Composite positive electrode material and preparation method thereof, positive plate and lithium ion battery

Abstract

The invention provides a composite positive electrode material and a preparation method thereof, a positive plate and a lithium ion battery. The composite positive electrode material comprises a lithium-rich manganese-based positive electrode material and a perovskite type oxide coated on the surface of the lithium-rich manganese-based positive electrode material, the chemical formula of the perovskite type oxide is Li2x-ySr1-xZr1-yNbyO3, x is equal to 3y / 4, and y is equal to 0.5-0.7. The perovskite type oxide has relatively high ionic conductivity, a relatively wide electrochemical platform and a stable structure, and is coated on the surface of the lithium-rich manganese-based positive electrode material, so that on one hand, the contact between the lithium-rich manganese-based positive electrode material and an electrolyte is reduced, the generation of side reactions is reduced, and the service life of the lithium-rich manganese-based positive electrode material is prolonged; and on the other hand, the first coulombic efficiency can be improved. And the conductivity of the lithium-rich manganese-based positive electrode material can be improved, the lithium ion transfer impedance of a liquid phase and a solid phase can be reduced, and the rate capability can be enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a composite positive electrode material and a preparation method thereof, a positive electrode sheet and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries are widely used due to their high discharge capacity, long cycle life, and portability. Current lithium-ion battery development is focused on increasing both volume and energy density. Furthermore, the development of cathode materials for lithium-ion batteries requires improving their cycling performance, increasing safety, and reducing production costs.

[0003] Lithium-rich manganese-based cathode materials have ultra-high discharge capacity (>250mAh·g -1 ) and a high operating voltage (2.0-4.8V), further improving the energy density of lithium-ion batteries. It also reduces the toxic Co content and increases the less expensive Mn content, lowering material production costs while improving environmental performance. However, lithium-rich manganese-based cathode materials suffer from low first-cycle coulombic efficiency and poor cycling performance. Summary of the Invention

[0004] The main purpose of the present invention is to provide a composite positive electrode material and its preparation method, a positive electrode sheet and a lithium ion battery, so as to solve the problems of low first-cycle coulombic efficiency and poor cycle performance of lithium-rich manganese-based positive electrode materials in the prior art.

[0005] In order to achieve the above object, according to one aspect of the present invention, a composite positive electrode material is provided, which comprises a lithium-rich manganese-based positive electrode material and a perovskite-type oxide coated on the surface of the lithium-rich manganese-based positive electrode material, wherein the chemical formula of the perovskite-type oxide is Li 2x-y Sr 1-x Zr 1-y Nb y O3, where x=3y / 4, y=0.5~0.7.

[0006] Furthermore, the mass ratio of the lithium-rich manganese-based cathode material to the perovskite-type oxide is 1:(0.01-0.03); preferably, the chemical formula of the lithium-rich manganese-based cathode material is Li[Li 1-a-b-c Mn a Co b Ni c ]O2, where a+b+c=0.8, a=0.50~0.60, b=0.10~0.15, c=0.10~0.15.

[0007] Furthermore, the ionic conductivity of the perovskite oxide is 2.04×10 -5 ~3.62×10-5 S / cm.

[0008] According to another aspect of the present invention, a method for preparing the aforementioned composite positive electrode material is provided, the preparation method comprising: step S1, mixing raw materials including a lithium-rich manganese-based positive electrode material, a strontium source, a zirconium source, a niobium source and water to obtain a precursor; step S2, calcining the precursor to obtain a composite positive electrode material.

[0009] Furthermore, the temperature of the mixing treatment is 50-80° C.; and / or the time of the mixing treatment is 3-6 hours.

[0010] Furthermore, the mixing process is performed under stirring, and the stirring speed of the mixing process is 100 to 350 rpm.

[0011] Furthermore, the heating rate of the calcination treatment is 2-10° C. / min; and / or the temperature of the calcination treatment is 600-1000° C.; and / or the holding time of the calcination treatment is 8-20 h.

[0012] Furthermore, the pH value of the solution in the above mixing treatment is 6.5-7.5; and / or the strontium source is selected from any one or more of strontium nitrate, strontium oxalate and strontium acetate; and / or the zirconium source is selected from any one or more of zirconium oxynitrate, zirconium nitrate and zirconium oxide; and / or the niobium source is niobium pentoxide and / or ammonium niobium oxalate.

[0013] According to another aspect of the present invention, a positive electrode sheet is provided, comprising a current collector and a positive electrode active layer, wherein the positive electrode active layer contains the aforementioned composite positive electrode material.

[0014] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode sheet, an electrolyte, and a negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet described above.

