Lithium ion battery composite cathode material and preparation method thereof

Abstract

This invention discloses a composite cathode material for lithium-ion batteries and its preparation method, comprising a cathode active material and a lithium oxide solid electrolyte material. The lithium oxide solid electrolyte material contains a small amount of sodium ions, and the surface of the cathode active material is coated with the lithium oxide solid electrolyte material while being internally doped with sodium ions. This invention first synthesizes a lithium oxide solid electrolyte material containing a small amount of sodium ions via a lithium-sodium ion exchange method, and then prepares the composite cathode material by simply mixing it with the cathode active material followed by heat treatment. The composite cathode material provided by this invention has the synergistic benefits of both solid electrolyte coating and sodium ion doping, significantly improving the capacity, rate performance, and cycle performance of the cathode material, and the preparation process is simple and controllable.

Description

Technical Field

[0001] This invention belongs to the field of electrochemistry, specifically relating to a composite cathode material for lithium-ion batteries and its preparation method. Background Technology

[0002] In recent decades, the rapid rise of lithium-ion (Li-ion) batteries has not only reshaped the vast market for portable electronics (such as mobile phones, smartwatches, and laptops) and promoted the efficient use of clean energy, but also facilitated the commercialization of electric vehicles (EVs), further alleviating the growing environmental crisis caused by heavy reliance on fossil fuels and carbon dioxide emissions. Therefore, lithium-ion batteries are indispensable in numerous applications, including portable electronics, electric vehicles, and large-scale energy storage. In lithium-ion batteries, the properties of the cathode material play a decisive role in the overall battery performance, especially high-energy-density cathode active materials such as lithium nickel manganese cobalt oxide, lithium-rich manganese-based oxides, and high-voltage lithium cobalt oxide. However, these high-energy-density cathode active materials are prone to breakage during cycling and exhibit continuous side reactions with the electrolyte, which severely impairs the battery's cycle life and rate performance. Surface coating is an important strategy to effectively improve the stability of cathode materials. Its specific functions include: 1) physical barrier to suppress side reactions; 2) removal of hydrofluoric acid (HF) to prevent chemical corrosion of electrolyte and reduce transition metal dissolution; 3) enhancement of electronic and ionic conductivity; 4) surface chemical modification to promote interfacial ion charge transfer; and 5) stabilization of structure to reduce phase transition stress.

[0003] Solid electrolytes exhibit high ionic conductivity and low electronic conductivity at room temperature, making them suitable as cathode coating layers. Due to their high ionic conductivity, they are expected to improve charge transfer at the cathode / electrolyte interface. Furthermore, solid electrolyte coating provides a physical barrier, suppressing side reactions. Chinese invention patent application CN108448055A coats the cathode material with a continuous solid electrolyte film to improve the cathode material's performance and suppress expansion; Chinese invention patent application CN109449414A provides a core-shell structure for solid electrolyte coating of the cathode material, which can improve the interface problem between the cathode and the solid electrolyte. Both of these invention patents suppress side reactions between the cathode material and the electrolyte from the perspective of building a physical barrier, but they cannot suppress the cracking and pulverization of the cathode material particles themselves from a structural perspective. Chinese invention patent application CN 112310353A discloses a composite cathode material for lithium-ion batteries. This composite cathode material is obtained by filling / embedding a solid electrolyte into the bulk cathode material. It effectively improves the density, coulombic efficiency, rate performance and cycle life of the cathode material, effectively suppresses cracking and pulverization of the material during cycling, and can also stabilize the crystal structure of the material. However, the preparation process of this invention patent is complicated. The introduction of solid electrolyte needs to start from the cathode material precursor preparation step, which is not conducive to the expansion of scale and cost reduction. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, the present invention aims to provide a composite cathode material for lithium-ion batteries and its preparation method. This composite cathode material is formed by a simple physical mixing and subsequent heat treatment of a lithium oxide-lithium ion solid electrolyte containing a small amount of sodium ions and a cathode active material. The lithium oxide-lithium ion solid electrolyte forms a coating layer on the surface of the cathode active material, while the small amount of sodium ions in the lithium oxide-lithium ion solid electrolyte reacts with the lithium ions in the cathode active material to form a Li-ion reaction. + / Na + The exchange process not only doped sodium ions into the bulk of the composite cathode material particles but also generated sodium metal oxide crystals on its surface. This composite cathode material exhibits the synergistic benefits of both solid-state electrolyte coating and sodium ion doping modification. It not only provides a physical barrier of high ionic conductivity and low electronic conductivity on the cathode material surface but also, from a structural perspective, suppresses cracking and pulverization of the cathode material during cycling, stabilizing the crystal lattice structure. + / Na + More free Li released by the exchange + It can also enable the cathode material to achieve higher capacity, significantly improving the capacity performance, rate performance and cycle performance of the cathode material.

