Negative electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a negative electrode material and a preparation method and application thereof. The negative electrode material comprises graphite, non-metal ions injected into the graphite through an ion injection method, and a TiO2 coating layer coating the graphite. The negative electrode material disclosed by the invention has the beneficial effects that the negative electrode material combines ion implantation with the surface coating to modify the graphite, so that the electron and ion transmission efficiency in the graphite is optimized, the interface stability is enhanced through the surface coating, and side reactions are reduced; therefore, the comprehensive improvement of high specific capacity, high rate capability and long cycle life of the lithium ion battery is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a negative electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the increasing demand for fast charging in electric vehicles and portable electronic devices, the research on fast charging graphite negative electrode materials for lithium-ion batteries has become a hot topic. Traditional graphite negative electrodes have problems such as slow lithium-ion diffusion rate and many interfacial side reactions during fast charging, which limit their performance. In order to improve the fast charging performance of graphite negative electrodes, researchers have made significant progress from two aspects: the modification of the bulk structure and the surface modification of the microstructure.

[0003] In terms of the modification of the bulk structure, the intrinsic structure of graphite is mainly optimized to shorten the lithium-ion diffusion path. For example, the graphite layer spacing is enlarged by methods such as oxidation, acidification, or etching to increase the lithium-ion diffusion channels. Guo et al. obtained micro-expanded layered graphite by treating with hydrogen peroxide, and its layer spacing was enlarged to 0.336 nm, significantly improving the lithium-ion diffusion rate. In addition, designing conductive graphite with a three-dimensional (3D) structure, such as a vertical porous channel structure, can expose more lithium-ion active sites and further improve the rate performance.

[0004] In terms of surface modification, carbon material coating is one of the common methods. By coating a layer of amorphous carbon on the surface of graphite to form a "core-shell" structure, it can not only avoid direct contact between the electrolyte and graphite, but also increase the lithium-ion diffusion channels and improve the rate performance. In addition, coating with metal or non-metal oxides (such as Al2O3) can improve the wettability of the electrolyte and reduce the lithium-ion diffusion resistance. Polymer coating promotes the rapid diffusion of lithium ions and reduces concentration polarization by forming an artificial SEI film.

[0005] Although the existing modification technologies for fast charging graphite negative electrode materials have improved the performance of lithium-ion batteries to a certain extent, there are still many technical drawbacks and challenges. First, in terms of the modification of the bulk structure, although expanding the graphite layer spacing by methods such as oxidation, acidification, or etching can accelerate the diffusion of lithium ions, excessive expansion will cause microcracks in the negative electrode particles and the SEI film to break and reorganize, thereby consuming the electrolyte and reducing the cycle performance. Second, surface modification technologies such as carbon coating can improve the interfacial stability, but may increase the internal resistance of the battery, and improper selection of the coating layer will cause more side reactions. In addition, impurities introduced during the chemical modification process may cause additional side reactions and affect the charge and discharge rate. Under fast charging conditions, the graphite negative electrode also faces problems such as uneven lithium-ion deposition and lithium dendrite growth, which will not only reduce the battery capacity, but may also pose safety risks. At the same time, it is difficult for existing technologies to simultaneously meet the comprehensive requirements of lithium-ion batteries such as high specific capacity, high rate performance, and high cycle stability. Summary of the Invention

[0006] The present application provides a negative electrode material, a preparation method thereof and an application thereof, aiming to solve the problems such as slow lithium ion diffusion rate, high interfacial resistance, resulting in energy loss, electrolyte decomposition and graphite structure damage during fast charging of existing lithium ion batteries. At the same time, the cycle stability and safety of the battery are improved, and the bottleneck of traditional graphite negative electrodes in fast charging and long-life performance is broken through.

[0007] In the first aspect of the present application, a negative electrode material is provided, including graphite, non-metallic ions injected into the graphite by an ion implantation method, and a TiO2 coating layer coating the graphite.

