Negative electrode material and preparation method therefor, and battery

Abstract

A negative electrode material and a preparation method therefor, and a battery. The negative electrode material comprises a silicon-based active material and lithium silicate; the negative electrode material further comprises the element Mg, the element Al and the element P, the mass content of the element Mg in the negative electrode material is a%, the mass content of the element Al in the negative electrode material is b%, the mass content of the element P in the negative electrode material is c%, and in the negative electrode material, a, b and c satisfy the following relational expressions: 0.3≤(a+b) / c≤1.5, and 0.5≤a+b+c≤10. The introduction of the elements Mg, Al and P into the negative electrode material can be beneficial to the formation of lithium ion transmission channels, which improves the rate performance of the negative electrode material.

Description

Negative electrode material and preparation method thereof, and battery

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on September 28, 2023, with application number 202311294348.1 and application name “Negative electrode material, preparation method thereof, and battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of negative electrode materials, and in particular to negative electrode materials, preparation methods thereof, and batteries. Background Art

[0003] As the application of lithium-ion batteries continues to expand and deepen, the requirements for lithium-ion battery performance are also increasing. In particular, in terms of battery energy density, traditional graphite anode materials are no longer sufficient to meet the growing market demand. As a high-capacity anode material, silicon oxide materials have attracted much attention in recent years. Silicon oxide materials have a specific capacity exceeding 2000mAh / g, but compared to graphite materials, silicon oxide materials have low first coulombic efficiency, poor conductivity, and inferior cycle and rate performance.

[0004] To improve the performance of silicon-oxygen materials, lithium doping is often used to increase their initial coulombic efficiency. However, lithium doping alters the silicon distribution within the original silicon-oxygen material, causing silicon aggregation and an increase in silicon grain size by over 50%, leading to degraded rate performance and decreased cycle performance. Furthermore, lithium-doped silicon-oxygen materials contain lithium silicates, which hydrolyze to produce high alkalinity. This degrades the polymer binder during aqueous slurry preparation, resulting in poor slurry stability and sedimentation, which can easily affect battery production.

[0005] Summary of the Invention

[0006] The embodiments of the present application provide a negative electrode material, a preparation method thereof, and a battery. By introducing Mg, Al, and P elements into the negative electrode material, it is beneficial to form a lithium ion transmission channel and improve the rate performance and cycle performance of the negative electrode material.

[0007] In a first aspect, an embodiment of the present application provides a negative electrode material, wherein the negative electrode material includes a silicon-based active material and a lithium silicate;

[0008] The negative electrode material also includes Mg, Al and P elements. The mass content of Mg in the negative electrode material is a%, the mass content of Al in the negative electrode material is b%, and the mass content of P in the negative electrode material is c%. In the negative electrode material, a, b and c satisfy the following relationship: 0.3≤(a+b) / c≤1.5, and 0.5≤a+b+c≤10.

[0009] In some embodiments, the silicon-based active material comprises silicon grains, and the size of the silicon grains is ≤20 nm.

[0010] In some embodiments, the silicon-based active material includes silicon and / or silicon oxide.

[0011] In some embodiments, the silicon-based active material includes silicon oxide, which is generally represented by the formula SiOx, wherein 0<x≤2.

[0012] In some embodiments, the lithium silicate includes at least one of Li2SiO3, Li2Si2O5, and Li4SiO4.

[0013] In some embodiments, in the negative electrode material, 0.002≤a / b≤2.

[0014] In some embodiments, the mass content of Mg element in the negative electrode material is a%, and 0.001≤a≤0.065.

[0015] In some embodiments, the mass content of Al element in the negative electrode material is b%, and 0.09≤b≤0.55.

[0016] In some embodiments, the mass content of the P element in the negative electrode material is c%, and 0.15≤c≤0.65.

[0017] In some embodiments, the negative electrode material further includes a carbon layer.

[0018] In some embodiments, the carbon layer includes at least one of an amorphous carbon material and a graphitized carbon material.

[0019] In some embodiments, the carbon layer includes an amorphous carbon material, and the amorphous carbon material includes at least one of amorphous carbon, carbon black, and activated carbon.

[0020] In some embodiments, the carbon layer includes a graphitized carbon material, and the graphitized carbon material includes at least one of conductive graphite and graphene.

[0021] In some embodiments, the particle size distribution of the negative electrode material satisfies: D10 ≥ 1.0 μm, 3 μm ≤ D50 ≤ 10 μm, and D90 ≤ 25.0 μm.

