Negative electrode material, preparation method thereof and secondary battery

Abstract

The invention provides a negative electrode material and a preparation method thereof, and a secondary battery, the provided negative electrode material comprises composite particles, and the composite particles comprise a tin-based material, phosphorus and a positive electrode material. By compounding the positive electrode material, on one hand, a certain lithium supplementing effect can be achieved, the first-circle coulombic efficiency of the battery is improved, and on the other hand, metal elements can be provided, the mechanical performance of the composite particles is improved, and the cycle performance of the battery is improved. According to the present invention, the negative electrode material is prepared into the negative electrode plate, and then the negative electrode plate is assembled into the battery for testing the electrochemical performance of the battery, and the experiment result shows that the battery prepared by the embodiment of the present invention has characteristics of high specific capacity, good cycle stability and practical application potential.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a negative electrode material, a preparation method thereof and a secondary battery. BACKGROUND

[0002] At present, tin-phosphorus-based negative electrode materials are suitable as battery negative electrode materials due to their lithium storage capacity far exceeding that of graphite, moderate lithium intercalation potential and abundant earth reserves.

[0003] However, the practical application of tin-phosphorus-based negative electrode materials still faces multiple technical challenges. Tin-phosphorus-based negative electrode materials have significant volume expansion during the cycling process, which causes the active particles to separate from the conductive agent, the SEI film to repeatedly break and regenerate, resulting in rapid capacity decay and low first coulombic efficiency, thereby affecting the battery performance and cycle life. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a negative electrode material, a preparation method thereof and a secondary battery, so as to solve the problem that the existing tin-phosphorus-based negative electrode material is prone to capacity decay due to volume expansion, low first coulombic efficiency, thereby affecting the cycle life of the battery.

[0005] In order to solve the above problems, the present application is realized by the following technical scheme:

[0006] The present application provides a negative electrode material, which comprises a composite particle, the composite particle comprising a tin-based material, phosphorus and a positive electrode material.

[0007] Further, a carbon film layer is arranged on the surface of the composite particle.

[0008] Further, the carbon film layer comprises expanded graphite.

[0009] Further, the negative electrode material comprises, by mass fraction: 65-88 parts of the tin-based material, 10-15 parts of phosphorus, 5-10 parts of the positive electrode material and 5-10 parts of the carbon film layer.

[0010] Further, the positive electrode material is selected from one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate and lithium vanadium phosphate, and / or the tin-based material is selected from one or more of tin powder, tin oxide and tin chloride.

[0011] Further, the negative electrode material has a median particle size of 6-7 microns.

[0012] The present application provides a preparation method of a negative electrode material, which comprises the following steps:

[0013] The tin-based material and the positive electrode material are subjected to ball milling treatment to obtain a first composite material;

[0014] adding a composite agent to the first composite material, the composite agent including phosphorus, and performing ball milling to form composite particles, to obtain the negative electrode material;

[0015] or, performing ball milling on the tin-based material, the positive electrode material, and a composite agent to form composite particles, to obtain the negative electrode material, the composite agent including phosphorus;

[0016] The ball milling is performed in an inert gas atmosphere.

[0017] Further, the composite agent further includes a carbon-based material, and the adding of the composite agent to the first composite material and the performing of the ball milling to form the composite particles to obtain the negative electrode material includes:

[0018] performing ball milling on the first composite material and phosphorus to obtain a second composite material;

[0019] performing ball milling on the second composite material and a carbon-based material to form composite particles, to obtain the negative electrode material;

[0020] or, the performing of the ball milling on the tin-based material, the positive electrode material, and a composite agent to form the composite particles to obtain the negative electrode material includes:

[0021] performing ball milling on the tin-based material, the positive electrode material, phosphorus, and a carbon-based material to form composite particles, to obtain the negative electrode material.

[0022] Further, the inert gas is argon and / or nitrogen.

[0023] The ball milling is performed in a ball milling tank, the ball milling tank being provided with milling balls, and a ball-to-material ratio being 25:1 to 50:1.

[0024] The ball milling is performed by high-energy ball milling or oscillation ball milling.

[0025] The ball milling is performed at a rotation speed of 900 rpm to 1200 rpm.

[0026] The ball milling is performed for 8 hours to 15 hours.

[0027] The application further provides a secondary battery including a negative electrode tab and a positive electrode tab, the negative electrode tab including a negative electrode current collector and a negative electrode material layer provided on the negative electrode current collector, the negative electrode material layer including the negative electrode material.

[0028] Compared with the prior art, the embodiments of the application have the following advantages:

[0029] In the embodiments of the present application, the provided negative electrode material comprises composite particles, the composite particles comprise a tin-based material, phosphorus and a positive electrode material. The positive electrode material is combined on one hand to play a certain lithium supplement role, to improve the first circle coulomb efficiency of the battery, and on the other hand to provide metal elements, to improve the mechanical properties of the composite particles and to improve the cycle performance of the battery.

