core is a hollow structure;

[0009] The doped core contains titanium element, and the doped cladding layer contains niobium element.

[0010] Other doping metal elements may also be provided in the core and coating layer of the modified positive electrode precursor of the present invention, but titanium is only doped in the core, and niobium is only doped in the coating layer.

[0011] In the modified cathode precursor of the present invention, the hollow core structure provides stress buffer space for lithium ion insertion / ejection during charge and discharge, reducing the risk of particle breakage, and the thin-walled hollow core structure can shorten the Li + The diffusion distance of the core is shortened, improving rate performance. However, the hollow structure of the core results in low structural stability. The present invention uniformly dopes the core with titanium, allowing titanium to preferentially occupy transition metal sites, stabilize the lattice structure, and inhibit phase transitions during cycling. The strong Ti-O bond energy of titanium ions enhances the stability of the core oxygen framework and reduces oxygen loss under high voltage. Niobium doping in the coating significantly improves its stability and passivates side reactions at the interface. Ti stabilizes the bulk structure, while Nb inhibits surface degradation. The synergistic effect of the two significantly improves the capacity and cycling performance of the positive electrode material.

[0012] Preferably, the chemical formula of the doped core includes M x Ti y O2, M includes any one of nickel, cobalt or manganese or a combination of at least two of them. Typical but non-limiting combinations include a combination of nickel, cobalt and manganese or a combination of nickel and manganese, etc., 0.9≤x≤0.98, 0.02<y≤0.1.

[0013] Preferably, the median particle size D50 of the doped core is 5 μm to 10 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0014] Preferably, the chemical formula of the doped cladding layer includes N a Nb b (OH)2、N a Nb b CO3 or N a Nb b Any one or a combination of at least two of C2O4, N includes any one or a combination of at least two of nickel, cobalt or manganese, typical but non-limiting combinations include a combination of nickel, cobalt and manganese or a combination of nickel and manganese, etc., 0.9≤a≤0.98, 0.02<b≤0.1.

[0015] Preferably, the thickness of the doped cladding layer is 2 μm to 8 μm, for example, 2 μm, 3 μm, 5 μm, 6 μm or 8 μm, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0016] In a second aspect, the present invention provides a method for preparing the modified positive electrode precursor, the method comprising the following steps:

[0017] (1) spray pyrolysis treatment of a first precursor solution containing titanium to obtain titanium-doped oxide seed crystals with a hollow structure;

[0018] (2) The oxide seed crystals prepared in step (1) are placed in the bottom liquid as seed crystals, and the second precursor solution, niobium source solution, precipitant solution and complexing agent solution are injected into the bottom liquid in parallel to perform a co-precipitation reaction to obtain the modified positive electrode precursor.

[0019] During the preparation of the modified positive electrode precursor described in the present invention, titanium-doped oxide seed crystals are prepared by spray pyrolysis. The ionic radius of Ti ions differs significantly from that of transition metals such as Ni and Co ions. Conventional coprecipitation methods easily lead to uneven doping of the titanium element. Furthermore, titanium ions easily form colloidal TiO(OH)2 in an alkaline coprecipitation environment, which is easily hydrolyzed to form a TiO2 impurity phase during coprecipitation. However, the present invention uses the high-temperature instantaneous reaction of spray pyrolysis to force titanium ions into the crystal lattice, forming a uniform solid solution. Furthermore, spray pyrolysis can avoid localized excessive concentrations and the formation of TiO2 impurity phases through rapid drying and thermal decomposition. However, if niobium is doped by spray pyrolysis, niobium ions easily react with oxygen at high temperatures to form stable Nb2O5 particles, resulting in a decrease in doping efficiency. The ionic radius of niobium ions is similar to that of nickel ions. The present invention uses titanium-doped oxide seed crystals with a hollow interior as crystal nuclei to achieve uniform niobium atomic-level doping through coprecipitation. The present invention aims at the different properties of titanium and niobium, and arranges them in the core and the coating layer respectively by appropriate methods, which can significantly improve the capacity and cycle stability of the positive electrode precursor.