[0008] According to some embodiments of the negative electrode material of the present application, it includes graphite, non-metallic ions injected into the graphite by an ion implantation method, and a TiO2 coating layer coating the graphite.

[0009] According to some embodiments of the negative electrode material of the present application, the injection amount of non-metallic ions in the negative electrode material is 1×10 15 -3×10 15 ions / cm 2 , preferably 1.8×10 15 -2.2×10 15 ions / cm 2 .

[0010] According to some embodiments of the negative electrode material of the present application, the non-metallic ions include B + , P 3- or N + , preferably B + .

[0011] According to some embodiments of the negative electrode material of the present application, the coating amount of TiO2 in the negative electrode material is 1.0-2.0 wt% of the graphite, preferably 1.5 wt%.

[0012] According to some embodiments of the negative electrode material of the present application, the particle size of the graphite is 10-20 μm.

[0013] In the second aspect of the present application, a preparation method of the negative electrode material described in the first aspect of the present application is provided, including the following steps:

[0014] (1) Inject non-metallic ions into the graphite by an ion implantation method, and then perform annealing treatment to obtain graphite containing non-metallic ions inside;

[0015] (2) Mix the graphite containing non-metallic ions inside with an aqueous TiO2 solution to obtain a mixture, perform solid-liquid separation treatment on the mixture, and sequentially perform drying and calcination treatment on the separated solid to obtain the negative electrode material.

[0016] In some embodiments of the method for preparing the negative electrode material according to the present application, in step (1), during the ion implantation process, the implantation energy is 30 - 50 keV, preferably 38 - 42 keV.

[0017] In some embodiments of the method for preparing the negative electrode material according to the present application, the non - metallic ions are implanted under vacuum conditions. Preferably, the non - metallic ions are implanted under the condition that the vacuum degree is 0.8×10 -6 - 1.0×10 -6 Torr.

[0018] In some embodiments of the method for preparing the negative electrode material according to the present application, in step (1), the annealing treatment is carried out in an inert atmosphere.

[0019] In some embodiments of the method for preparing the negative electrode material according to the present application, the annealing temperature is 800 - 1000 °C, and the annealing time is 1 - 2 h.

[0020] In some embodiments of the method for preparing the negative electrode material according to the present application, in step (2), the mass ratio of the graphite and TiO2 containing non - metallic ions inside is 1:(0.01 - 0.02), preferably 1:0.015.

[0021] In some embodiments of the method for preparing the negative electrode material according to the present application, the mass concentration of the TiO2 aqueous solution is 3 - 8 mg / ml.

[0022] In some embodiments of the method for preparing the negative electrode material according to the present application, the mixing temperature is 20 - 30 °C, the mixing rotation speed is 400 - 600 rpm, and the mixing time is 3 - 7 h.

[0023] In some embodiments of the method for preparing the negative electrode material according to the present application, the drying temperature is 80 - 100 °C, and the drying time is 10 - 14 h.

[0024] In some embodiments of the method for preparing the negative electrode material according to the present application, the drying is carried out in a vacuum environment.

[0025] In some embodiments of the method for preparing the negative electrode material according to the present application, the calcination temperature is 600 - 800 °C, and the calcination time is 3 - 5 h.

[0026] In some embodiments of the method for preparing the negative electrode material according to the present application, the calcination atmosphere is an inert atmosphere.

[0027] The third aspect of the present application provides a lithium - ion battery, including the negative electrode material described in the first aspect of the present application or the negative electrode material obtained by the preparation method described in the second aspect of the present application.

[0028] The beneficial effects of this application include: By means of ion implantation, the electronic structure of graphite is changed in the negative electrode material of this application, improving the diffusion rate of lithium ions and the electronic conductivity of the electrode, thereby significantly enhancing the fast charging performance of lithium-ion batteries; A TiO₂ coating is constructed on the graphite to form an artificial SEI layer, reducing the interfacial resistance, decreasing the energy loss during the desolvation process of lithium ions, and simultaneously suppressing the electrolyte decomposition and graphite exfoliation phenomena; In addition, the uniform distribution of TiO₂ nanoparticles can further improve the electrochemical performance and cycling stability of graphite.