[0030] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is the X-ray diffraction spectrum of the negative electrode material provided by the embodiments and the comparative examples of the present application;

[0032] Figure 2 is the scanning electron microscope image of the negative electrode material provided by the embodiments of the present application;

[0033] Figure 3 is the scanning electron microscope image of the negative electrode material provided by the comparative examples of the present application;

[0034] Figure 4 is the normal temperature charge-discharge curve of the lithium ion battery provided by the embodiments of the present application;

[0035] Figure 5 is the normal temperature charge-discharge cycle diagram of the lithium ion battery provided by the embodiments of the present application;

[0036] Figure 6 is the normal temperature charge-discharge curve of the lithium ion battery provided by the comparative examples of the present application;

[0037] Figure 7 is the normal temperature charge-discharge cycle diagram of the lithium ion battery provided by the comparative examples of the present application;

[0038] Figure 8 is the charge-discharge cycle diagram of the lithium ion battery provided by the embodiments 3 and the comparative example 1 of the present application at-10℃ low temperature;

[0039] Figure 9 is the charge-discharge cycle diagram of the lithium ion battery provided by the embodiments 3 of the present application at-30℃ low temperature. DETAILED DESCRIPTION

[0040] In order to make the technical problems, technical solutions and beneficial effects solved by the present application more clear and obvious, the present application will be further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and cannot limit the present application.

[0041] With the development of global energy transformation and high-end equipment technology, lithium-ion batteries have been widely used in grid energy storage, national defense equipment, space exploration, and deep-sea operations due to their high energy density and long cycle life. These applications require high energy density, low-temperature adaptability, and safety of the batteries. For example, in space environments, the battery must maintain stable charging and discharging below -40°C, and in deep-sea operations, the battery must provide continuous power under low temperature and high pressure. However, the graphite negative electrode material commonly used in current commercial lithium-ion batteries has a theoretical specific capacity of only 372 mAh / g based on the intercalation reaction of lithium ions between layers, and has significant defects in low-temperature environments. On the one hand, the lithium ion diffusion rate between graphite layers decreases exponentially with temperature, resulting in a capacity decay of over 40% at -20°C. On the other hand, the graphite lithium intercalation potential is close to that of metallic lithium, and the increased viscosity of the electrolyte at low temperatures exacerbates concentration polarization, which easily leads to lithium dendrite growth and short-circuit risk. Therefore, developing new negative electrode materials with high energy density and excellent low-temperature performance is a core direction for breaking through the application bottleneck of lithium-ion batteries in extreme conditions.

[0042] Tin-based negative electrode materials have become an ideal candidate to replace graphite due to their lithium storage capacity (theoretical specific capacity > 900 mAh / g) far exceeding that of graphite, moderate lithium intercalation potential, and abundant earth reserves. Their lithium storage mechanism is mainly based on alloying and conversion reactions, which are less affected by temperature than the intercalation mechanism of graphite, and can maintain more than 60% of the room temperature capacity at -30°C. The introduction of phosphorus further expands the performance advantages of tin-based materials: on the one hand, phosphorus (theoretical specific capacity 2596 mAh / g) can create a multi-active site structure for cooperative lithium storage through doping or forming tin-phosphorus compounds; on the other hand, Li3P generated by intercalating lithium has unique electrochemical properties, with an affinity energy (-0.72 eV) for lithium ions higher than that of traditional SEI components, and an ionic conductivity one order of magnitude higher than that of graphite SEI films, which can significantly reduce the desolvation energy barrier of lithium ions and promote low-temperature interfacial charge transfer. In addition, the tin-phosphorus composite system exhibits a "gradient expansion" characteristic during lithium extraction: the tin phase preferentially intercalates lithium and expands around 0.5 V, and the phosphorus phase stores lithium below 0.2 V, and the volume change of the two forms a mechanical buffer, which improves the cycle life of the material by more than 3 times (100-cycle capacity retention rate from 40% to 75%) compared to pure tin negative electrodes.

[0043] Although tin-phosphorus-based negative electrode materials exhibit excellent low-temperature lithium storage potential, their practical application still faces multiple technical challenges. First, the material has significant volume expansion (tin-based phase expansion rate of 300%, phosphorus-based phase expansion rate of more than 400%) during the cycle process, causing the active particles to separate from the conductive agent, the SEI film to repeatedly break and regenerate, and the problems of rapid capacity decay (capacity retention rate < 50% after 500 cycles) and low first coulombic efficiency (< 80%). Second, the crystal structure of tin-phosphorus compounds is prone to disordered transition during lithium ion deintercalation, resulting in unstable diffusion channels, especially in low-temperature environments below -20℃, the ion migration resistance is intensified, so that the material has a capacity of less than 60% at a rate of 0.1C. In addition, existing researches focus on the lithium storage mechanism at room temperature, and the researches on the evolution law of Li3P phase in low-temperature environment, the synergistic effect of tin-phosphorus interface and the dynamic growth mechanism of SEI film are still in blank, and there is a lack of effective strategies to optimize the low-temperature ion transmission path through structure design.

[0044] Based on the above problems, the negative electrode material provided in the embodiments of the present application includes a composite particle, and the composite particle includes a tin-based material, phosphorus and a positive electrode material.

[0045] In the embodiments of the present application, the negative electrode material includes a composite particle, and the composite particle includes a tin-based material, phosphorus and a positive electrode material. The positive electrode material can play a certain lithium supplementing role on one hand, improve the first coulombic efficiency of the battery, and on the other hand can provide metal elements to improve the mechanical properties of the composite particle and improve the cycle performance of the battery.

[0046] In the negative electrode material provided in the embodiments of the present application, the positive electrode material is selected from one or more of ternary materials, lithium cobaltate, lithium iron phosphate, lithium manganese iron phosphate and lithium vanadium phosphate. Optionally, in an embodiment, the positive electrode material is preferably ternary material and lithium iron phosphate. The ternary material includes lithium nickel cobalt manganese oxide (NCM) and lithium nickel cobalt aluminum oxide (NCA), wherein the performance balance is achieved by adjusting the nickel, cobalt and manganese ratio (such as NCM811), and the energy density advantage is significant. Lithium iron phosphate has high safety (decomposition temperature of 700℃), long cycle life (more than 3000 times) and low cost, which also has significant advantages. The tin-based material is selected from one or more of tin powder, tin oxide and tin chloride. Optionally, in an embodiment, the tin-based material is preferably tin powder.