[0015] By applying the technical solution of the present invention, the perovskite oxide of the present invention has high ionic conductivity, a wide electrochemical platform and a stable structure. Coating it on the surface of the lithium-rich manganese-based positive electrode material can help reduce the contact between the lithium-rich manganese-based positive electrode material and the electrolyte, thereby helping to reduce the generation of side reactions, and on the other hand, help to improve the first coulombic efficiency. And Li 2x-y Sr 1-x Zr 1-y Nb y As a lithium ion conductor with low grain boundary resistance, O3 can play a positive role in improving lithium diffusion efficiency, helping to improve the conductivity of lithium-rich manganese-based positive electrode materials, reduce the lithium ion transfer impedance between liquid and solid phases, and enhance rate performance. 2x-y Sr 1-x Zr 1-y Nby The O3 coating layer interface is a cubic perovskite structure with nano-scale defects and a large number of A-site defects. As the cycle progresses, the loss of Li and the dissolution of transition metals will cause oxygen vacancies in the coating layer. Due to the anionic redox mechanism of the lithium-rich manganese-based cathode material, oxygen will be released during the cycle, causing the structure of the cathode material itself to decay, resulting in rapid capacity decay during the cycle. 2x-y Sr 1- x Zr 1-y Nb y The presence of the O3 coating layer can fix the incompletely released oxygen in the oxygen vacancies of the coating layer, inhibit the release of oxygen, and slow down the capacity decay and structural degradation of the lithium-rich manganese-based cathode material during cycling. 2x-y Sr 1-x Zr 1-y Nb y Too large or too small y in O3 is not conducive to improving the ionic conductivity of the composite positive electrode material. Controlling the value of y within the range of 0.5 to 0.7 helps to further improve the ionic conductivity of the composite positive electrode material and improve the structural stability of the composite positive electrode material, thereby helping to further improve the first-cycle coulombic efficiency and cycle stability of the composite positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0017] Figure 1 Shown are XRD comparison diagrams of the positive electrode materials of Example 1 and Comparative Example 1 of the present application;

[0018] Figure 2 The figure shows the lithium ion diffusion performance of the positive electrode materials of Example 1 and Comparative Example 1 of the present application during the charging process;

[0019] Figure 3 The graph shows the lithium ion diffusion performance of the positive electrode materials of Example 1 and Comparative Example 1 of the present application during the discharge process. DETAILED DESCRIPTION

[0020] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0021] As analyzed in the background technology of this application, the lithium-rich manganese-based positive electrode materials in the prior art have the problems of low first-cycle coulombic efficiency and poor cycle performance. In order to solve the above problems, this application provides a composite positive electrode material and its preparation method, a positive electrode sheet and a lithium-ion battery.

[0022] In a typical embodiment of the present application, a composite positive electrode material is provided, which includes a lithium-rich manganese-based positive electrode material and a perovskite-type oxide coated on the surface of the lithium-rich manganese-based positive electrode material. The chemical formula of the perovskite-type oxide is Li 2x-y Sr 1-x Zr 1-y Nb y O3, where x=3y / 4, y=0.5~0.7.

[0023] The perovskite oxide of the present application has high ionic conductivity, a wide electrochemical platform and a stable structure. Coating it on the surface of the lithium-rich manganese-based positive electrode material can help reduce the contact between the lithium-rich manganese-based positive electrode material and the electrolyte, thereby helping to reduce the generation of side reactions, and on the other hand, help to improve the first coulombic efficiency. And Li 2x- y Sr 1-x Zr 1-y Nb y As a lithium ion conductor with low grain boundary resistance, O3 can play a positive role in improving lithium diffusion efficiency, helping to improve the conductivity of lithium-rich manganese-based positive electrode materials, reduce the lithium ion transfer impedance between liquid and solid phases, and enhance rate performance. 2x-y Sr 1-x Zr 1-y Nb y The O3 coating layer interface is a cubic perovskite structure with nano-scale defects and a large number of A-site defects. As the cycle progresses, the loss of Li and the dissolution of transition metals will cause oxygen vacancies in the coating layer. Due to the anionic redox mechanism of the lithium-rich manganese-based cathode material, oxygen will be released during the cycle, causing the structure of the cathode material itself to decay, resulting in rapid capacity decay during the cycle. 2x-y Sr 1-x Zr 1-y Nb y The presence of the O3 coating layer can fix the incompletely released oxygen in the oxygen vacancies of the coating layer, inhibit the release of oxygen, and slow down the capacity decay and structural degradation of the lithium-rich manganese-based cathode material during cycling. 2x-y Sr 1-x Zr 1-y Nb yToo large or too small y in O3 is not conducive to improving the ionic conductivity of the composite positive electrode material. Controlling the value of y within the range of 0.5 to 0.7 helps to further improve the ionic conductivity of the composite positive electrode material and improve the structural stability of the composite positive electrode material, thereby helping to further improve the first-cycle coulombic efficiency and cycle stability of the composite positive electrode material.