[0029] In the negative electrode material of this application, the combination of ion implantation and surface coating is used to modify graphite, which not only optimizes the electron and ion transport efficiency inside graphite, but also enhances the interfacial stability through the surface coating, reducing side reactions, thereby achieving a comprehensive improvement in the high specific capacity, high rate performance, and long cycle life of lithium-ion batteries. Specific Embodiments

[0030] The embodiments of the present invention will be described in detail below. The examples of the embodiments are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0031] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc., mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0032] The negative electrode material provided by the embodiments of this application includes graphite, non-metallic ions implanted into the graphite by ion implantation method, and a TiO₂ coating layer covering the graphite.

[0033] The negative electrode material of this application combines ion implantation and surface coating to modify graphite, significantly enhancing the fast charging performance, cycling stability, and safety of the graphite negative electrode material, and is expected to become an important development direction for high-performance lithium-ion battery negative electrode materials.

[0034] In some embodiments of this application, the implantation amount of non-metallic ions in the negative electrode material is 1×10 15 -3×10 15 ions / cm 2 For example, 1×10 15ions / cm 2 、1.2×10 15 ions / cm 2 、1.5×10 15 ions / cm 2 、2×10 15 ions / cm 2 、2.5×10 15 ions / cm 2 、2.8×10 15 ions / cm 2 、3×10 15 ions / cm 2 By precisely controlling the injection dose, non-metal ion implantation can effectively improve the conductivity, interfacial kinetics, and structural stability of the graphite anode without sacrificing capacity.

[0035] In some embodiments of the present application, the implantation amount of non-metal ions in the anode material is 1.8×10 15 -2.2×10 15 ions / cm 2 .

[0036] In some embodiments of the present application, the non-metal ions include B + , P 3- or N + , where B + implantation can enhance electronic conductivity and stabilize the structure, inhibit side reactions, and extend the cycle life; P 3+ implantation can expand the layer spacing to accelerate lithium ion diffusion, improve the specific capacity and high voltage tolerance; N + implantation can improve the electron mobility, optimize the interfacial lithium ion transport, and stabilize the SEI layer to improve the fast charging performance.

[0037] In some embodiments of the present application, the non-metal ion is B + .

[0038] In some embodiments of the present application, the coating amount of TiO2 in the anode material is 1.0 - 2.0 wt% of the graphite. A low coating amount has little impact on the energy density but limited protection effect, while a high coating amount significantly increases the material cost and may cause agglomeration. Therefore, selecting an appropriate coating balances interface protection, ion transport, and cost.

[0039] In some embodiments of the present application, the coating amount of TiO2 in the anode material is 1.5 wt% of the graphite.

[0040] In some embodiments of the present application, the particle size of the graphite is 10 - 20 μm, such as 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, etc.

[0041] The embodiment of the present application also provides a preparation method of the negative electrode material described in the first aspect of the present application, including the following steps:

[0042] (1) Inject non-metallic ions into the interior of graphite by ion implantation, and then perform annealing treatment to obtain graphite containing non-metallic ions inside;

[0043] (2) Mix the graphite containing non-metallic ions inside with an aqueous TiO2 solution to obtain a mixture, perform solid-liquid separation treatment on the mixture, and sequentially perform drying and calcination treatments on the separated solid to obtain the negative electrode material. The TiO2 nanoparticles are evenly adsorbed on the surface of the graphite (mixing with the aqueous solution avoids dry agglomeration), forming a dense and continuous coating layer. Then, during the calcination process, the non-metallic ions (B / N / P) and the graphite carbon skeleton are stably doped at the sites through high-temperature bonding, and at the same time, the TiO2 coating layer further anchors the ions to prevent loss during the deintercalation process.

[0044] In some embodiments of the present application, in step (1), during the ion implantation process, the implantation energy is 30 - 50 keV, such as 30 keV, 35 keV, 40 keV, 43 keV, 48 keV, 50 keV, etc. Low-energy implantation is likely to result in insufficient implantation depth, and high-energy implantation is likely to cause excessive damage. At the same time, the ion implantation energy needs to be coordinated with the dose to avoid excessive damage to the graphite structure.