[0047] In the embodiments of the present application, the negative electrode material comprises composite particles, the composite particles comprise a tin-based material, phosphorus and a positive electrode material. The positive electrode material is selected from one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, wherein the positive electrode material is combined on one hand to play a certain role of supplementing lithium to improve the first circle coulomb efficiency of the battery, and on the other hand to provide metal elements to improve the mechanical properties of the composite particles and improve the cycle performance of the battery. In addition, the transition metal oxide contained in the above-mentioned positive electrode material also plays a certain role of oxidizing tin and phosphorus to produce amorphous oxide, thereby improving the capacity of the negative electrode material.

[0048] Optionally, in an embodiment, the negative electrode material further comprises a carbon film layer, and the carbon film layer is arranged on the surface of the composite particles.

[0049] In the embodiments of the present application, the carbon film layer is arranged on the surface of the composite particles, that is, the carbon film layer coats the composite particles, which on one hand can prevent the direct contact of the electrolyte and the tin-based active substance, thereby preventing the continuous decomposition of the electrolyte and the growth of the surface film, and on the other hand can provide a buffer for the volume expansion of the tin-based active substance during the process of lithium extraction, thereby preventing the agglomeration and growth of the tin-based active substance particles.

[0050] Optionally, in an embodiment, the carbon film layer comprises expanded graphite.

[0051] It should be noted that the carbon film layer comprises expanded graphite, and the expanded graphite has a loose and porous vermicular structure, the interlayer spacing is significantly expanded, and the specific surface area is high. As a modified component of the negative electrode material, the expanded graphite can alleviate the volume expansion problem by optimizing the pore structure of the electrode, and can improve the cycle stability and low temperature performance of the battery by being combined with the tin-based high-capacity negative electrode material.

[0052] In the embodiments of the present application, the lithium extraction process of the tin-based material is regulated by phosphorus to accelerate the alloying reaction process with lithium, and the phosphorus also has a high specific capacity, which can improve the overall capacity of the negative electrode material. By using the positive electrode material as a negative electrode lithium supplementing agent and as a dopant of transition metal elements, the mechanical properties of the tin-phosphorus-based composite negative electrode material particles during the cycle process are improved, and the breakage of the composite particles is inhibited. By using expanded graphite as a carbon source, a good carbon coating effect is achieved by regulating the proportion of use, so that the electrode material maintains better cycle stability during the cycle process.

[0053] Optionally, in an embodiment, the negative electrode material comprises, in terms of mass parts, 65-88 parts of a tin-based material, 10-15 parts of phosphorus, 5-10 parts of a positive electrode material, and 5-10 parts of a carbon film layer.

[0054] For example, the tin-based material can be any value or a range value of any two of 65 parts, 68 parts, 70 parts, 73 parts, 75 parts, 78 parts, 80 parts, 83 parts, 85 parts, 88 parts. The phosphorus can be any value or a range value of any two of 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts. The positive electrode material can be any value or a range value of any two of 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts. The carbon film layer can be any value or a range value of any two of 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts.

[0055] It should be noted that the interlayer pores and three-dimensional network of the carbon film layer, especially the expanded graphite, can provide a fast diffusion channel for lithium ions. If the content of the carbon film layer is less than 5 parts, it cannot form a complete coating layer or a continuous conductive network, the electrode has poor conductivity, high internal resistance, and affects the rate performance and the response speed of lithium ions at low temperature; the stability of the SEI film is insufficient, the first coulombic efficiency is low, and the loss of active material is aggravated during the cycle process. If the content of the carbon film layer is more than 10 parts, it will increase the proportion of non-active substances, dilute the load of tin-phosphorus active substances, reduce the overall specific capacity of the electrode, and affect the energy density of the battery.

[0056] In the embodiments of the present application, by optimizing the ratio of tin-based material, phosphorus, positive electrode material and carbon film layer in the negative electrode material, the key indicators such as energy density, cycle stability, rate performance, low temperature adaptability and safety of the battery are balanced, the volume expansion, interface failure and low temperature performance bottleneck of the high-capacity negative electrode are solved, and the battery system design of "high energy density, long life and wide temperature range" is realized. Through the design of the coating structure and the precise control of the content of the carbon film layer, the key problems such as volume expansion, insufficient conductivity and unstable interface of the tin-phosphorus-based negative electrode material can be solved, and the low temperature performance can be improved through the unique porous characteristics of the expanded graphite, which promotes the development of tin-phosphorus-based materials in the direction of high cycle stability, high energy density and wide temperature range, making them more suitable for battery, energy storage system and special battery scenarios in extreme environments.

[0057] Optionally, in an embodiment, the median particle size of the negative electrode material is 6-7 microns.

[0058] In the embodiments of the present application, the median particle size, i.e. D50, of the negative electrode material is controlled to be 6-7 microns, which can be 6 microns, 6.5 microns or 7 microns. When the D50 is controlled to be 6-7 microns, the appropriate particle size can reduce the stress concentration inside the particles, reduce the risk of breakage, and at the same time control the specific surface area to reduce side reactions and prolong the cycle life.