[0005] To achieve the above objectives, the present invention provides a composite cathode material for lithium-ion batteries, comprising a cathode active material, wherein the composite cathode material further comprises a lithium oxide solid electrolyte material, the lithium oxide solid electrolyte material contains a small amount of sodium ions, the surface of the cathode active material is coated with the lithium oxide solid electrolyte material, and sodium ions are doped inside.

[0006] The preparation method of the composite cathode material includes the following steps:

[0007] S1. Accurately weigh the positive electrode active material and the oxide lithium-ion solid electrolyte material according to the proportion;

[0008] S2. The materials weighed in S1 are mixed and ball-milled to obtain a mixed material;

[0009] S3. Place the mixed material described in S2 in a tube furnace, introduce oxygen, and calcine at 600-1000℃ for 8-12 hours to obtain the high-capacity lithium-ion battery composite cathode material.

[0010] The formation of Na metal oxide crystals on the surface of the composite cathode material is achieved through lithium-sodium ion exchange between sodium ions in the oxide lithium-ion solid electrolyte material and the surface of the cathode active material.

[0011] The oxide lithium-ion solid electrolyte material is obtained by liquid-phase lithium-sodium ion exchange experiments using sodium ion conductors as precursors. The preparation method includes the following steps:

[0012] A1. Sodium ion conductor, lithium bis(trifluoromethanesulfonyl)imide, and ionic liquid are mixed evenly and placed in a reaction vessel. The concentration of lithium bis(trifluoromethanesulfonyl)imide in the ionic liquid is 0.1 mol / L-0.5 mol / L, and the molar ratio of lithium bis(trifluoromethanesulfonyl)imide to sodium ion conductor is 3:1. The reaction vessel is placed in a homogeneous reactor and stirred at a speed of 50 rpm / min for 72-144 h at a temperature of 100-200℃.

[0013] A2. The product in the reactor is removed, centrifuged, dried, and calcined at 400-500℃ to obtain the oxide lithium-ion solid electrolyte material.

[0014] Preferably, the ionic liquid in step A1 is any one or more of imidazole ionic liquids, quaternary ammonium ionic liquids, and pyrrole ionic liquids.

[0015] Preferably, the ionic liquid in step A1 comprises 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

[0016] Preferably, the average particle size of the positive electrode active material is 5μm≤D50≤20μm, and the average particle size of the oxide lithium-ion solid electrolyte material is 50nm≤D50≤500nm.

[0017] Preferably, the oxide lithium-ion solid electrolyte material accounts for 0.5 wt.% to 3 wt.% of the composite cathode material.

[0018] Preferably, the positive electrode active material is any one of lithium cobalt oxide, olivine type, lithium nickel cobalt manganese oxide, lithium-rich manganese-based oxide, and spinel oxide.