[0045] In some embodiments of the present application, in step (1), during the ion implantation process, the implantation energy is 38 - 42 keV.

[0046] In some embodiments of the present application, the non-metallic ions are implanted under vacuum conditions.

[0047] In some embodiments of the present application, the non-metallic ions are implanted under the condition that the vacuum degree is 0.8×10 -6 -1.0×10 -6 Torr.

[0048] In some embodiments of the present application, in step (1), the annealing treatment is carried out in an inert atmosphere; such as nitrogen atmosphere, argon atmosphere, etc.

[0049] In some embodiments of the present application, the annealing temperature is 800 - 1000 °C, such as 800 °C, 900 °C, 950 °C, 980 °C, 1000 °C, etc., and the annealing time is 1 - 2 h, such as 1 h, 1.2 h, 1.5 h, 2 h, etc.

[0050] In some embodiments of the present application, in step (2), the mass ratio of the graphite containing non-metal ions and TiO2 therein is 1:(0.01 - 0.02); for example, 1:0.01, 1:0.012, 1:0.015, 1:0.018, 1:0.02, etc.

[0051] In some embodiments of the present application, the mass concentration of the TiO2 aqueous solution is 3 - 8 mg / ml; for example, 3 mg / ml, 4 mg / ml, 5 mg / ml, 6 mg / ml, 8 mg / ml, etc.

[0052] In some embodiments of the present application, the temperature of the mixing is 20 - 30 °C, for example, 20 °C, 25 °C, 30 °C, etc., the rotation speed of the mixing is 400 - 600 rpm, for example, 400 rpm, 450 rpm, 500 rpm, 560 rpm, 600 rpm, etc., and the time of the mixing is 3 - 7 h, for example, 3 h, 4 h, 5 h, 6 h, 7 h, etc.

[0053] In some embodiments of the present application, the temperature of the drying is 80 - 100 °C; for example, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, etc., and the time of the drying is 10 - 14 h; for example, 10 h, 11 h, 12 h, 13 h, 14 h, etc.

[0054] In some embodiments of the present application, the drying is carried out in a vacuum environment.

[0055] In some embodiments of the present application, the temperature of the calcination is 600 - 800 °C, for example, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, etc., and the time of the calcination is 3 - 5 h; for example, 3 h, 4 h, 5 h, etc.

[0056] In some embodiments of the present application, the atmosphere of the calcination is an inert atmosphere.

[0057] The embodiments of the present application further provide a lithium-ion battery, including the negative electrode material described in the first aspect of the present application or the negative electrode material obtained by the preparation method described in the second aspect of the present application.

[0058] The technical solution of the present application will be further described below in conjunction with specific embodiments.

[0059] Example 1

[0060] Under the condition of high vacuum (vacuum degree is 10 -6 Torr), 5 g of natural graphite with a particle size of 10 - 20 μm is subjected to B + ion implantation to avoid the introduction of impurities. The ion dose of the ion implantation is 2×10 15 ions / cm 2, the energy of ion implantation is 40 keV. After the implantation is completed, the sample is annealed under nitrogen protection at a temperature of 900 °C for 1.5 hours.

[0061] 75 mg of TiO2 nanoparticles are ultrasonically dispersed in 15 ml of water to obtain a TiO2 dispersion with a mass concentration of 5 mg / ml. Subsequently, the graphite treated by B + ion implantation is added to the TiO2 dispersion, and the mixture is stirred at a speed of 500 rpm at room temperature of 25 °C for 5 hours to ensure that the TiO2 nanoparticles are evenly covered on the surface of the graphite. After the stirring is completed, the mixed suspension is subjected to solid-liquid separation to obtain a solid product. Finally, the solid product is dried in a vacuum at a temperature of 90 °C for 12 hours, and then calcined in an inert atmosphere at a temperature of 700 °C for 4 hours to obtain the modified graphite anode material coated with TiO2 + by ion implantation.