[0024] Preferably, y=0.5, 0.6 or 0.7, which helps to form a more stable cubic perovskite structure, thereby helping to further improve the first-cycle coulombic efficiency and cycle stability of the composite positive electrode material.

[0025] In one embodiment of the present application, the mass ratio of the above-mentioned lithium-rich manganese-based positive electrode material to the perovskite-type oxide is 1:(0.01-0.03), specifically 1:0.01, 1:0.015, 1:0.02, 1:0.025, 1:0.03 and a range value between any two values; preferably, the chemical formula of the lithium-rich manganese-based positive electrode material is Li[Li 1-a-b-c Mn a Co b Ni c ]O2, wherein a=0.50~0.60, b=0.10~0.15, c=0.10~0.15, further preferably, a can be specifically 0.50, 0.52, 0.53, 0.54, 0.55, 0.60 and a range value between any two values, b can be specifically 0.10, 0.12, 0.13, 0.14, 0.15 and a range value between any two values, c can be specifically 0.10, 0.12, 0.13, 0.14, 0.15 and a range value between any two values, most preferably, the chemical formula of the lithium-rich manganese-based positive electrode material is Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2.

[0026] Controlling the mass ratio of lithium-rich manganese-based cathode materials to perovskite-type oxides within the above range helps improve the electrochemical stability of the cathode materials, reduces direct contact between the lithium-rich manganese-based cathode materials and the electrolyte, reduces side reactions, and helps stabilize the crystal structure of the cathode materials, thereby helping to improve the cycle performance and first coulombic efficiency of the cathode materials. 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2 has higher capacity and lower cost, and is suitable for Li 1.2 Mn 0.54 Co 0.13 Ni 0.13Perovskite-type oxides are formed in situ on the surface of O2, which helps to improve the first-cycle coulombic efficiency and cycle stability of the composite positive electrode material.

[0027] In order to further improve the first cycle coulombic efficiency of the composite positive electrode material, in one embodiment of the present application, the ionic conductivity of the perovskite oxide is preferably 2.04×10 -5 ~3.62×10 -5 S / cm; and / or, the lithium ion diffusion coefficient of the composite positive electrode material during charging is 10 -12.51 ~10 -13.14 cm 2 / s; and / or, the lithium ion diffusion coefficient of the composite positive electrode material during discharge is 10 -11.26 ~10 -12.16 cm 2 / s.

[0028] In another typical embodiment of the present application, a method for preparing the aforementioned composite positive electrode material is provided, which comprises: step S1, mixing raw materials including a lithium-rich manganese-based positive electrode material, a strontium source, a zirconium source, a niobium source and water to obtain a precursor; step S2, calcining the precursor to obtain a composite positive electrode material.

[0029] In step S1, a lithium-rich manganese-based positive electrode material, a strontium source, a zirconium source, a niobium source and water are mixed, which helps to uniformly adhere the strontium source, the zirconium source and the niobium source to the surface of the lithium-rich manganese-based positive electrode material to form a precursor; in step S2, the precursor is calcined, which helps to form a perovskite-type oxide coating layer in situ on the surface of the lithium-rich manganese-based positive electrode material. The perovskite-type oxide has high ionic conductivity, and its electrochemical platform is wide and the structure is stable. It is coated on the surface of the lithium-rich manganese-based positive electrode material, which helps to reduce the contact between the lithium-rich manganese-based positive electrode material and the electrolyte, thereby helping to reduce the generation of side reactions, and on the other hand helps to improve the first coulombic efficiency. The lithium source in the perovskite-type oxide coating layer in this application comes from the lithium-rich manganese-based positive electrode material.

[0030] In one embodiment of the present application, the temperature of the above-mentioned mixing treatment is 50-80°C, specifically 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C and a range value between any two values; and / or, the mixing treatment time is 3-6h.

[0031] Controlling the temperature and time of the mixing treatment within the above range, on the one hand, helps to improve the interaction between the strontium source, zirconium source, niobium source and the surface of the lithium-rich manganese-based positive electrode material, and on the other hand, helps to improve the dispersion uniformity of the strontium source, zirconium source, and niobium source on the surface of the lithium-rich manganese-based positive electrode material, thereby helping to form a perovskite-type oxide layer with better thickness uniformity.

[0032] In order to further improve the distribution uniformity of the strontium source, zirconium source and niobium source on the surface of the lithium-rich manganese-based positive electrode material, in one embodiment of the present application, the above-mentioned mixing treatment is preferably carried out under stirring, and the stirring speed of the mixing treatment is 100 to 350 rpm.