[0019] Preferably, the oxide solid electrolyte material is Li. 3-x Na x Zr2Si2PO 12 Li 3-x Na x V2(PO4)3, Li 3- x Na x La(PO4)2, Li 3-x Na x Hf2Si2PO 12 Li 4-y Na y Zr2(SiO4)3, Li 1-z Na z Zr2(PO4)3, Li 1.3-m Na m M 0.3 Ti 1.7 (PO4)3 or Li 1.3-m Na m Al 0.3 Ge 1.7 Any of (PO4)3, where M is Al, Cr, Ga, Ge, Sc, In, Lu, Y, or La, 0 <x<0.3,0<y<0.4,0<z<0.1,0<m<0.1。

[0020] This invention also provides the application of the lithium-ion battery composite cathode material prepared by the method. The composite cathode material is formed by a simple physical mixing and subsequent heat treatment of an oxide lithium-ion solid electrolyte containing a small amount of sodium ions and a cathode active material. The oxide lithium-ion solid electrolyte forms a coating layer on the surface of the cathode active material, while the small amount of sodium ions in the oxide lithium-ion solid electrolyte reacts with the lithium ions in the cathode active material to form a Li-ion reaction. + / Na +The exchange process not only doped sodium ions into the bulk of the composite cathode material particles but also generated sodium metal oxide crystals on its surface. This composite cathode material exhibits the synergistic benefits of both solid-state electrolyte coating and sodium ion doping modification. It not only provides a physical barrier of high ionic conductivity and low electronic conductivity on the cathode material surface but also, from a structural perspective, suppresses cracking and pulverization during cycling, stabilizing the crystal lattice structure. + / Na + More free Li released by the exchange + It can also enable the cathode material to achieve higher capacity, significantly improve the capacity performance, rate performance and cycle performance of the cathode material, and realize a high-energy-density and high-stability all-solid-state lithium metal battery that can operate at room temperature without any electrode modification.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The oxide lithium-ion solid electrolyte used in this invention is obtained by liquid-phase lithium-sodium ion exchange experiment with sodium ion conductor as precursor. Since it inherits the framework structure of sodium ion conductor, the transport of lithium ions in it is faster and more convenient. The resulting lithium-ion solid electrolyte has high ionic conductivity. Therefore, after forming the coating layer, it can not only prevent the dissolution and corrosion of the positive electrode material, but also improve the charge transfer at the interface, reduce the resistance of the positive electrode material and increase the electrochemical reaction rate, so that the positive electrode material exhibits excellent rate performance and higher capacity retention.

[0023] (2) This invention uses a heat treatment method to remove a small amount of Na from the oxide lithium-ion solid electrolyte. + Some ions are doped into the bulk of the composite cathode material particles, while others are incorporated through Li... + and Na + The exchange of Na forms Na metal oxide crystals on the surface of the composite cathode material particles, while various defects are formed near the surface. First, Na... + Doping can effectively increase the interlayer spacing, which is beneficial for the diffusion of lithium ions between layers and improves capacity; Na + Doping can effectively suppress Li x Ni 1-x The formation of the O impurity phase increases the Ni / Mn disorder, reduces charge transfer resistance, and accelerates lithium-ion diffusion, thereby improving the rate performance of the material; Na + Doping acts as a support, preventing structural collapse and improving the stability of the material structure. Secondly, the Na metal oxide crystal coating on the surface prevents electrolyte dissolution and corrosion of the cathode material, thus providing protection. Furthermore, the stacking fault defects it induces achieve a pinning effect, maintaining the layered structure. Li + / Na +More free Li released by the exchange + This allows the cathode material to achieve a higher capacity.

[0024] (3) This invention provides a novel method for sodium doping modification. + Doping can effectively improve the stability of material structure, but controlling Na... + The doping amount is crucial; low sodium-doped lithium-ion cathode materials often exhibit poor cycle stability, while high sodium doping... + Furthermore, sodium doping can cause severe deformation and distortion of the cathode material structure, reducing its capacity. Traditional sodium doping is typically added during the synthesis of lithium-ion cathode material precursors, leading to sodium source loss in subsequent synthesis steps and making precise control of the sodium doping content impossible. In contrast, the sodium in this invention is present in the oxide-based lithium-ion solid electrolyte, which is obtained through liquid-phase lithium-sodium ion exchange experiments using a sodium-ion conductor as a precursor. The sodium content can be precisely controlled through the ion exchange rate. Subsequent preparation processes involving the composite with lithium-ion cathode materials only involve physical mixing and heat treatment steps, eliminating sodium source loss. Therefore, this invention develops a novel, simple, effective, and controllable sodium ion doping method.