[0062] Example 2

[0063] The difference between the preparation method of the anode material described in Example 2 and that in Example 1 is only that: the non-metal ion implanted during the preparation process of the anode material described in Example 2 is N + , and the remaining operations are the same as those in Example 1.

[0064] Example 3

[0065] The difference between the preparation method of the anode material described in Example 3 and that in Example 1 is only that: the non-metal ion implanted during the preparation process of the anode material described in Example 3 is P 3- , and the remaining operations are the same as those in Example 1.

[0066] Example 4

[0067] The difference between the preparation method of the anode material described in Example 4 and that in Example 1 is only that: the implantation amount of non-metal ions during the preparation process of the anode material described in Example 4 is 1×10 15 ions / cm 2 , and the remaining operations are the same as those in Example 1.

[0068] Example 5

[0069] The difference between the preparation method of the anode material described in Example 5 and that in Example 1 is only that: the implantation amount of non-metal ions during the preparation process of the anode material described in Example 5 is 1.8×10 15 ions / cm 2 , and the remaining operations are the same as those in Example 1.

[0070] Example 6

[0071] The preparation method of the negative electrode material described in Example 6 is different from that of Example 1 only in that: the injection amount of non-metallic ions during the preparation of the negative electrode material described in Example 6 is 3×10 15 ions / cm 2 , and the remaining operations are the same as those in Example 1.

[0072] Example 7

[0073] The preparation method of the negative electrode material described in Example 7 is different from that of Example 1 only in that: the coating amount of TiO2 during the preparation of the negative electrode material described in Example 7 is 1.0 wt% of the mass of graphite.

[0074] The specific operation steps include:

[0075] Under high vacuum (vacuum degree is 10 -6 Torr), 5 g of natural graphite with a particle size of 10 - 20 μm is subjected to B + ion implantation to avoid impurity introduction. The ion dose of ion implantation is 2×10 15 ions / cm 2 , and the energy of ion implantation is 40 keV. After the implantation is completed, the sample is annealed under nitrogen protection at a temperature of 900 °C for 1.5 hours.

[0076] 50 mg of TiO2 nanoparticles are ultrasonically dispersed in 15 ml of water to obtain a TiO2 dispersion with a mass concentration of 3.33 mg / ml. Subsequently, the graphite treated by B + ion implantation is added to the TiO2 dispersion, and stirred and mixed at a rotation speed of 500 rpm at room temperature of 25 °C for 5 hours to ensure that the TiO2 nanoparticles are evenly covered on the surface of the graphite. After the stirring is completed, the mixed suspension is subjected to solid-liquid separation to obtain a solid product. Finally, the solid product is dried in a vacuum at a temperature of 90 °C for 12 hours, and then calcined in an inert atmosphere at a temperature of 700 °C for 4 hours to obtain the modified graphite negative electrode material with TiO2 coating and B + ion implantation.

[0077] Example 8

[0078] The preparation method of the negative electrode material described in Example 8 is different from that of Example 1 only in that: the coating amount of TiO2 in the graphite and the TiO2 coating layer during the preparation of the negative electrode material described in Example 8 is 1.7 wt%.

[0079] The specific operation steps include:

[0080] Under high vacuum (vacuum degree is 10 -6 Torr), 5 g of natural graphite with a particle size of 10 - 20 μm is subjected to B +Ion implantation is carried out to avoid impurity introduction. The ion dose of the ion implantation is 2×10 15 ions / cm 2 , and the energy of the ion implantation is 40 keV. After the implantation is completed, the sample is annealed under nitrogen protection at a temperature of 900 °C for 1.5 hours.