[0033] In one embodiment of the present application, the heating rate of the calcination treatment is 2 to 10°C / min; and / or the calcination temperature is 600 to 1000°C, preferably 800 to 1000°C, specifically 800°C, 900°C, 1000°C and a range between any two values; and / or the holding time of the calcination treatment is 8 to 20h.

[0034] Controlling the calcination temperature rate within the above range helps improve the uniformity of the material's heating during the calcination process, reducing structural unevenness or coating defects caused by localized overheating. It also promotes uniform stress release within the material, reducing crack formation, and thereby improving the uniformity and density of the coating. Higher calcination temperatures promote metal ion diffusion and oxide formation, increasing the crystallinity of the coating and making it more stable, thereby enhancing the cycling stability and structural integrity of the cathode material. However, excessively high temperatures may also lead to over-sintering of the material, destroying the original particle size and morphology, and affecting lithium ion diffusion efficiency. Controlling the calcination temperature within the above range helps further improve the first-cycle coulombic efficiency and cycling stability of the composite cathode material. Too short a holding time may prevent a full reaction from occurring, resulting in an incomplete coating or low crystallinity. Excessive holding times increase energy consumption and may cause structural changes or over-sintering of the coating, ultimately reducing material performance. Controlling the holding time within the above range helps form a structurally stable, high-performance perovskite oxide coating.

[0035] In one embodiment of the present application, the pH value of the solution in the above-mentioned mixing treatment is 6.5-7.5, preferably 7; and / or the strontium source is selected from any one or more of strontium nitrate, strontium oxalate and strontium acetate; and / or the zirconium source is selected from any one or more of zirconium oxynitrate, zirconium nitrate and zirconium oxide; and / or the niobium source is niobium pentoxide and / or ammonium niobium oxalate.

[0036] Controlling the pH of the solution during the mixing process within the aforementioned range helps promote the stable formation of the perovskite oxide precursor. Controlling the types of strontium, zirconium, and niobium sources within the aforementioned range helps enhance their interaction with the lithium in the lithium-rich manganese-based cathode material, thereby promoting the formation of the perovskite oxide precursor.

[0037] In one embodiment of the present application, the preparation method of the above-mentioned lithium-rich manganese-based positive electrode material includes: (1) dissolving a nickel source, a cobalt source, and a manganese source in deionized water and stirring uniformly; preparing 50 mL of a 1 mol / L KOH solution, adding 10 mL of a mixed solution of ammonia base and ammonia water, and mixing and stirring uniformly; (2) in a water bath at 55-65°C, introducing nitrogen gas, and dripping the above-mentioned two mixed solutions to make the pH of the mixed solution 12; (3) washing the obtained precipitate with 1.5 L of deionized water, drying it in a vacuum oven at 80°C for 24 hours, grinding it uniformly, mixing it with lithium hydroxide monohydrate, heating it to 800-1000°C at 5°C / min in a muffle furnace, keeping it warm for 12 hours, and then air-cooling and quenching it to obtain a lithium-rich manganese-based positive electrode material. Including but not limited to, the above-mentioned nickel source is nickel sulfate hexahydrate, the cobalt source is cobalt sulfate heptahydrate, the manganese source is manganese sulfate tetrahydrate, and the lithium source is lithium hydroxide monohydrate.

[0038] In another typical embodiment of the present application, a positive electrode sheet is provided, comprising a current collector and a positive electrode active layer, wherein the positive electrode active layer contains the aforementioned composite positive electrode material.

[0039] Since the above-mentioned positive electrode sheet contains the composite positive electrode material of the present application, the positive electrode sheet has a high first-cycle coulombic efficiency and cycle stability.

[0040] In another typical embodiment of the present application, a lithium-ion battery is provided, comprising a positive electrode sheet, an electrolyte, and a negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet described above.

[0041] Since the positive electrode sheet in the above-mentioned lithium-ion battery contains the composite positive electrode material of the present application, the lithium-ion battery has excellent first-cycle coulombic efficiency and cycle stability.

[0042] The beneficial effects of the present application will be further illustrated below with reference to examples.

[0043] Example 1

[0044] Preparation of lithium-rich manganese-based cathode materials Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2:

[0045] (1) Dissolve 4.44 g of nickel sulfate hexahydrate, 4.74 g of cobalt sulfate heptahydrate, and 15.69 g of manganese sulfate tetrahydrate in 100 mL of deionized water and stir evenly; prepare 50 mL of 1 mol / L KOH solution, add 10 mL of a mixed solution of ammonia base and ammonia water, and mix and stir evenly;

[0046] (2) In a 55°C water bath, nitrogen was introduced and the above two mixed solutions were added dropwise to make the pH of the mixed solution 12;

[0047] (3) The obtained precipitate was washed with 1.5 L of deionized water, dried in a vacuum oven at 80 ° C for 24 h, ground evenly, and mixed with 6.22 g of lithium hydroxide monohydrate. The temperature was raised to 900 ° C in a muffle furnace at 5 ° C / min, kept at this temperature for 12 hours, and then air-cooled to obtain Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2.