[0025] (4) The composite cathode material provided by the present invention can achieve excellent capacity performance, rate performance and cycle performance when applied to lithium-ion batteries. At the same time, the preparation process is green and efficient, the preparation process is simple and the application range is wide, and it can be mass-produced industrially. Attached Figure Description

[0026] To more clearly illustrate the technical solutions disclosed in this invention, the accompanying drawings used in the description of some embodiments of this invention will be briefly introduced below. Obviously, the drawings described below are only drawings of some embodiments of this invention, and those skilled in the art can obtain other drawings based on these drawings. In the drawings:

[0027] Figure 1 This is a SEM-Mapping image of the oxide lithium-ion solid electrolyte prepared in Example 1 of the present invention;

[0028] Figure 2 This is a SEM image of the lithium-ion battery composite cathode material prepared in Example 1 of the present invention;

[0029] Figure 3 The image shows the XRD pattern of the lithium-ion battery composite cathode material prepared in Example 1 of this invention.

[0030] Figure 4The first-cycle charge-discharge curves of lithium-ion batteries prepared using the composite cathode material and the uncoated cathode material of Example 1 are shown.

[0031] Figure 5 The graphs show the rate performance of lithium-ion batteries made using the composite cathode material and the uncoated cathode material of Example 1.

[0032] Figure 6 The graphs show the cycle performance of lithium-ion batteries made using the composite cathode material and the uncoated cathode material of Example 1. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0034] This invention provides a composite cathode material for lithium-ion batteries, comprising a cathode active material and a lithium oxide solid electrolyte material. The lithium oxide solid electrolyte material contains a small amount of sodium ions, and the surface of the cathode active material is coated with the lithium oxide solid electrolyte material while being doped with sodium ions internally.

[0035] The preparation method of the composite cathode material includes the following steps:

[0036] S1. Accurately weigh the positive electrode active material and the oxide lithium-ion solid electrolyte material according to the proportion;

[0037] S2. The materials weighed in S1 are mixed and ball-milled to obtain a mixed material;

[0038] S3. Place the mixed material described in S2 in a tube furnace, introduce oxygen, and calcine at 600-1000℃ for 8-12 hours to obtain the high-capacity lithium-ion battery composite cathode material.

[0039] The formation of Na metal oxide crystals on the surface of the composite cathode material is achieved through lithium-sodium ion exchange between sodium ions in the oxide lithium-ion solid electrolyte material and the surface of the cathode active material.

[0040] The oxide lithium-ion solid electrolyte material is obtained by liquid-phase lithium-sodium ion exchange experiments using sodium ion conductors as precursors. The preparation method includes the following steps:

[0041] A1. Sodium ion conductor, lithium bis(trifluoromethanesulfonyl)imide, and ionic liquid are mixed evenly and placed in a reaction vessel. The concentration of lithium bis(trifluoromethanesulfonyl)imide in the ionic liquid is 0.1 mol / L-0.5 mol / L, and the molar ratio of lithium bis(trifluoromethanesulfonyl)imide to sodium ion conductor is 3:1. The reaction vessel is placed in a homogeneous reactor and stirred at a speed of 50 rpm / min for 72-144 h at a temperature of 100-200℃.

[0042] A2. The product in the reactor is removed, centrifuged, dried, and calcined at 400-500℃ to obtain the oxide lithium-ion solid electrolyte material.

[0043] Preferably, the ionic liquid in step A1 is any one or more of imidazole ionic liquids, quaternary ammonium ionic liquids, and pyrrole ionic liquids.