[0020] Preferably, the total molar concentration of metal ions in the titanium-containing first precursor solution in step (1) is 1 mol / L to 2 mol / L, for example: 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L or 2 mol / L, etc., and is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0021] Preferably, the temperature of the spray pyrolysis treatment in step (1) is 700°C to 800°C, for example, 700°C, 720°C, 750°C, 780°C or 800°C, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0022] Preferably, the time of the spray pyrolysis treatment in step (1) is 5 h to 10 h, for example, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0023] Preferably, the base liquid in step (2) contains a precipitant and a complexing agent.

[0024] Preferably, the total molar concentration of metal ions in the second precursor solution in step (2) is 1 mol / L to 2 mol / L, for example: 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L or 2 mol / L, etc., and is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0025] Preferably, the solute of the niobium source solution in step (2) includes niobium oxalate and / or niobium chloride.

[0026] Preferably, the molar concentration of the niobium source solution in step (2) is 0.01 mol / L to 0.1 mol / L, for example, 0.01 mol / L, 0.02 mol / L, 0.05 mol / L, 0.08 mol / L or 0.1 mol / L, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0027] Preferably, the solute of the precipitant solution in step (2) includes any one or a combination of at least two of liquid caustic soda, ammonia water, oxalate or carbonate. Typical but non-limiting combinations include a combination of liquid caustic soda and ammonia water, a combination of liquid caustic soda and oxalate, or a combination of oxalate and carbonate.

[0028] Preferably, the mass percentage concentration of the precipitant solution in step (2) is 20% to 40%, for example: 20%, 25%, 30%, 35% or 40%, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0029] Preferably, the solute of the complexing agent solution in step (2) includes any one or a combination of at least two of ammonia water, citrate or EDTA. Typical but non-limiting combinations include a combination of ammonia water and citrate, a combination of ammonia water and EDTA, or a combination of citrate and EDTA, and the citrate includes sodium citrate.

[0030] Preferably, the mass percentage concentration of the complexing agent solution in step (2) is 10% to 20%, for example: 10%, 12%, 15%, 18% or 20%, etc., not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the pH of the coprecipitation reaction in step (2) is 9 to 12, for example, 9, 10, 10.5, 11, 11.5 or 12, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0032] Preferably, the temperature of the coprecipitation reaction in step (2) is 40°C to 75°C, for example, 50°C, 52°C, 55°C, 58°C or 60°C, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0033] In a third aspect, the present invention provides a positive electrode material, which is obtained by mixing and sintering the modified positive electrode precursor as described in the first aspect with a lithium source and / or a sodium source.

[0034] Preferably, the lithium source comprises lithium hydroxide and / or lithium carbonate.

[0035] Preferably, the sodium source comprises sodium carbonate.

[0036] Preferably, the sintering temperature is 800°C to 1200°C, for example, 800°C, 900°C, 1000°C, 1100°C or 1200°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0037] In a fourth aspect, the present invention provides a secondary battery, comprising the positive electrode material as described in the third aspect.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The modified positive electrode precursor of the present invention has a structure of a titanium-doped hollow core and a niobium-doped coating layer. Uniform titanium doping can ensure the structural stability of the hollow core, provide a buffer space for lithium ion insertion / ejection during the charge and discharge process while ensuring structural stability, reduce the risk of particle breakage, shorten the lithium ion diffusion distance, and improve the rate performance; niobium is uniformly doped in the coating layer, and niobium ions form a Li-Nb-O spinel phase on the surface of the particles, which inhibits the decomposition of the electrolyte and the dissolution of transition metals while promoting the surface Li + Fast transmission, reduced interface impedance, the interaction between the titanium core and the niobium shell can form a built-in electric field, accelerating Li + transport across the interface while balancing the charge distribution.