[0048] Preparation of composite cathode materials:

[0049] (1) 10g of the lithium-rich manganese-based cathode material Li prepared above 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2 is dissolved in deionized water to form solution A;

[0050] (2) dissolving 67.3 mg of strontium nitrate and 59 mg of zirconium oxynitrate in 10 mL of deionized water to obtain a first solution, dissolving 33.9 mg of niobium pentoxide in an oxalic acid solution to obtain a second solution, and mixing the first solution and the second solution to obtain a transition metal solution;

[0051] (3) The transition metal solution was added dropwise to solution A, the pH of the solution was adjusted to 7, and the mixture was stirred at 70°C for 3 h at a stirring speed of 200 rpm;

[0052] (4) After the stirred solution is completely dried, it is ground evenly and placed in a muffle furnace to obtain the final product. The temperature is raised to 800°C at 5°C / min, calcined for 12 hours, and then naturally cooled and ground to obtain the lithium-rich manganese-based positive electrode material Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 The surface of O2 is coated with a composite cathode material of perovskite-type oxide, the chemical formula of which is Li 0.25 Sr 0.625 Zr 0.5 Nb 0.5 O3, the ionic conductivity of perovskite oxide is 3.22×10 -5 S / cm, the mass ratio of lithium-rich manganese-based cathode material to perovskite-type oxide is 1:0.01, and the lithium ion diffusion coefficient of the composite cathode material during charging is 10 -12.82 cm 2 / s, the lithium ion diffusion coefficient of the composite cathode material during discharge is 10 -11.56 cm 2 / s.

[0053] Example 2

[0054] The difference from Example 1 is that the preparation of the composite positive electrode material includes the following steps:

[0055] (1) 10g of the lithium-rich manganese-based cathode material Li prepared above 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2 is dissolved in deionized water to form solution A;

[0056] (2) dissolving 67 mg of strontium nitrate and 53 mg of zirconium oxynitrate in 10 mL of deionized water to obtain a first solution, dissolving 46 mg of niobium pentoxide in an oxalic acid solution to obtain a second solution, and mixing the first solution and the second solution to obtain a transition metal solution;

[0057] (3) The transition metal solution was added dropwise to solution A, the pH of the solution was adjusted to 7, and the mixture was stirred at 70°C for 3 h at a stirring speed of 200 rpm;

[0058] (4) After the stirred solution is completely dried, it is ground evenly and placed in a muffle furnace to obtain the final product. The temperature is raised to 800°C at 5°C / min, kept at this temperature for 12 hours, and ground after natural cooling. The lithium-rich manganese-based positive electrode material Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 The surface of O2 is coated with a composite cathode material of perovskite-type oxide, the chemical formula of which is Li 0.3 Sr 0.55 Zr 0.4 Nb 0.6 O3, the ionic conductivity of perovskite oxide is 3.62×10 -5 S / cm, the mass ratio of lithium-rich manganese-based cathode material to perovskite-type oxide is 1:0.01, and the lithium ion diffusion coefficient of the composite cathode material during charging is 10 -12.91 cm 2 / s, the lithium ion diffusion coefficient of the composite cathode material during discharge is 10 -11.86 cm 2 / s.

[0059] Example 3

[0060] The difference from Example 1 is that the preparation of the composite positive electrode material includes the following steps:

[0061] (1) 10g of the lithium-rich manganese-based cathode material Li prepared above 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2 is dissolved in deionized water to form solution A;

[0062] (2) dissolving 54.5 mg of strontium nitrate and 37.6 mg of zirconium oxynitrate in 10 mL of deionized water to obtain a first solution, dissolving 50.4 mg of niobium pentoxide in a potassium hydroxide solution to obtain a second solution, and mixing the first solution and the second solution to obtain a transition metal solution;

[0063] (3) The transition metal solution was added dropwise to solution A, the pH of the solution was adjusted to 7, and the mixture was stirred at 70°C for 3 h at a stirring speed of 200 rpm;

[0064] (4) After the stirred solution is completely dried, it is ground evenly and placed in a muffle furnace to obtain the final product. The temperature is raised to 800°C at 5°C / min, kept at this temperature for 12 hours, and ground after natural cooling to obtain the lithium-rich manganese-based positive electrode material Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 The surface of O2 is coated with a composite cathode material of perovskite-type oxide, the chemical formula of which is Li 0.35 Sr 0.475 Zr 0.3 Nb 0.7 O3, the ionic conductivity of perovskite oxide is 2.04×10 -5 S / cm, the mass ratio of lithium-rich manganese-based cathode material to perovskite-type oxide is 1:0.01, and the lithium ion diffusion coefficient of the composite cathode material during charging is 10 -12.51 cm 2 / s, the lithium ion diffusion coefficient of the composite cathode material during discharge is 10 -11.26 cm 2 / s.