[0044] Preferably, the ionic liquid in step A1 comprises 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

[0045] Preferably, the average particle size of the positive electrode active material is 5μm≤D50≤20μm, and the average particle size of the oxide lithium-ion solid electrolyte material is 50nm≤D50≤500nm.

[0046] Preferably, the oxide lithium-ion solid electrolyte material accounts for 0.5 wt.% to 3 wt.% of the composite cathode material.

[0047] Preferably, the positive electrode active material is any one of lithium cobalt oxide, olivine type, lithium nickel cobalt manganese oxide, lithium-rich manganese-based oxide, and spinel oxide.

[0048] Preferably, the oxide solid electrolyte material is Li. 3-x Na x Zr2Si2PO 12 Li 3-x Na x V2(PO4)3, Li 3- x Na x La(PO4)2, Li 3-x Na x Hf2Si2PO 12 Li 4-y Na y Zr2(SiO4)3, Li 1-z Na z Zr2(PO4)3, Li 1.3-m Na m M 0.3 Ti 1.7 (PO4)3 or Li 1.3-m Nam Al 0.3 Ge 1.7 Any of (PO4)3, where M is Al, Cr, Ga, Ge, Sc, In, Lu, Y, or La, 0 <x<0.3,0<y<0.4,0<z<0.1,0<m<0.1。

[0049] Example 1:

[0050] This embodiment provides a composite cathode material for lithium-ion batteries, including the cathode active material lithium nickel cobalt manganese oxide (LiNi). 0.8 Co 0.1 Mn 0.1 The composite cathode material (O2, NCM811) also includes the oxide lithium-ion solid electrolyte material Li. 2.5 Na 0.5 Zr2Si2PO 12 The surface of the positive electrode active material is coated with an oxide lithium-ion solid electrolyte material, and sodium ions are doped inside.

[0051] The oxide lithium-ion solid electrolyte material Li 2.5 Na 0.5 Zr2Si2PO 12 It is a sodium ion conductor Na3Zr2Si2PO 12 The precursor, obtained through liquid-phase lithium-sodium ion exchange experiments, is prepared by the following steps:

[0052] (1) Sodium ion conductor Na3Zr2Si2PO 12 The mixture of lithium bis(trifluoromethanesulfonyl)imide and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt was homogeneous and placed in a reaction vessel. The concentration of lithium bis(trifluoromethanesulfonyl)imide in the ionic liquid was 0.5 mol / L. The mixture was then reacted with Na3Zr2Si2PO4. 12 The molar ratio is 3:1; the reaction vessel is placed in a homogeneous reactor and stirred at a speed of 50 rpm / min for 68 hours at a temperature of 180℃.

[0053] (2) The product in the reactor was removed, centrifuged, dried, and calcined at 450℃ to obtain the oxide lithium-ion solid electrolyte material Li. 2.5 Na 0.5 Zr2Si2PO 12 .

[0054] Figure 1This is a SEM-mapped image of the oxide lithium-ion solid electrolyte prepared in Example 1 of this invention. As can be seen from the image, the prepared lithium-ion oxide solid electrolyte contains a small amount of Na. Based on the atomic ratio, the chemical formula of the solid electrolyte is calculated to be Li. 2.5 Na 0.5 Zr2Si2PO 12 .

[0055] The preparation method of the composite cathode material includes the following steps:

[0056] (1) Accurately weigh the positive electrode active material lithium nickel cobalt manganese oxide (LiNi) at a mass ratio of 98:2. 0.8 Co 0.1 Mn 0.1 O2, NCM811) and oxide lithium-ion solid electrolyte material Li 2.5 Na 0.5 Zr2Si2PO 12 ;

[0057] (2) Mix the materials weighed in step (1) and ball mill for half an hour to obtain a mixed material;

[0058] (3) The mixed material from step (2) is placed in a tube furnace, oxygen is introduced, and it is calcined at 600°C for 12 hours to obtain a high-capacity lithium-ion battery composite cathode material.