[0040] (2) The structure of the positive electrode precursor of the present invention is suitable for preparing various ternary positive electrode materials. Among them, the 0.1C discharge capacity of the ternary lithium battery made of the positive electrode precursor with a nickel content of 65% can reach 186.6mAh / g, the 0.33C discharge capacity can reach 175.22mAh / g, the 1C discharge capacity can reach 150.47mAh / g, and the capacity retention rate after 50 cycles can reach 92.8%. The 0.1C discharge capacity of the ternary lithium battery made of the positive electrode precursor with a nickel content of 80% can reach 205.3 3mAh / g, the 0.33C discharge specific capacity can reach 199.14mAh / g, the 1C discharge specific capacity can reach 190.42mAh / g, and the capacity retention rate can reach 92% after 50 cycles. The 0.1C discharge specific capacity of the ternary lithium battery made of the positive electrode precursor with a nickel content of 90% can reach 220.05mAh / g, the 0.33C discharge specific capacity can reach 215.26mAh / g, the 1C discharge specific capacity can reach 208.75mAh / g, and the capacity retention rate can reach 90.4% after 50 cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is an SEM image of the modified positive electrode precursor prepared in Example 1 of the present invention.

[0042] Figure 2 This is a SEM cross-sectional view of the modified positive electrode precursor obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0044] Example 1

[0045] This embodiment provides a modified positive electrode precursor, which includes a titanium-doped nickel-cobalt-manganese oxide core with a hollow structure and a niobium-doped nickel-cobalt-manganese hydroxide coating layer disposed on the surface of the core. The chemical formula of the core is Ni 0.65 Mn 0.20 Co 0.1 Ti 0.05 O2, the chemical formula of the coating is Ni 0.65 Mn 0.2 Co 0.1 Nb 0.05 (OH)2.

[0046] The SEM image of the modified positive electrode precursor is as follows: Figure 1 As shown, the SEM cross-sectional view of the modified positive electrode precursor is as shown Figure 2 As shown by Figure 2It can be seen that the interior of the modified positive electrode precursor shown in this application is a hollow structure.

[0047] The modified positive electrode precursor is prepared by the following method:

[0048] (1) preparing a titanium-containing nickel-cobalt-manganese chloride solution, wherein the molar ratio of each metal in the solution is Ni:Mn:Co:Ti is 0.65:0.20:0.1:0.05; the total molar concentration of metal ions is 1.5 mol / L, and the titanium-containing nickel-cobalt-manganese chloride solution is spray-pyrolyzed at 750° C. for 8 h to obtain titanium-doped oxide seeds with a hollow structure inside, wherein the median particle size D50 of the oxide seeds is 6 μm;

[0049] (2) preparing a base liquid containing sodium hydroxide and ammonia water, placing the oxide seed crystals obtained in step (1) in the base liquid as seed crystals, and injecting a nickel-cobalt-manganese sulfate solution with a total molar concentration of nickel, cobalt and manganese of 1.5 mol / L, a niobium chloride solution with a molar concentration of 0.05 mol / L, a sodium hydroxide solution with a mass percentage concentration of 30%, and ammonia water with a mass percentage concentration of 15% into the base liquid in parallel, and performing a coprecipitation reaction under the conditions of 55° C. and pH = 10.5 to obtain the modified positive electrode precursor, wherein the median particle size D50 of the modified positive electrode precursor is 15 μm and the thickness of the coating layer is 4.5 μm.

[0050] Example 2

[0051] This embodiment provides a modified positive electrode precursor, which includes a titanium-doped nickel-cobalt-manganese oxide core with a hollow structure and a niobium-doped nickel-cobalt-manganese hydroxide coating layer disposed on the surface of the core. The chemical formula of the core is Ni 0.8 Mn 0.1 Co 0.05 Ti 0.05 O2, the chemical formula of the coating is Ni 0.8 Mn 0.1 Co 0.05 Nb 0.05 (OH)2.

[0052] The modified positive electrode precursor is prepared by the following method:

[0053] (1) preparing a titanium-containing nickel-cobalt-manganese chloride solution, wherein the molar ratio of each metal in the solution is Ni:Mn:Co:Ti is 0.8:0.10:0.05:0.05; the total metal ion concentration is 2 mol / L, and the titanium-containing nickel-cobalt-manganese sulfate solution is spray-pyrolyzed at 700° C. for 10 h to obtain titanium-doped oxide seeds with a hollow structure inside, wherein the median particle size D50 of the oxide seeds is 5 μm;