[0065] Example 4

[0066] The difference from Example 1 is that the preparation of the composite positive electrode material includes the following steps:

[0067] (1) 10g of the lithium-rich manganese-based cathode material Li prepared above 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2 is dissolved in deionized water to form solution A;

[0068] (2) dissolving 134.6 mg of strontium nitrate and 118 mg of zirconium oxynitrate in 10 mL of deionized water to obtain a first solution, dissolving 67.8 mg of niobium pentoxide in an oxalic acid solution to obtain a second solution, and mixing the first solution and the second solution to obtain a transition metal solution;

[0069] (3) The transition metal solution was added dropwise to solution A, the pH of the solution was adjusted to 7, and the mixture was stirred at 70°C for 3 h at a stirring speed of 200 rpm;

[0070] (4) After the stirred solution is completely dried, it is ground evenly and placed in a muffle furnace to obtain the final product. The temperature is raised to 800°C at 5°C / min, calcined for 12 hours, and then naturally cooled and ground to obtain the lithium-rich manganese-based positive electrode material Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 The surface of O2 is coated with a composite cathode material of perovskite-type oxide, the chemical formula of which is Li 0.25 Sr 0.625 Zr 0.5 Nb 0.5 O3, the ionic conductivity of perovskite oxide is 3.22×10 -5 S / cm, the mass ratio of lithium-rich manganese-based cathode material to perovskite-type oxide is 1:0.02, and the lithium ion diffusion coefficient of the composite cathode material during charging is 10 -13.14 cm 2 / s, the lithium ion diffusion coefficient of the composite cathode material during discharge is 10 -12.16 cm 2 / s.

[0071] Example 5

[0072] The difference from Example 1 is that the lithium-rich manganese-based positive electrode material Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 The mass of O2 is 3.33g, and a composite positive electrode material is finally obtained. The mass ratio of lithium-rich manganese-based positive electrode material to perovskite-type oxide is 1:0.03.

[0073] Example 6

[0074] The difference from Example 1 is that the mass of strontium nitrate is 336.5 mg, the mass of zirconium oxynitrate is 295 mg, and the mass of niobium pentoxide is 169.5 mg; finally, a composite positive electrode material is obtained, and the mass ratio of the lithium-rich manganese-based positive electrode material to the perovskite-type oxide is 1:0.05.

[0075] Example 7

[0076] The difference from Example 1 is that the addition of cobalt sulfate heptahydrate is eliminated, the mass of nickel sulfate hexahydrate is 6.87g, and the mass of manganese sulfate tetrahydrate is 17.5g, to obtain a lithium-rich manganese-based positive electrode material Li 1.2 Mn 0.6 Ni 0.2O2, and finally obtain a composite positive electrode material.

[0077] Example 8

[0078] The difference from Example 1 is that the mass of nickel sulfate hexahydrate is 3.42g, the mass of manganese sulfate tetrahydrate is 14.5g, and the mass of cobalt sulfate heptahydrate is 7.31g, and the lithium-rich manganese-based positive electrode material Li 1.2 Mn 0.50 Co 0.20 Ni 0.10 O2, and finally obtain a composite positive electrode material.

[0079] Example 9

[0080] The difference from Example 1 is that the mixing treatment temperature is 50° C., the mixing treatment time is 6 h, and the stirring speed is 350 rpm, and finally a composite positive electrode material is obtained.

[0081] Example 10

[0082] The difference from Example 1 is that the mixing treatment temperature is 80° C., the mixing treatment time is 4 h, and the stirring speed is 100 rpm, and finally a composite positive electrode material is obtained.

[0083] Example 11

[0084] The difference from Example 1 is that the mixing treatment temperature is 90° C., the mixing treatment time is 2 h, and the stirring speed is 50 rpm, and finally a composite positive electrode material is obtained.

[0085] Example 12

[0086] The difference from Example 1 is that the heating rate of the calcination treatment is 10° C. / min, the calcination treatment temperature is 600° C., and the calcination treatment holding time is 20 h, and finally a composite positive electrode material is obtained.

[0087] Example 13

[0088] The difference from Example 1 is that the heating rate of the calcination treatment is 2° C. / min, the calcination treatment temperature is 1000° C., and the calcination treatment holding time is 8 h, and finally a composite positive electrode material is obtained.