[0081] 85 mg of TiO2 nanoparticles are ultrasonically dispersed in 15 ml of water to obtain a TiO2 dispersion with a mass concentration of 5.67 mg / ml. Subsequently, the graphite treated by B + ion implantation is added to the TiO2 dispersion, and the mixture is stirred at a speed of 500 rpm at room temperature of 25 °C for 5 hours to ensure that the TiO2 nanoparticles are uniformly covered on the surface of the graphite. After the stirring is completed, the mixed suspension is subjected to solid-liquid separation to obtain a solid product. Finally, the solid product is dried in a vacuum at a temperature of 90 °C for 12 hours, and then calcined in an inert atmosphere at a temperature of 700 °C for 4 hours to obtain the modified graphite anode material coated with TiO2 by B + ion implantation.

[0082] Example 9

[0083] The difference between the preparation method of the anode material described in Example 9 and that in Example 1 is only that: in the preparation process of the anode material described in Example 9, the TiO2 coating amount in the graphite and the TiO2 coating layer is 2.0 wt%.

[0084] The specific operation steps include:

[0085] Under high vacuum (vacuum degree of 10 -6 Torr), 5 g of natural graphite with a particle size of 10-20 μm is subjected to B + ion implantation to avoid impurity introduction. The ion dose of the ion implantation is 2×10 15 ions / cm 2 , and the energy of the ion implantation is 40 keV. After the implantation is completed, the sample is annealed under nitrogen protection at a temperature of 900 °C for 1.5 hours.

[0086] 100 mg of TiO2 nanoparticles are ultrasonically dispersed in 15 ml of water to obtain a TiO2 dispersion with a mass concentration of 6.67 mg / ml. Subsequently, the graphite treated by B +Graphite treated by ion implantation was added to the TiO2 dispersion and stirred and mixed at a speed of 500 rpm at room temperature (25 °C) for 5 hours to ensure that the TiO2 nanoparticles uniformly covered the surface of the graphite. After stirring, the mixed suspension was subjected to solid-liquid separation to obtain a solid product. Finally, the solid product was dried in a vacuum at a temperature of 90 °C for 12 hours and then calcined in an inert atmosphere at a temperature of 700 °C for 4 hours to obtain TiO2-coated B + Modified graphite anode material by ion implantation.

[0087] Example 10

[0088] The preparation method of the anode material described in Example 10 is different from that of Example 1 only in that: during the preparation of the anode material described in Example 10, the ion implantation energy is 30 keV.

[0089] Example 11

[0090] The preparation method of the anode material described in Example 11 is different from that of Example 1 only in that: during the preparation of the anode material described in Example 11, the ion implantation energy is 38 keV.

[0091] Example 12

[0092] The preparation method of the anode material described in Example 12 is different from that of Example 1 only in that: during the preparation of the anode material described in Example 12, the ion implantation energy is 50 keV.

[0093] Comparative Example 1

[0094] The preparation method of the anode material described in Comparative Example 1 is different from that of Example 1 only in that: during the preparation of the anode material described in Comparative Example 1, the coating layer for coating the graphite is a SnO2 coating layer.

[0095] The specific operation steps include:

[0096] Under high vacuum (vacuum degree of 10 -6 Torr), 5 g of natural graphite with a particle size of 10 - 20 μm was subjected to B + ion implantation to avoid impurity introduction. The ion dose of the ion implantation is 2×10 15 ions / cm 2 , and the ion implantation energy is 40 keV. After the implantation, the sample was annealed under nitrogen protection at a temperature of 900 °C for 1.5 hours.

[0097] 75 mg of SnO2 nanoparticles were ultrasonically dispersed in 15 ml of water to obtain a SnO2 dispersion with a mass concentration of 5 mg / ml. Subsequently, after B +Graphite treated by ion implantation was added to the SnO2 dispersion liquid and stirred and mixed at a rotation speed of 500 rpm for 5 hours at room temperature of 25 °C to ensure that the SnO2 nanoparticles uniformly covered the graphite surface. After the stirring was completed, the mixed suspension was subjected to solid-liquid separation to obtain a solid product. Finally, the solid product was dried in a vacuum at a temperature of 90 °C for 12 hours, and then calcined in an inert atmosphere at a temperature of 700 °C for 4 hours to obtain SnO2-coated B + Modified graphite anode material by ion implantation.