[0054] (2) preparing a base liquid containing sodium hydroxide and ammonia water, placing the oxide seed crystals prepared in step (1) in the base liquid as seed crystals, and injecting a nickel-cobalt-manganese sulfate solution with a total molar concentration of nickel-cobalt-manganese of 1 mol / L, a niobium chloride solution with a molar concentration of 0.1 mol / L, a sodium hydroxide solution with a mass percentage concentration of 20%, and ammonia water with a mass percentage concentration of 10% into the base liquid in parallel, and performing a coprecipitation reaction under the conditions of 65° C. and pH = 10.5 to obtain the modified positive electrode precursor, wherein the median particle size D50 of the modified positive electrode precursor is 9 μm and the thickness of the coating layer is 2 μm.

[0055] Example 3

[0056] This embodiment provides a modified positive electrode precursor, which includes a titanium-doped nickel-cobalt-manganese oxide core with a hollow structure and a niobium-doped nickel-cobalt-manganese hydroxide coating layer disposed on the surface of the core. The chemical formula of the core is Ni 0.9 Mn 0.05 Co 0.03 Ti 0.02 O2, the chemical formula of the coating is Ni 0.9 Mn 0.05 Co 0.03 Nb 0.02 (OH)2.

[0057] The modified positive electrode precursor is prepared by the following method:

[0058] (1) preparing a titanium-containing nickel-cobalt-manganese sulfate solution, wherein the molar ratio of each metal in the solution is Ni:Mn:Co:Ti is 0.90:0.05:0.03:0.02; the total metal ion concentration is 2 mol / L, and the titanium-containing nickel-cobalt-manganese sulfate solution is subjected to spray pyrolysis treatment at 800° C. for 5 h to obtain titanium-doped oxide seeds with a hollow structure inside, wherein the median particle size D50 of the oxide seeds is 10 μm;

[0059] (2) preparing a base liquid containing sodium hydroxide and ammonia water, placing the oxide seed crystals obtained in step (1) in the base liquid as seed crystals, and injecting a nickel-cobalt-manganese sulfate solution with a total molar concentration of nickel-cobalt-manganese of 2 mol / L, a niobium chloride solution with a molar concentration of 0.01 mol / L, a sodium hydroxide solution with a mass percentage concentration of 40%, and ammonia water with a mass percentage concentration of 20% into the base liquid in parallel, and performing a coprecipitation reaction at 65° C. and pH = 10 to obtain the modified positive electrode precursor, wherein the median particle size D50 of the modified positive electrode precursor is 26 μm and the thickness of the coating layer is 8 μm.

[0060] Example 4

[0061] The only difference between this embodiment and embodiment 1 is that the molar ratio of titanium in the core metal element is 0.01 mol %, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0062] Example 5

[0063] The only difference between this embodiment and embodiment 1 is that the molar ratio of titanium in the core metal element is 0.2 mol %. Other conditions and parameters are exactly the same as those in embodiment 1.

[0064] Example 6

[0065] The only difference between this embodiment and embodiment 1 is that the molar proportion of niobium in the metal elements of the coating layer is 0.01 mol %. Other conditions and parameters are exactly the same as those in embodiment 1.

[0066] Example 7

[0067] The only difference between this embodiment and embodiment 1 is that the molar ratio of niobium in the metal elements of the coating layer is 0.2 mol %. Other conditions and parameters are exactly the same as those in embodiment 1.

[0068] Example 8

[0069] The only difference between this embodiment and embodiment 1 is that the temperature of the spray pyrolysis is 600° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0070] Example 9

[0071] The only difference between this embodiment and embodiment 1 is that the temperature of the spray pyrolysis is 900° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0072] Comparative Example 1

[0073] The only difference between this comparative example and Example 1 is that the core is not doped with titanium, and the other conditions and parameters are exactly the same as those in Example 1.

[0074] Comparative Example 2

[0075] The only difference between this comparative example and Example 1 is that the coating layer is not doped with niobium, and the other conditions and parameters are exactly the same as those in Example 1.

[0076] Comparative Example 3

[0077] The only difference between this comparative example and Example 1 is that the core seed crystals are prepared by a co-precipitation method, and the other conditions and parameters are exactly the same as those in Example 1.