[0059] The embodiments of the present application provide a preparation method of a negative electrode material, which comprises the following steps:

[0060] S1, ball milling the tin-based material and the positive electrode material to obtain a first composite material;

[0061] S2, adding a complexing agent to the first composite material and performing ball milling to form composite particles, so as to obtain the negative electrode material, wherein the complexing agent comprises phosphorus;

[0062] Or, tin-based material, positive electrode material and complexing agent are ball milled to form composite particles, so as to obtain the negative electrode material, wherein the complexing agent comprises phosphorus;

[0063] The ball milling is performed in an inert gas atmosphere.

[0064] It should be noted that the ball milling is performed in an inert gas atmosphere, and the inert gas comprises argon or / and nitrogen. The inert gas is used as a protective atmosphere in the ball milling process, and the main function is to solve the problems of material oxidation, moisture absorption, reaction out of control or safety risk in the ball milling process by creating an oxygen-free, dry and low-activity environment. The inert gas provides a double protection barrier of "physical isolation and chemical inertness" in the ball milling, so as to ensure that the high-activity materials (tin-based material, phosphorus and positive electrode material) remain pure in composition and stable in structure under the action of mechanical force.

[0065] In a specific implementation, S1, tin-based material and positive electrode material are weighed according to a certain mass ratio, mixed powder and grinding balls in a ball milling tank are filled in a ball milling tank in a ball milling tank, and the ball milling tank is sealed and ball milled in an inert gas atmosphere to obtain a first composite material; S2, the ball milling tank containing the first composite material is opened in an inert atmosphere, a certain mass ratio of complexing agent phosphorus is added, and the second ball milling is sealed to form composite particles, so as to obtain the negative electrode material.

[0066] The negative electrode lithium supplementing method on the market is mostly a method of directly calendering micron metal lithium onto a negative electrode sheet or a method of directly compounding negative electrode material with Li2O. These methods have certain safety hazards and industrial production difficulties, and the prepared negative electrode is easy to react and denature in air. The preparation method of the negative electrode material proposed in the embodiments of the present application adds positive electrode material to the negative electrode and fully ball mills and compounds, so as to improve the capacity of the tin-phosphorus-based negative electrode while improving the first circle coulomb efficiency of the battery, which is an ability that the traditional lithium supplementing agent does not have (the traditional lithium supplementing agent only reduces the lithium consumption of the first circle of the battery, but does not break through the theoretical capacity upper limit of the material system); in addition, the transition metal oxide part in the positive electrode material used in the embodiments of the present application may cause tin and phosphorus to be oxidized to form amorphous oxides, so as to improve the capacity, and the lithium contained in the positive electrode material reduces the consumption of lithium forming SEI film in the first circle.

[0067] Optionally, in an embodiment, the complexing agent further comprises a carbon-based material, and the adding of the complexing agent to the first composite material and the ball milling to form the composite particles so as to obtain the negative electrode material comprises:

[0068] S21a, ball-milling the first composite material with phosphorus to obtain a second composite material;

[0069] S22a, ball-milling the second composite material with a carbon-based material to form composite particles to obtain the negative electrode material;

[0070] Alternatively, the ball-milling the tin-based material, the positive electrode material, and the composite agent to form the composite particles to obtain the negative electrode material comprises:

[0071] ball-milling the tin-based material, the positive electrode material, phosphorus, and the carbon-based material to form the composite particles to obtain the negative electrode material.

[0072] It should be noted that if the tin-based material, the positive electrode material, phosphorus, and the carbon-based material are directly ball-milled together, the performance can also be obviously improved, but the carbon coating condition will be obviously deteriorated. Considering the performance and the carbon coating condition, the preparation method of adding the tin-based material, the positive electrode material, phosphorus, and the carbon-based material step by step for ball-milling to prepare the negative electrode material is preferred in the present application.

[0073] It should be noted that the carbon-based material is preferably expanded graphite, and the expanded graphite is combined with the tin-based high-capacity negative electrode material to improve the cycle stability and low-temperature performance of the battery.

[0074] It should be noted that the above steps S21a and S22a are carried out in an inert gas atmosphere, and the inert gas includes argon or / and nitrogen. The specific role of using the inert gas is consistent with the above steps S1 and S2, which will not be repeated here.

[0075] In the embodiments of the present application, when the tin-based material is tin powder, the particle size of the tin-based material is uniformly distributed at 50 nanometers. The particle size of tin has a regulating effect on the cycle performance of the battery, so the particle size of the tin-based material is controlled at about 50 nanometers. The phosphorus is selected from red phosphorus with a purity of 98.5%. When the carbon-based material is expanded graphite, the expanded graphite is 375 mesh. The size of the expanded graphite has an effect on successful carbon coating, and successful coating can prolong the cycle life in performance, therefore, the 375 mesh expanded graphite has better performance.

[0076] In specific implementation, the specific implementation process in steps S21a and S22a is similar to the above steps S1 and S2, which will not be repeated here.

[0077] Alternatively, in an embodiment, the inert gas is argon and / or nitrogen;

[0078] The ball-milling is carried out in a ball-milling tank, and the ball-milling tank is provided with grinding balls, and the ball-to-material ratio is 25-50:1,

[0079] and / or the ball milling treatment adopts high-energy ball milling or oscillation ball milling;

[0080] and / or the ball milling treatment rotation speed is 900-1200 rpm;

[0081] and / or the ball milling treatment time is 8-15 hours.

[0082] It should be noted that the ball milling method in the above steps is high-energy ball milling or oscillation ball milling, in order to ensure that the material is not contaminated, the ball milling bead material used is zirconia, and the zirconia ball milling beads used before and after the ball milling process need to be cleaned to eliminate the influence of surface impurities on the material.