[0059] Figure 2 This is a SEM image of the lithium-ion battery composite cathode material prepared in Example 1 of the present invention. It can be seen from the image that Li... 2.5 Na 0.5 Zr2Si2PO 12 Uniformly coated on the surface of lithium nickel cobalt manganese oxide cathode material, with rod-shaped crystals growing on the surface, this is due to Na + Ions through Li + and Na + The exchange of Na metal oxide crystals forms on the surface of the composite cathode material particles, while various defects are formed near the surface, releasing more free Li. + This allows the cathode material to achieve a higher capacity.

[0060] Figure 3 The image shows the XRD pattern of the lithium-ion battery composite cathode material prepared in Example 1 of this invention. As can be seen from the image, the composite material exhibits NCM811 and Li... 2.5 Na 0.5 Zr2Si2PO 12 In addition to the characteristic diffraction peaks, another characteristic diffraction peak was observed at 13.8°, which can be attributed to sodium metal oxides (specifically, Na...).0.7 MnO 2.05 (JCPDS card no. 27-0751). This directly proves that Li₂ occurred at the surface of the NCM811 cathode material. + / Na + Ion exchange.

[0061] Example 2:

[0062] This embodiment provides a composite cathode material for lithium-ion batteries, including a cathode active material, lithium-rich manganese-based oxide (Li₂O₃). 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2), the composite cathode material also includes lithium oxide lithium-ion solid electrolyte material Li 2.3 Na 0.7 La(PO4)2, the positive electrode active material is coated with an oxide lithium-ion solid electrolyte material, and sodium ions are doped inside.

[0063] The oxide lithium-ion solid electrolyte material Li 2.3 Na 0.7 La(PO4)2 was obtained by liquid-phase lithium-sodium ion exchange experiments using sodium ion conductor Na3La(PO4)2 as a precursor. The preparation method includes the following steps:

[0064] (1) Sodium ion conductor Na3La(PO4)2 is mixed evenly with lithium bis(trifluoromethanesulfonyl)imide and ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and placed in a reaction vessel. The concentration of lithium bis(trifluoromethanesulfonyl)imide in the ionic liquid is 0.5 mol / L, and the molar ratio with Na3La(PO4)2 is 2:1. The reaction vessel is placed in a homogeneous reactor and stirred at a speed of 50 rpm / min for 32 h at a temperature of 120℃.

[0065] (2) The product in the reactor was removed, centrifuged, dried, and calcined at 400℃ to obtain the oxide lithium-ion solid electrolyte material Li. 2.3 Na 0.7 La(PO4)2.

[0066] The preparation method of the composite cathode material includes the following steps:

[0067] (1) Accurately weigh the positive electrode active material, lithium-rich manganese-based oxide (Li), at a mass ratio of 95:5. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2) and oxide lithium-ion solid electrolyte materials Li 2.3 Na0.7 La(PO4)2;

[0068] (2) Mix the materials weighed in step (1) and ball mill for half an hour to obtain a mixed material;

[0069] (3) The mixed material from step (2) is placed in a tube furnace, oxygen is introduced, and it is calcined at 600°C for 8 hours to obtain a high-capacity lithium-ion battery composite cathode material.

[0070] Figure 4 The figures show the first-cycle charge-discharge curves of lithium-ion batteries made using the composite cathode material and the uncoated cathode material of Example 2. The first-cycle discharge capacity of the uncoated single cathode material is 302.2 mAh / g. After coating with solid electrolyte material, the first-cycle discharge capacity of the composite cathode material increases to 329.0 mAh / g. It can be seen that the capacity performance of the composite cathode material of the present invention is significantly improved.

[0071] Figure 5 The graphs show the rate performance curves of lithium-ion batteries prepared using the composite cathode material and the uncoated cathode material from Example 1. As can be seen from the graphs, at different rates, the capacity performance of the composite cathode material coated with solid electrolyte is higher than that of the uncoated single cathode material. At a discharge rate of 1C, the discharge capacity of the uncoated single cathode material is 222.4 mAh / g, while the 1C discharge capacity of the composite cathode material increases to 299.1 mAh / g. This demonstrates that coating with solid electrolyte improves the capacity of lithium-ion batteries. + Its rapid transmission capability enhances the rate performance of the cathode material.