[0078] Performance testing:

[0079] The positive electrode precursors prepared in the examples and comparative examples were mixed with lithium hydroxide in a molar ratio of Li:Ni+Co+Mn=1.05:1 and sintered at 900°C for 10h to obtain the positive electrode material. The positive electrode material was mixed with polyvinylidene fluoride, acetylene black and N-methylpyrrolidone in a mass ratio of 96:2:2, wherein the mass ratio of solid to liquid was 7:3, to prepare the positive electrode slurry. After coating the cut pieces, it was vacuum dried at 120°C for 12h and transferred to the glove box. The metal lithium sheet was used as the negative electrode and the battery shell was CR2032 to make a button battery. At 25°C, the discharge specific capacity at 0.1C, 0.33C and 1C and the capacity retention rate after 50 cycles were tested respectively. The test results are shown in Table 1:

[0080] Table 1

[0081]

[0082] As can be seen from Table 1, it can be obtained from Examples 1-3 that the positive electrode precursor prepared by the present invention can be used to prepare various ternary positive electrode materials, among which the 0.1C discharge capacity of the ternary lithium battery made from the positive electrode precursor with a nickel content of 65% can reach 186.6mAh / g, the 0.33C discharge capacity can reach 175.22mAh / g, the 1C discharge capacity can reach 150.47mAh / g, and the capacity retention rate after 50 cycles can reach 92.8%. The 0.1C discharge capacity of the ternary lithium battery made from the positive electrode precursor with a nickel content of 80% can reach 100. The capacity can reach 205.33mAh / g, the 0.33C discharge specific capacity can reach 199.14mAh / g, the 1C discharge specific capacity can reach 190.42mAh / g, and the capacity retention rate after 50 cycles can reach 92%. The 0.1C discharge specific capacity of the ternary lithium battery made of the positive electrode precursor with a nickel content of 90% can reach 220.05mAh / g, the 0.33C discharge specific capacity can reach 215.26mAh / g, the 1C discharge specific capacity can reach 208.75mAh / g, and the capacity retention rate after 50 cycles can reach 90.4%.

[0083] By comparing Example 1 with Examples 4-5, it can be seen that the amount of titanium doping in the core of the modified positive electrode precursor of the present invention affects its performance. The molar proportion of titanium in the core metal element is controlled between 0.02 mol% and 0.1 mol%. The performance of the modified positive electrode precursor is better. If the titanium doping amount in the core is too low, the effect is not obvious; if the titanium doping amount in the core is too high, it occupies too many nickel, cobalt and manganese atomic positions, affecting the capacity.

[0084] By comparing Example 1 with Examples 6-7, it can be seen that the niobium doping amount in the coating layer of the modified positive electrode precursor of the present invention affects its performance. When the molar ratio of niobium in the metal element of the coating layer is controlled between 0.02 mol% and 0.1 mol%, the performance of the modified positive electrode precursor is better. If the niobium doping amount in the coating layer is too low, the effect is not obvious. If the niobium doping amount in the coating layer is too high, it also replaces the position of nickel, cobalt and manganese, affecting the capacity.

[0085] By comparing Example 1 with Examples 8-9, it can be seen that during the preparation process of the modified positive electrode precursor of the present invention, the temperature of the spray pyrolysis will affect its performance. When the temperature of the spray pyrolysis is controlled at 700°C to 800°C, the performance of the modified positive electrode precursor is better. If the temperature of the spray pyrolysis is too low, the capacity becomes lower. This is mainly because the spray pyrolysis temperature is low and the core contains too many undecomposed anions, such as impurity components composed of anions such as Cl, S, and N, which are difficult to remove. If the temperature of the spray pyrolysis is too high, the core is overoxidized and the crystal structure changes, resulting in a lower capacity.

[0086] By comparing Example 1 and Comparative Example 1, it can be seen that the present invention can uniformly dope titanium in the core of the modified positive electrode precursor, and the titanium element can preferentially occupy the transition metal site, stabilize the lattice structure, and inhibit the phase change during the cycle. The strong Ti-O bond energy of the titanium ion can enhance the stability of the inner core oxygen framework and reduce oxygen loss under high voltage.