[0083] The ball-to-material ratio is 25-50:1. For example, the ball-to-material ratio can be one of 25:1, 30:1, 35:1, 40:1, 45:1, 50:1 or a range value of any two thereof. By controlling the ball-to-material ratio to be 25-50:1, the interaction strength, frequency and efficiency of the grinding ball and the material can be adjusted to achieve precise regulation of the ball milling effect on the negative electrode material (such as particle size, morphology, dispersibility, reaction activity).

[0084] The ball milling rotation speed is 900-1200 rpm. For example, the rotation speed can be one of 900 rpm, 950 rpm, 1000 rpm, 1050 rpm, 1100 rpm, 1150 rpm, 1200 rpm or a range value of any two thereof. By controlling the ball milling rotation speed to be 900-1200 rpm, sufficient force (impact, friction, shear) can be provided to achieve crushing, mixing or reaction, so that defects (such as lattice distortion, dislocation) are generated on the surface of the composite particles, and even fresh surfaces are formed, promoting the interfacial reaction between different components.

[0085] The ball milling time is 8-15 hours, which can be any value of 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours or a range value of any two thereof, and is preferably 10 hours. A bidirectional intermittent operation mode is adopted, i.e. forward and reverse rotation is alternately operated, and the optional operation time is 5, 10, 15 or 20 minutes of operation and 5, 10, 15 or 20 minutes of pause. By controlling the ball milling time, on the one hand, the compounding degree of Sn and P and the size of Sn and P after compounding can be maintained at 5-10 microns, and on the other hand, the positive electrode material can be fully compounded with SnP.

[0086] In summary, the preparation method of the embodiments of the present application can achieve better compounding effect of tin and phosphorus through simple, controllable and step-by-step ball milling, and efficiently prepare a tin-phosphorus-based negative electrode material. The phosphorus in the tin-phosphorus-based negative electrode material regulates the de-lithiation process of the tin alloy, accelerates the alloying reaction process with lithium, and obtains a tin-phosphorus-based negative electrode material with higher specific capacity and better cycle performance, and also has good low-temperature performance, and has potential for large-scale production.

[0087] The embodiment of the present application further provides a secondary battery, comprising a negative electrode sheet and a positive electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode material layer arranged on the negative electrode current collector, the negative electrode material layer comprising the negative electrode material as described above.

[0088] The secondary battery provided by the embodiment of the present application further comprises a conductive agent and a binder; the binder can be sodium carboxymethyl cellulose and / or lithium polyacrylate; the conductive agent is composed of two conductive agents of Super C65 and single-walled carbon nanotubes, and the mass ratio of the two conductive agents is 50:1.

[0089] In some embodiments, the negative electrode sheet is prepared in the following manner: the negative electrode material, the binder and the conductive agent are uniformly mixed in a mass ratio of (7.5-8.5):(0.75-1.25):(0.75-1.25), and a negative electrode slurry is prepared by using deionized water as a solvent and through a high-speed stirring defoaming machine; the negative electrode slurry is coated on both sides of a negative electrode current collector such as a copper foil, and the coating thickness is 50-100 μm; and the prepared electrode sheet is subjected to processes of baking, rolling, cutting and the like, so that the negative electrode sheet is obtained.

[0090] The secondary battery provided by the embodiment of the present application further comprises a positive electrode sheet, a separator and an electrolyte.

[0091] The electrolyte can be in a liquid state, a gel state or a full solid state. In some embodiments, the electrolyte is prepared by dissolving 1 mol / L of lithium hexafluorophosphate in a mixed solvent of ethylene carbonate, methyl ethyl carbonate and propylene carbonate in a volume ratio of 1:1:1, and adding 10% of fluoroethylene carbonate by volume; and / or by dissolving 1 mol / L of lithium hexafluorophosphate in a mixed solvent of polycarbonate, dimethyl carbonate and methyl ethyl carbonate in a volume ratio of 1:1:1.

[0092] In actual application, in order to facilitate testing, the prepared negative electrode sheet can be punched into a round sheet with a diameter less than 20 mm, and then transferred to a glove box in a high-purity argon environment to assemble a CR20 series button cell, wherein lithium is used as a negative electrode sheet counter electrode in the button cell, and the water and oxygen contents in the glove box are both less than 0.01 ppm, so that the secondary battery is obtained.

[0093] The present application further provides a power-using device, comprising the secondary battery as described above, and the secondary battery is used as a power supply of the power-using device.

[0094] For the above-mentioned secondary battery embodiments and electrical equipment embodiments, their negative electrode plates include a negative electrode active material layer, and the above-mentioned negative electrode active material layer includes the above-mentioned negative electrode material, and can achieve the same technical effects. To avoid repetition, they will not be described here. For relevant details, please refer to the partial description of the negative electrode material embodiment.

[0095] In order to make the invention purpose, technical solution and beneficial effects of this application clearer, the present application is further described below in conjunction with examples. It should be understood that these examples are only used to illustrate this application and are not used to limit the scope of this application.

[0096] The present application is described in detail below through examples.

[0097] Test method:

[0098] The following tests were performed on the LAND CT2001A battery test system:

[0099] (1) Room temperature charge and discharge test

[0100] At room temperature (25°C), the charge and discharge current density was 200 mA / g, and the voltage range was 0.01 V to 1.5 V. The charge and discharge process was as follows: discharge at a current density of 200 mA / g to 0.01 V, let it rest for 3 minutes, then charge at a current density of 200 mA / g to 1.5 V, and record the discharge capacity.