[0089] Example 14

[0090] The difference from Example 1 is that the heating rate of the calcination treatment is 12° C. / min, the calcination treatment temperature is 1100° C., and the calcination treatment holding time is 6 h, and finally a composite positive electrode material is obtained.

[0091] Comparative Example 1

[0092] The difference from Example 1 is that the perovskite oxide is eliminated to remove the lithium-rich manganese-based positive electrode material Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2 coating directly uses the lithium-rich manganese-based positive electrode material as the final positive electrode material.

[0093] Comparative Example 2

[0094] The difference from Example 1 is that the amount of strontium nitrate used is 45.4 mg, the amount of zirconium oxynitrate used is 15.3 mg, and the amount of niobium pentoxide used is 59.2 mg. Finally, the lithium-rich manganese-based positive electrode material Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 The surface of O2 is coated with a composite cathode material of perovskite-type oxide, the chemical formula of which is Li 0.45 Sr 0.325 Zr 0.1 Nb 0.9 O3.

[0095] Battery preparation

[0096] The positive electrode materials prepared in the above examples and comparative examples were mixed with acetylene black and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) solvent was added, and the resulting slurry was coated onto an aluminum foil current collector and dried in a vacuum oven at 80°C for 12 hours. A tablet press was used to produce 10mm diameter discs for the positive electrode. A 0.5mm thick, 14mm diameter lithium sheet was used as the negative electrode. A Celgard 2500 separator was used to produce 18mm diameter discs. The positive and negative separators were assembled in an argon-filled glove box. The electrolyte was a 1 mol / L lithium hexafluorophosphate (LiPF6) solution (the solvent was a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a 1:1:1 volume ratio). Coin-type batteries were prepared.

[0097] Performance Testing

[0098] The positive electrode materials prepared in the examples and comparative examples were subjected to a constant current intermittent titration (GITT) test. The test conditions were as follows: the battery was charged at a constant current rate of 0.1C for 10 minutes on a Neware test system, relaxed for 60 minutes, and cycled until the voltage limit of 4.8V was reached; and then discharged at a constant current rate of 0.1C for 10 minutes, relaxed for 60 minutes, and cycled until the voltage limit of 2V was reached. A lithium ion diffusion performance diagram during the charge and discharge process was obtained.

[0099] The batteries prepared in the above examples and comparative examples were tested for their initial discharge capacity at 0.1C, and their initial coulombic efficiency at 0.1C was calculated. The batteries were also tested for their discharge capacity after 150 cycles at 0.5C, and their capacity retention after 150 cycles was calculated. The test results are shown in Table 1.

[0100] Table 1

[0101]

[0102]

[0103] The data in Table 1 show that the cathode material obtained in the present invention has an initial discharge capacity of over 260 mAh / g at 0.1C, and maintains a capacity retention rate of no less than 80% after 150 cycles, significantly improving the cycling performance of the material compared to Comparative Example 1. A comparison of Examples 1 to 3 shows that increasing the Li content enhances both the electrical conductivity and ionic conductivity, improving the cycling performance of the material to a certain extent.

[0104] Figure 1 The XRD comparison diagram of the positive electrode materials of Example 1 and Comparative Example 1 of the present application is shown in FIG. Figure 1 It can be seen that both Comparative Example 1 and Example 1 exhibit an α-NaFeO2 structure with an "R3m" space group. The weak diffraction peak near 23° corresponds to the superlattice structure of the Li2MnO3 phase. The main phases of the Example and Comparative Example correspond to the layered structure of the lithium-rich manganese-based material (PDF#46-0446). Example 1 exhibits a low-intensity diffraction peak near 34°, corresponding to the strongest peak of the perovskite oxide SrTiO3, indicating that a perovskite oxide coating has been constructed on the surface of Example 1.

[0105] Figure 2 The lithium ion diffusion performance diagram of the positive electrode material of Example 1 and Comparative Example 1 of the present application during the charging process is shown in FIG. Figure 2 It can be calculated that the lithium ion diffusion coefficient of the positive electrode material of Example 1 during the charging process is 10 -12.82 cm 2 / s, the lithium ion diffusion coefficient of the positive electrode material of Comparative Example 1 during the charging process is 10 -13.38 cm 2 / s.

[0106] Figure 3 The lithium ion diffusion performance diagram of the positive electrode material of Example 1 and Comparative Example 1 of the present application during the discharge process is shown in FIG. Figure 3 It can be calculated that the lithium ion diffusion coefficient of the positive electrode material of Example 1 during the discharge process is 10 -11.56 cm 2 / s, the lithium ion diffusion coefficient of the positive electrode material of Comparative Example 1 during the discharge process is 10 -13.09 cm 2 / s.