[0087] From the comparison between Example 1 and Comparative Example 2, it can be seen that doping niobium into the coating layer of the modified positive electrode precursor in the present invention can significantly improve the stability of the coating layer and passivate the side reactions at the interface.

[0088] From the comparison between Example 1 and Comparative Example 3, it can be seen that the present invention uses a spray pyrolysis method to prepare an internal hollow oxide as a seed to prepare a positive electrode precursor. The hollow core structure provides a buffer space for lithium ion insertion / ejection during the charge and discharge process, reducing the risk of particle breakage. The thin-walled hollow structure of the core can shorten the Li + The diffusion distance is shortened to improve the rate performance.

[0089] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A modified cathode precursor, characterized in that: The modified positive electrode precursor includes a doped core and a doped coating layer disposed on the surface of the doped core; The interior of the doped core is a hollow structure; The doped core contains titanium element, and the doped cladding layer contains niobium element.

2. The modified positive electrode precursor according to claim 1, characterized in that The chemical formula of the doped core includes M x Ti y O2, M includes any one of nickel, cobalt or manganese or a combination of at least two thereof, 0.9≤x≤0.98, 0.02<y≤0.1; Preferably, the median particle size D50 of the doped core is 5 μm to 10 μm.

3. The modified positive electrode precursor according to claim 1 or 2, characterized in that The chemical formula of the doped cladding layer includes N a Nb b (OH)2、N a Nb b CO3 or N a Nb b Any one or a combination of at least two of C2O4, N includes any one or a combination of at least two of nickel, cobalt or manganese, 0.9≤a≤0.98, 0.02<b≤0.1; Preferably, the thickness of the doped cladding layer is 2 μm to 8 μm; Preferably, the median particle size D50 of the modified positive electrode precursor is 9 μm to 26 μm.

4. A method for preparing a modified positive electrode precursor according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: (1) spray pyrolysis treatment of a first precursor solution containing titanium to obtain titanium-doped oxide seed crystals with a hollow structure; (2) The oxide seed crystals prepared in step (1) are placed in the bottom liquid as seed crystals, and the second precursor solution, niobium source solution, precipitant solution and complexing agent solution are injected into the bottom liquid in parallel to perform a co-precipitation reaction to obtain the modified positive electrode precursor.

5. The preparation method according to claim 4, wherein The total molar concentration of metal ions in the first titanium-containing precursor solution in step (1) is 1 mol / L to 2 mol / L.

6. The preparation method according to claim 4 or 5, characterized in that The temperature of the spray pyrolysis treatment in step (1) is 700° C. to 800° C.; Preferably, the spray pyrolysis treatment time in step (1) is 5 h to 10 h.

7. The preparation method according to any one of claims 4 to 6, characterized in that The base liquid in step (2) contains a precipitant and a complexing agent; Preferably, the total molar concentration of metal ions in the second precursor solution in step (2) is 1 mol / L to 2 mol / L; Preferably, the solute of the niobium source solution in step (2) includes niobium oxalate and / or niobium chloride; Preferably, the molar concentration of the niobium source solution in step (2) is 0.01 mol / L to 0.1 mol / L; Preferably, the solute of the precipitant solution in step (2) includes any one or a combination of at least two of liquid alkali, ammonia, oxalate or carbonate; Preferably, the mass percentage concentration of the precipitant solution in step (2) is 20% to 40%; Preferably, the solute of the complexing agent solution in step (2) includes any one of ammonia, citrate or EDTA, or a combination of at least two thereof; Preferably, the mass percentage concentration of the complexing agent solution in step (2) is 10% to 20%.

8. The preparation method according to any one of claims 4 to 7, wherein: The pH of the coprecipitation reaction in step (2) is 10-12; Preferably, the temperature of the coprecipitation reaction in step (2) is 50°C to 60°C.

9. A positive electrode material, characterized in that The positive electrode material is obtained by mixing and sintering the modified positive electrode precursor according to any one of claims 1 to 3 with a lithium source and / or a sodium source.

10. A secondary battery, characterized in that: The secondary battery includes the positive electrode material according to claim 9.

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