[0101] The specific capacity is obtained by dividing the discharge capacity by the mass of the active material.

[0102] (2) Normal temperature cycle test

[0103] At room temperature (25°C), the charge and discharge current density is 1000mA / g, and the voltage range is 0.01V to 1.5V. The charge and discharge test is carried out at a current density of 1000mA / g for 150 cycles, and the discharge capacity of each cycle is recorded to characterize the cycle performance of the battery.

[0104] (3) Low temperature cycle test

[0105] At low temperature (the battery needs to be placed in a constant temperature box at -10℃ or -30℃ for testing), charge and discharge tests are carried out at a constant current density of 200mA / g. The test voltage range is 0.01V~1.5V, and the cycle is repeated 100 times. The discharge capacity of each cycle is recorded to characterize the cycle performance of the battery.

[0106] Capacity retention rate statistics:

[0107] The capacity retention rate was calculated based on the fourth discharge capacity.

[0108] Example 1

[0109] (1) Preparation of the negative electrode material:

[0110] S1, tin powder as a tin-based material, lithium nickel cobalt manganese oxide NCM811 powder as a positive electrode material, according to the mass ratio of 7:1, was added to the ball milling tank to form a mixed powder, and the ball milling tank was sealed with argon protection and then subjected to swing ball milling. The zirconium oxide grinding balls with a ball-to-material ratio of 30:1 were loaded into the ball milling tank. The working mode was set to "bidirectional intermittent operation, timed stop" mode, and the swing ball milling speed was 1000 rpm. After 10 min of forward operation, it was intermittently stopped for 10 min, then it was reversely operated for 10 min and then intermittently stopped for 10 min, which was taken as one cycle. The cycle was repeated for 30 times, and the total ball milling time was 10 h to obtain a first composite material.

[0111] S2, the ball milling tank containing the first composite material was opened under the atmosphere of argon protection, and 10 parts of red phosphorus as a composite agent were added. The ball milling tank was sealed and swing ball milling was continued, wherein the ball milling tank was loaded with zirconium oxide grinding balls with a ball-to-material ratio of 30:1. The working mode was set to "bidirectional intermittent operation, timed stop" mode, and the swing ball milling speed was 1000 rpm. After 10 min of forward operation, it was intermittently stopped for 10 min, then it was reversely operated for 10 min and then intermittently stopped for 10 min, which was taken as one cycle. The cycle was repeated for 15 times, and the total ball milling time was 5 h to form composite particles, so as to obtain a negative electrode material, which was named as 7-SPT8.

[0112] (2) Preparation of the negative electrode sheet:

[0113] The negative electrode material 7-SPT8 obtained by the above preparation method, a binder (sodium carboxymethyl cellulose CMC) and a conductive agent (Super C65 & single-walled carbon nanotube) were uniformly mixed according to the mass ratio of 8:1:1, and deionized water was used as a solvent. The negative electrode slurry was prepared by a high-speed stirring defoaming machine. The negative electrode slurry was uniformly coated on a battery-grade copper foil, and the coating thickness was controlled at 50-100 μm. After drying in a vacuum drying oven at 80°C for 12 hours to completely remove water, a 7-SPT8 negative electrode sheet was obtained by punching a round sheet less than 20 mm, wherein the active material loading was about 1.0-1.4 mg / cm 2 .

[0114] (3) Preparation of the lithium ion battery

[0115] Celgard2325 with a diameter of 19 mm was punched out as a separator film, and the separator film was dried in a vacuum oven at 80°C to remove residual moisture.

[0116] In an argon-filled glove box, the water and oxygen contents of which are controlled to be less than 0.01 ppm, the 7-SPT8 negative electrode sheet obtained in the above, the separator and the metal lithium counter electrode are sequentially assembled, and are fully infiltrated with an electrolyte, the electrolyte being 1 mol / L lithium hexafluorophosphate dissolved in a mixed solvent of ethylene carbonate, methyl ethyl carbonate and propylene carbonate in a volume ratio of 1:1:1, and 10% of fluoroethylene carbonate is added; a button-type CR2016 half battery is assembled to obtain a lithium ion battery.

[0117] Example 2

[0118] The difference between Example 2 and Example 1 is that:

[0119] In this example, the tin powder in step S1 is used as the tin-based material, and the lithium iron phosphate powder is used as the positive electrode material, which are added into the ball milling tank in a mass ratio of 5:1 to form a mixed powder.

[0120] Other steps and amounts are the same as in Example 1, and a button-type CR2016 half battery is obtained.

[0121] Example 3

[0122] The difference between Example 3 and Example 1 is that:

[0123] In this example, the mass ratio of the tin powder and the lithium nickel cobalt manganese oxide NCM811 powder in step S1 is adjusted to 5:1.

[0124] In the preparation process of the lithium ion battery, the electrolyte is adjusted to 1 mol / L lithium hexafluorophosphate dissolved in a mixed solvent of polycarbonate, dimethyl carbonate, methyl ethyl carbonate and fluoroethylene carbonate in a volume ratio of 3:3:3:1.

[0125] Other steps and amounts are the same as in Example 1, and a button-type CR2016 half battery is obtained.

[0126] Example 4

[0127] The difference between Example 4 and Example 1 is that:

[0128] In this example, the raw materials in step S1 are adjusted to be tin powder, red phosphorus powder and lithium iron phosphate powder, and the mass ratio is adjusted to be 7.5:1.5:1. The cycle is run for 15 times, and the total ball milling running time is 5h to obtain a first composite material.