[0072] Example 3:

[0073] This embodiment provides a composite cathode material for lithium-ion batteries, including the cathode active material lithium nickel cobalt manganese oxide (LiNi). 0.8 Co 0.1 Mn 0.1 The composite cathode material (O2, NCM811) also includes the oxide lithium-ion solid electrolyte material Li. 1.2 Na 0.1 Al 0.3 Ti 1.7 (PO4)3, the surface of the positive electrode active material is coated with an oxide lithium-ion solid electrolyte material, and sodium ions are doped inside.

[0074] The oxide lithium-ion solid electrolyte material Li 1.2 Na 0.1 Al 0.3 Ti 1.7 (PO4)3 is a sodium ion conductor Na 1.3 Al 0.3Ti 1.7 (PO4)3 was used as a precursor and obtained through a liquid-phase lithium-sodium ion exchange experiment. The preparation method includes the following steps:

[0075] (1) Sodium ion conductor Na 1.3 Al 0.3 Ti 1.7 (PO4)3 is mixed thoroughly with lithium bis(trifluoromethanesulfonyl)imide and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and then placed in a reaction vessel. The concentration of lithium bis(trifluoromethanesulfonyl)imide in the ionic liquid is 1 mol / L, and it reacts with Na... 1.3 Al 0.3 Ti 1.7 The molar ratio of (PO4)3 is 3:1; the reaction vessel is placed in a homogeneous reactor and stirred at a speed of 50 rpm / min for 72 h at a temperature of 180℃.

[0076] (2) The product in the reactor was removed, centrifuged, dried, and calcined at 400℃ to obtain the oxide lithium-ion solid electrolyte material Li. 1.2 Na 0.1 Al 0.3 Ti 1.7 (PO4)3.

[0077] The preparation method of the composite cathode material includes the following steps:

[0078] (1) Accurately weigh the positive electrode active material lithium nickel cobalt manganese oxide (LiNi) at a mass ratio of 97:3. 0.8 Co 0.1 Mn 0.1 O2, NCM811) and oxide lithium-ion solid electrolyte material Li 1.2 Na 0.1 Al 0.3 Ti 1.7 (PO4)3;

[0079] (2) Mix the materials weighed in step (1) and ball mill for half an hour to obtain a mixed material;

[0080] (3) The mixed material from step (2) is placed in a tube furnace, oxygen is introduced, and it is calcined at 900°C for 10 hours to obtain a high-capacity lithium-ion battery composite cathode material.

[0081] Figure 6The figures show the cycle performance curves of lithium-ion batteries prepared using the composite cathode material of Example 3 and the uncoated cathode material at a high temperature of 55°C. After coating with a solid electrolyte, the capacity retention rate of the material after 100 cycles increased from 58.1% to 84.7%. It can be seen that coating with a solid electrolyte greatly improves the interfacial structural stability and electrochemical stability of lithium-ion batteries based on high-nickel materials.

[0082] In summary, the composite cathode material for lithium-ion batteries provided by this invention combines two modification methods—solid electrolyte coating and sodium ion doping—by coating a small amount of sodium-containing oxide lithium-ion solid electrolyte onto the cathode active material, resulting in synergistic benefits across multiple scales. First, the surface oxide lithium-ion solid electrolyte coating layer prevents electrolyte dissolution and corrosion of the bulk material, improves charge transfer at the interface, reduces the cathode material resistance, and increases the electrochemical reaction rate. Second, the sodium in the bulk of the composite cathode material... + Doping can enhance the stability of the bulk structure through the "pillar-supporting effect," while simultaneously improving the capacity and rate performance of the cathode material. Finally, the Li-based doping on the surface of the composite cathode material particles... + / Na + The exchange formation of sodium metal oxides induces stacking fault defects that can achieve a pinning effect to maintain the layer structure. Therefore, the composite cathode material provided by this invention includes multi-scale modification such as surface coating, bulk doping, and defect control, which effectively suppresses cracking and pulverization of the material during cycling, stabilizes the lattice structure of the material, and effectively improves the discharge capacity, rate performance, and cycle life of the cathode material. At the same time, the synthesis method is simple and controllable, which helps to realize large-scale production.