[0098] Comparative Example 2

[0099] The difference between the preparation method of the anode material described in Comparative Example 2 and that of Example 1 is only that: during the preparation of the anode material described in Comparative Example 2, the graphite was not coated.

[0100] The specific operation steps include:

[0101] Under high vacuum (vacuum degree of 10 -6 Torr), 5 g of natural graphite with a particle size of 10-20 μm was subjected to B + ion implantation to avoid impurity introduction. The ion dose of the ion implantation was 2×10 15 ions / cm 2 , and the energy of the ion implantation was 40 keV. After the implantation was completed, the sample was annealed under nitrogen protection at a temperature of 900 °C for 1.5 hours to obtain the anode material.

[0102] Electrochemical performance study of the anode materials described in Examples 1-12 and Comparative Examples 1-2 of the present application

[0103] A CR 2016 coin-type battery was used, and 1M LiPF6 EC:DMC:DEC (1:1:1) was used as the electrolyte. A mixture of (anode active material (the anode active materials were the anode materials described in Examples 1-12 and Comparative Examples 1-2): polyvinylidene fluoride: conductive carbon black) with a mass ratio of 80:10:10 was dissolved in N-methylpyrrolidone (NMP) to obtain a uniform slurry. The slurry was uniformly coated on a copper foil to obtain an electrode sheet. After drying, the electrode sheet was cut into a disk with a diameter of 14 mm, and the load density of the disk was about 1.2 mg / cm 2 . A NEWARE BTS-5V battery test system was used to perform a constant current charge-discharge test on the half-cell, with a voltage range of 0.01-3V and an ambient temperature of 25±5 °C.

[0104] Evaluating the rate performance of the electrode sheet: Charge-discharge tests were carried out for 10 cycles at different rates of 0.1C, 0.2C, 0.5C, 1C, and 2C. Taking the initial discharge capacity at the 0.2C rate as the reference capacity, calculate the ratio of the discharge capacity of the 10th cycle at the 2C rate to the initial capacity, that is, the capacity retention rate (%) = (discharge capacity of the 10th cycle at 2C / initial capacity at 0.2C) × 100%. Through this index, the performance of the electrode sheet under high-rate charge-discharge conditions can be intuitively reflected: If the capacity retention rate at 2C is high, it indicates that the electrode sheet has good rate performance and kinetic stability; otherwise, it indicates that there may be kinetic bottlenecks or insufficient structural stability in the electrode material at high rates.

[0105] Evaluating the cycle performance of the electrode sheet: Constant current charge-discharge cycle tests were carried out at a rate of 0.5C. First, charge-discharge cycles were carried out for the first 3 cycles at a rate of 0.5C, and the discharge capacity of the 3rd cycle was taken as the initial capacity (if the capacity of the 3rd cycle is less than 1% of the 2nd cycle, the capacity of the 2nd cycle shall be used as the standard). Subsequently, continuous 500-cycle tests were carried out starting from the 4th cycle, and the discharge capacity of each cycle was recorded. Finally, calculate the ratio of the discharge capacity of the 500th cycle to the initial capacity, that is, the capacity retention rate (%) = (discharge capacity of the 500th cycle / initial capacity) × 100%. According to the level of the capacity retention rate, the performance of the electrode sheet during long-term cycling can be judged: If the capacity retention rate exceeds 80%, it indicates that the electrode sheet has good cycle stability and structural stability; if it is low, the material or battery design needs to be further optimized.

[0106] The test results are shown in Table 1.