[0129] In this example, step S2 is adjusted to add 10 parts of expanded graphite. The cycle is run for 9 times, and the total ball milling running time is 3h.

[0130] Other steps and amounts are the same as in Example 1, and a button-type CR2016 half battery is obtained.

[0131] Example 5

[0132] Example 5 differs from Example 1 in that:

[0133] In this example, the amount of tin powder and lithium nickel cobalt manganese oxide NCM811 powder added in step S1 is adjusted to 85 parts and 5 parts, respectively.

[0134] The other steps and amounts are the same as in Example 1, and a button CR2016 half battery is obtained.

[0135] Example 6

[0136] Example 6 differs from Example 4 in that:

[0137] In this example, the amount of expanded graphite added in step S2 is adjusted to 5 parts.

[0138] The other steps and amounts are the same as in Example 4, and a button CR2016 half battery is obtained.

[0139] Example 7

[0140] Example 7 differs from Example 4 in that:

[0141] In this example, the amount of expanded graphite added in step S2 is adjusted to 8 parts.

[0142] The other steps and amounts are the same as in Example 4, and a button CR2016 half battery is obtained.

[0143] Comparative Example 1

[0144] Comparative Example 1 differs from Example 1 in that:

[0145] In this comparative example, tin powder and phosphorus are used as raw materials, and are added to a ball mill tank in a mass ratio of 7:1 to form a mixed powder for first ball milling.

[0146] In this comparative example, the second ball milling in step S2 of Example 1 is not performed.

[0147] In the preparation process of the lithium ion battery, the electrolyte is adjusted to 1 mol / L lithium hexafluorophosphate dissolved in a mixed solvent of polycarbonate, dimethyl carbonate, methyl ethyl carbonate, and fluoroethylene carbonate in a volume ratio of 3:3:3:1.

[0148] The other steps and amounts are the same as in Example 1, and a button CR2016 half battery is obtained.

[0149] Comparative Example 2

[0150] Comparative Example 2 differs from Example 4 in that:

[0151] The comparative example adjusts the raw material in step S1 to tin powder, 2-5 μm range of nickel oxide, mass ratio 7:1, and does not add expanded graphite.

[0152] Other steps and amounts are the same as in Example 4, and a button CR2016 half cell is obtained.

[0153] Comparative Example 3

[0154] Comparative Example 3 differs from Example 4 in that:

[0155] The comparative example adjusts the raw material in step S1 to tin powder, and does not add phosphorus, positive electrode material, or expanded graphite.

[0156] Other steps and amounts are the same as in Example 4, and a button CR2016 half cell is obtained.

[0157] Comparative Example 4

[0158] Comparative Example 4 differs from Example 1 in that:

[0159] The comparative example does not add a positive electrode material or expanded graphite in step S1, and is otherwise identical to Example 1.

[0160] The negative electrode materials obtained in each example and comparative example are characterized, as shown in Figures 1-3 , to obtain the corresponding X-ray diffraction patterns (not including Comparative Example 3) and images under a scanning electron microscope.

[0161] The batteries obtained in each example and comparative example are tested for electrochemical performance, as shown in Figures 4-8 , to obtain the corresponding room temperature charge-discharge curves, room temperature charge-discharge cycle diagrams, and low-temperature charge-discharge cycle diagrams for each example and comparative example. The electrochemical performance test results for each example and comparative example are shown in Table 1.

[0162] Table 1

[0163]

[0164]

[0165] Figure 1 The X-ray diffraction patterns of the examples and comparative examples of the present application are known from Figure 1 , which shows that Examples 1-7 successfully synthesized the SnP alloy in Example 1, mainly Sn4P3, and there are some small peaks of lithium iron phosphate in Examples 2 and 4, mainly at 27, 35, 38, 51, and 53 degrees. Comparative Examples 1 and 3 hardly show the added ternary peaks, and the SnP peaks are also reduced, proving that the ball milling produced an amorphous oxide.

[0166] Figure 2is a scanning electron microscope image of the negative electrode material obtained by the embodiment of the present application; Figure 3 is a scanning electron microscope image of the negative electrode material obtained by the comparative example of the present application; from Figure 2 It can be observed that the spherical Sn has clear boundaries with each other after being compounded with P, Figure 2 It can be observed that the spherical Sn has clear boundaries with each other after being compounded with P, Figure 3 Compared with the comparative example, Figure 3 The particles in the embodiment 4 are obviously much larger under the same scale, and the micro-morphology of Sn cannot be better preserved, and Sn is more prone to agglomeration, resulting in a significant decrease in cycle performance.

[0167] As shown in Table 1, the test data of the first coulombic efficiency, the first discharge specific capacity, the discharge specific capacity after 150 cycles, and the capacity retention rate after 150 cycles of the batteries of the embodiments 1-7 are all greater than the test data in the comparative example, proving that the batteries obtained by the negative electrode material prepared by the embodiments of the present application have excellent electrochemical performance, that is, the negative electrode material obtained by the means of tin, phosphorus, positive electrode material compounding and carbon coating has a higher specific capacity and good cycle stability.

[0168] In the comparative example 2, no phosphorus is added, and the results show that the first coulombic efficiency, the first discharge specific capacity, the discharge specific capacity after 150 cycles, and the capacity retention rate after 150 cycles are all lower than those of the embodiments with phosphorus added. It can be seen that the capacity of the negative electrode material after compounding the positive electrode material is improved, but it still needs to be compounded with phosphorus to improve its basic cycle performance.