[0107] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0108] The perovskite oxide of the present application has high ionic conductivity, a wide electrochemical platform and a stable structure. Coating it on the surface of the lithium-rich manganese-based positive electrode material can help reduce the contact between the lithium-rich manganese-based positive electrode material and the electrolyte, thereby helping to reduce the generation of side reactions, and on the other hand, help to improve the first coulombic efficiency. And Li 2x- y Sr 1-x Zr 1-y Nb y As a lithium ion conductor with low grain boundary resistance, O3 can play a positive role in improving lithium diffusion efficiency, helping to improve the conductivity of lithium-rich manganese-based positive electrode materials, reduce the lithium ion transfer impedance between liquid and solid phases, and enhance rate performance. 2x-y Sr 1-x Zr 1-y Nb y The O3 coating layer interface is a cubic perovskite structure with nano-scale defects and a large number of A-site defects. As the cycle progresses, the loss of Li and the dissolution of transition metals will cause oxygen vacancies in the coating layer. Due to the anionic redox mechanism of the lithium-rich manganese-based cathode material, oxygen will be released during the cycle, causing the structure of the cathode material itself to decay, resulting in rapid capacity decay during the cycle. 2x-y Sr 1-x Zr 1-y Nb y The presence of the O3 coating layer can fix the incompletely released oxygen in the oxygen vacancies of the coating layer, inhibit the release of oxygen, and slow down the capacity decay and structural degradation of the lithium-rich manganese-based cathode material during cycling. 2x-y Sr 1-x Zr 1-y Nb y Too large or too small y in O3 is not conducive to improving the ionic conductivity of the composite positive electrode material. Controlling the value of y within the range of 0.5 to 0.7 helps to further improve the ionic conductivity of the composite positive electrode material and improve the structural stability of the composite positive electrode material, thereby helping to further improve the first-cycle coulombic efficiency and cycle stability of the composite positive electrode material.

[0109] The above are merely embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A composite positive electrode material, characterized in that The composite positive electrode material comprises a lithium-rich manganese-based positive electrode material and a perovskite-type oxide coated on the surface of the lithium-rich manganese-based positive electrode material. The chemical formula of the perovskite-type oxide is Li 2x-y Sr 1-x Zr 1-y Nb y O3, where x=3y / 4, y=0.5~0.

7.

2. The composite cathode material according to claim 1, characterized in that The mass ratio of the lithium-rich manganese-based positive electrode material to the perovskite-type oxide is 1:(0.01-0.03); preferably, the chemical formula of the lithium-rich manganese-based positive electrode material is Li[Li 1-a-b-c Mn a Co b Ni c O2, where a + b + c = 0.8, a = 0.50 - 0.60, b = 0.10 - 0.15, and c = 0.10 - 0.

15.

3. The positive electrode material according to claim 1 or 2, characterized in that The ionic conductivity of the perovskite oxide is 2.04×10 -5 ~3.62×10 -5 S / cm.

4. A method for preparing the composite cathode material according to any one of claims 1 to 3, characterized in that: The preparation method comprises: Step S1, mixing raw materials including a lithium-rich manganese-based positive electrode material, a strontium source, a zirconium source, a niobium source and water to obtain a precursor; Step S2: calcining the precursor to obtain the composite positive electrode material.

5. The preparation method according to claim 4, characterized in that The temperature of the mixing treatment is 50 to 80° C.; and / or the time of the mixing treatment is 3 to 6 hours.

6. The preparation method according to claim 4 or 5, characterized in that The mixing process is performed under stirring, and the stirring speed of the mixing process is 100 to 350 rpm.

7. The preparation method according to any one of claims 4 to 6, characterized in that The heating rate of the calcination treatment is 2 to 10° C. / min; and / or the temperature of the calcination treatment is 600 to 1000° C.; and / or the holding time of the calcination treatment is 8 to 20 hours.

8. The preparation method according to any one of claims 4 to 7, characterized in that The pH value of the solution in the mixing treatment is 6.5-7.5; and / or the strontium source is selected from any one or more of strontium nitrate, strontium oxalate and strontium acetate; and / or the zirconium source is selected from any one or more of zirconium oxynitrate, zirconium nitrate and zirconium oxide; and / or the niobium source is niobium pentoxide and / or ammonium niobium oxalate.

9. A positive electrode sheet comprising a current collector and a positive electrode active layer, characterized in that: The positive electrode active layer contains the composite positive electrode material according to any one of claims 1 to 3.

10. A lithium-ion battery comprising a positive electrode, an electrolyte and a negative electrode, characterized in that: The positive electrode sheet is the positive electrode sheet according to claim 9.

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