[0107] Table 1

[0108] Capacity retention rate at 2C / 0.2C Capacity retention rate after 500 cycles at 0.5C Example 1 78.65％ 91.73％ Example 2 77.24％ 90.95％ Example 3 78.52％ 90.05％ Example 4 77.65％ 91.37％ Example 5 78.50％ 91.52％ Example 6 78.05％ 90.55％ Example 7 77.05％ 91.06％ Example 8 78.30％ 91.45％ Example 9 77.54％ 90.88％ Example 10 78.06％ 90.95％ Example 11 78.45％ 91.33％ Example 12 77.55％ 88.75％ Comparative Example 1 65.54％ 70.50％ Comparative Example 2 52.60％ 65.60％

[0109] From the comparative experimental data in Table 1, it can be seen that the graphite anode material modified by ion implantation and TiO2 surface coating in combination in the present invention shows significant performance advantages in lithium-ion batteries: the 2C / 0.2C capacity retention rate under high-rate charging reaches 78.65%, which is significantly improved compared with the single ion implantation (52.6%) or pure SnO2 coating (65.54%) scheme; the capacity retention rate after 500 cycles > 90%, which is also significantly improved compared with the single ion implantation (65.60%) or pure SnO2 coating (70.5%) scheme. This is because + the p-type doping effect introduced by B injection improves the electronic conductivity, and the nano-pores of the TiO2 coating layer provide fast ion transport channels. The two cooperate to break through the bottleneck that it is difficult to balance the bulk-phase and interface properties in traditional modification technologies, providing an ideal anode solution for high-power power batteries and long-life energy storage systems.

[0110] Although the above embodiments have been shown and described, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions, and variations made by those of ordinary skill in the art to the above embodiments are within the scope of protection of the present invention.

Claims

1. A negative electrode material, characterized in that: The invention comprises graphite, non-metallic ions implanted into the graphite by ion implantation and a TiO2 coating layer coating the graphite.

2. The negative electrode material according to claim 1, characterized in that The amount of non-metal ions injected into the negative electrode material is 1×10 15 -3×10 15 ions / cm 2 , preferably 1.8×10 15 -2.2×10 15 ions / cm 2 ; And / or, the non-metal ions include B + , P 3- or N + , preferably B + .

3. The negative electrode material according to claim 1, characterized in that The coating amount of TiO2 in the negative electrode material is 1.0-2.0wt% of the graphite, preferably 1.5wt%; And / or, the particle size of the graphite is 10-20 μm.

4. The method for preparing the negative electrode material according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) non-metallic ions are implanted into the interior of graphite by ion implantation, and then annealing is performed to obtain graphite containing non-metallic ions; (2) Graphite containing non-metallic ions is mixed with a TiO2 aqueous solution to obtain a mixture, the mixture is subjected to solid-liquid separation, and the separated solid is dried and calcined in sequence to obtain the negative electrode material.

5. The method for preparing the negative electrode material according to claim 4, characterized in that: In step (1), during the ion implantation process, the implantation energy is 30-50 keV, preferably 38-42 keV; And / or, the non-metallic ions are injected under vacuum conditions, preferably, the non-metallic ions are injected under a vacuum degree of 0.8×10 -6 -1.0×10 -6 Torr injection conditions.

6. The method for preparing the negative electrode material according to claim 4, characterized in that: In step (1), the annealing treatment is performed under an inert atmosphere; And / or, the annealing temperature is 800-1000° C., and the annealing time is 1-2 h.

7. The method for preparing the negative electrode material according to claim 4, characterized in that: In step (2), the mass ratio of the graphite containing non-metallic ions and TiO2 is 1:(0.01-0.02), preferably 1:0.015; And / or, the mass concentration of the TiO2 aqueous solution is 3-8 mg / ml; And / or, the mixing temperature is 20-30° C., the mixing speed is 400-600 rpm, and the mixing time is 3-7 h.

8. The method for preparing the negative electrode material according to claim 4, characterized in that: The drying temperature is 80-100°C and the drying time is 10-14h; And / or, the drying is drying under a vacuum environment.

9. The method for preparing the negative electrode material according to claim 4, characterized in that: The calcination temperature is 600-800°C, and the calcination time is 3-5h; And / or, the calcination atmosphere is an inert atmosphere.

10. A lithium ion battery, characterized in that: The invention comprises the negative electrode material according to any one of claims 1 to 3 or the negative electrode material obtained by the preparation method according to any one of claims 4 to 9.