[0169] Figure 8 The charge-discharge cycle diagram of the lithium ion battery provided by the embodiment 3 at a low temperature of-10℃ is shown in FIG. 6, from Figure 8 As shown in FIG. 6, the battery prepared by the embodiment 3 has a first circle discharge specific capacity of 926 mAh / g at a low temperature, and after 100 cycles at-10℃, the discharge specific capacity is 721 mAh / g, and the capacity retention rate is 77.8%; at the same time, Figure 9 The charge-discharge cycle diagram of the lithium ion battery provided by the embodiment 3 at a low temperature of-30℃ is shown in FIG. 7, from Figure 9It can be seen that the discharge specific capacity is 553.52 mAh / g after 100 cycles at 200 mA / g at-30℃, and the reversible capacity retention rate is 70.9%. The battery prepared by the method of Comparative Example 1 has a first cycle discharge specific capacity of 572.3 mAh / g at low temperature, and the discharge specific capacity is 76.8 mAh / g after 100 cycles at-10℃, and the capacity retention rate is 13.4%. The test results show that the battery prepared by the negative electrode material of the application exhibits relatively high capacity and cycle stability at low temperature, which provides a material basis for realizing high energy density, high rate performance and high anti-low temperature lithium ion battery, and has certain enlightenment and help for breaking through the low temperature fast charging problem of lithium ion battery.

[0170] The negative electrode material prepared by the simple ball milling method in the application can effectively regulate the lithium extraction and insertion process of the tin alloy, accelerate the alloying reaction process with lithium, and has a high specific capacity, which can improve the overall capacity of the negative electrode. By using the positive electrode material as a negative electrode lithium supplement and a transition metal dopant, the mechanical properties of the negative electrode material particles during the cycle process are improved, and the particle breakage is inhibited. By using expanded graphite as a carbon source, a good coating effect is achieved by adjusting the proportion used, so that the electrode material has better cycle stability during the cycle process. The negative electrode material in the application is prepared by two-step ball milling, which can achieve better composite effect of tin and phosphorus. The experimental results show that the negative electrode material of the application has high specific capacity and stability during the charge and discharge cycle at room temperature or low temperature.

[0171] Although the preferred embodiments of the application have been described, those skilled in the art can make further changes and modifications to the embodiments once they know the basic inventive concept. Therefore, the claims are intended to include the preferred embodiments and all changes and modifications falling within the scope of the application.

[0172] The negative electrode material, the preparation method thereof, and the secondary battery provided by the application are described in detail above, and the principles and implementation modes of the application are described by applying specific examples; the above description of the embodiments is only used to help understand the method of the application and its core idea; at the same time, for those skilled in the art, according to the idea of the application, the specific implementation mode and application range can be changed; in view of the above, the content of the specification should not be understood as a limitation of the application.

Claims

1. A negative electrode material, characterized in that The invention comprises composite particles, wherein the composite particles comprise a tin-based material, phosphorus and a positive electrode material.

2. The negative electrode material according to claim 1, characterized in that It also includes a carbon film layer, which is arranged on the surface of the composite particles.

3. The negative electrode material according to claim 2, characterized in that The carbon film layer includes expanded graphite.

4. The negative electrode material according to claim 2, characterized in that Calculated by mass, the negative electrode material includes: 65 to 88 parts of tin-based material, 10 to 15 parts of phosphorus, 5 to 10 parts of positive electrode material, and 5 to 10 parts of carbon film layer.

5. The negative electrode material according to any one of claims 1 to 4, characterized in that The positive electrode material is selected from one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium vanadium phosphate; and / or the tin-based material is selected from one or more of tin powder, tin oxide, and tin chloride.

6. The negative electrode material according to claim 1, characterized in that The median particle size of the negative electrode material is 6 to 7 microns.

7. A method for preparing a negative electrode material, characterized in that: The preparation method comprises the following steps: ball milling the tin-based material and the positive electrode material to obtain a first composite material; adding a composite agent to the first composite material and then performing ball milling to form composite particles to obtain a negative electrode material, wherein the composite agent includes phosphorus; Alternatively, the tin-based material, the positive electrode material and the composite agent are ball-milled to form composite particles to obtain the negative electrode material, wherein the composite agent includes phosphorus; The ball milling process is performed under an inert gas atmosphere.

8. The preparation method according to claim 7, characterized in that The composite agent also includes a carbon-based material; The step of adding a composite agent to the first composite material and then performing ball milling to form composite particles to obtain a negative electrode material comprises: ball milling the first composite material with phosphorus to obtain a second composite material; ball milling the second composite material and the carbon-based material to form composite particles to obtain a negative electrode material; Alternatively, the step of ball milling the tin-based material, the positive electrode material and the composite agent to form composite particles to obtain the negative electrode material comprises: The tin-based material, the positive electrode material, the phosphorus and the carbon-based material are ball-milled to form composite particles to obtain the negative electrode material.

9. The preparation method according to any one of claims 7 to 8, characterized in that: The inert gas is argon and / or nitrogen; The ball milling process is carried out in a ball mill jar, which is filled with grinding balls, and the ball-to-material ratio is 25 to 50:1; And / or the ball milling treatment adopts high-energy ball milling or oscillating ball milling; and / or the ball milling speed is 900-1200 rpm; And / or the ball milling treatment time is 8 to 15 hours.

10. A secondary battery comprising a negative electrode sheet and a positive electrode sheet, characterized in that: The negative electrode plate includes a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector, and the negative electrode material layer includes the negative electrode material according to any one of claims 1 to 6.

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