[0083] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as a limitation of the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention based on the above disclosure without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for preparing a composite cathode material for lithium-ion batteries, characterized in that, The lithium-ion battery composite cathode material includes a cathode active material and a lithium oxide solid electrolyte material. The lithium oxide solid electrolyte material contains sodium ions. The surface of the cathode active material is coated with the lithium oxide solid electrolyte material, and sodium ions are doped inside. The preparation method includes the following steps: S1. Accurately weigh the positive electrode active material and the oxide lithium-ion solid electrolyte material according to the proportion; S2. The materials weighed in S1 are mixed and ball-milled to obtain a mixed material; S3. Place the mixed material described in S2 in a tube furnace, introduce oxygen, and calcine at 600-1000°C for 8-12 hours to obtain the lithium-ion battery composite cathode material. The formation of Na metal oxide crystals on the surface of the composite cathode material is achieved through lithium-sodium ion exchange between sodium ions in the oxide lithium-ion solid electrolyte material and the surface of the cathode active material. The oxide lithium-ion solid electrolyte material is obtained by liquid-phase lithium-sodium ion exchange experiments using sodium ion conductors as precursors. The preparation method includes the following steps: A1. The sodium ion conductor, lithium bis(trifluoromethanesulfonyl)imide, and ionic liquid are mixed evenly and placed in a reaction vessel. The concentration of lithium bis(trifluoromethanesulfonyl)imide in the ionic liquid is 0.1 mol / L-0.5 mol / L, and the molar ratio of lithium bis(trifluoromethanesulfonyl)imide to sodium ion conductor is 3:

1. The reaction vessel is placed in a homogeneous reactor and stirred at a speed of 50 rpm / min for 72-144 h at a temperature of 100-200°C. A2. Remove the product from the reactor and centrifuge it, dry it, and calcine it at 400-500°C to obtain the oxide lithium-ion solid electrolyte material. The ionic liquid mentioned in step A1 is any one or more of imidazole ionic liquids, quaternary ammonium ionic liquids, and pyrrole ionic liquids.

2. The method for preparing the lithium-ion battery composite cathode material according to claim 1, characterized in that, The average particle size of the positive electrode active material is 5μm≤D50≤20μm, and the average particle size of the oxide lithium-ion solid electrolyte material is 50nm≤D50≤500nm.

3. The method for preparing the lithium-ion battery composite cathode material according to claim 1, characterized in that, The oxide lithium-ion solid electrolyte material accounts for 0.5 wt.% to 3 wt.% of the composite cathode material.

4. The method for preparing the lithium-ion battery composite cathode material according to claim 1, characterized in that, The positive electrode active material is any one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium-rich manganese-based oxide, and spinel oxide.

5. The method for preparing the lithium-ion battery composite cathode material according to claim 1, characterized in that, The oxide solid electrolyte material is Li 3-x Na x Zr2Si2PO 12 Li 3-x Na x V2(PO4)3, Li 3-x Na x La(PO4)2, Li 3- x Na x Hf2Si2PO 12 Li 4-y Na y Zr2(SiO4)3, Li 1-z Na z Zr2(PO4)3, Li 1.3-m Na m M 0.3 Ti 1.7 (PO4)3 or Li 1.3- m Na m Al 0.3 Ge 1.7 Any one of (PO4)3, where M is Al, Cr, Ga, Ge, Sc, In, Lu, Y, or La, 0 <x<0.3,0<y<0.4,0<z<0.1,0<m<0.1。 6. The method for preparing the lithium-ion battery composite cathode material according to claim 1, characterized in that, The ionic liquid in step A1 comprises 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

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