[0022] In some embodiments, the mass content of lithium silicate in the negative electrode material is 30% to 80%.

[0023] In some embodiments, the carbon layer has a thickness of 10 nm to 2000 nm.

[0024] In some embodiments, the mass percentage of carbon in the negative electrode material is 1% to 50%.

[0025] In some embodiments, the specific surface area of ​​the negative electrode material is 0.1 m 2 / g~50m 2 / g.

[0026] In some embodiments, the tap density of the negative electrode material is 0.5 g / cm 3 ~1.5g / cm 3 .

[0027] In some embodiments, the specific capacity of the negative electrode material is tested in the voltage range of 0 to 1.5 V, the specific capacity of the negative electrode material is A when the cut-off voltage is 0.3 V, the specific capacity of the negative electrode material is B when the cut-off voltage is 0.4 V, and the specific capacity of the negative electrode material is C when the cut-off voltage is 0.5 V, and the following relationship is satisfied: 0.7≤(CB) / (BA)≤1.3.

[0028] In some embodiments, the pH value of the negative electrode material is 9-12.

[0029] In a second aspect, the present application provides a method for preparing a negative electrode material, comprising the following steps:

[0030] The silicon-based raw material is immersed in a phosphoric acid solution for surface modification, and a precursor is obtained by solid-liquid separation;

[0031] A mixture comprising a precursor, a lithium source, a magnesium source and an aluminum source is heat-treated to obtain a negative electrode material, wherein the negative electrode material comprises a silicon-based active material and a lithium silicate, and further comprises Mg, Al and P elements, wherein the mass content of the Mg element in the negative electrode material is a%, the mass content of the Al element in the negative electrode material is b%, and the mass content of the P element in the negative electrode material is c%. In the negative electrode material, a, b and c satisfy the following relationship: 0.3≤(a+b) / c≤1.5, and 0.5≤a+b+c≤10.

[0032] In some embodiments, the silicon-based active material comprises silicon grains, and the size of the silicon grains is ≤20 nm.

[0033] In some embodiments, the silicon-based active material includes silicon and / or silicon oxide.

[0034] In some embodiments, the silicon-based active material includes silicon oxide SiOx, wherein 0<x≤2.

[0035] In some embodiments, the lithium silicate includes at least one of Li2SiO3, Li2Si2O5, and Li4SiO4.

[0036] In some embodiments, in the negative electrode material, 0.002≤a / b≤2.

[0037] In some embodiments, the concentration of the phosphoric acid solution is 0.05 mol / L to 5 mol / L.

[0038] In some embodiments, the immersion treatment time is 2 hours to 10 hours.

[0039] In some embodiments, the solid-liquid separation comprises at least one of filtration and centrifugation.

[0040] In some embodiments, the lithium source includes at least one of Li2O, Li2CO3, LiOH, Li, LiH, LiAlH4, and LiBH4.

[0041] In some embodiments, the magnesium source includes at least one of Mg2O, Mg, Mg(OH)2, and MgCl2.

[0042] In some embodiments, the aluminum source includes at least one of Al2O3, Al, Al(OH)3, and AlCl3.

[0043] In some embodiments, the heat treatment temperature is 400°C to 900°C.

[0044] In some embodiments, the heat treatment is carried out for a holding time of 2 hours to 12 hours.

[0045] In some embodiments, the heat treatment is performed in a protective atmosphere.

[0046] In some embodiments, the protective atmosphere gas includes at least one of nitrogen, helium, neon, argon, and krypton.

[0047] In some embodiments, before immersing the silicon-based raw material in a phosphoric acid solution for surface modification, the method further comprises: performing a carbon coating treatment on the silicon-based raw material to obtain a silicon-carbon composite, and using the silicon-carbon composite as the silicon-based raw material.

[0048] In some embodiments, after heat-treating the mixture comprising the precursor, the lithium source, the magnesium source, and the aluminum source, the method further comprises: carbon-coating the heat-treated product.

[0049] In some embodiments, the carbon coating process includes a vapor phase carbon coating process and / or a solid phase carbon coating process.

[0050] In a third aspect, the present application provides a battery, comprising the negative electrode material or the negative electrode material prepared by the method for preparing the negative electrode material.

[0051] The technical solution of this application has at least the following beneficial effects:

[0052] First, the negative electrode material provided by the present application introduces Mg, Al, and P elements into the negative electrode material. The Mg, Al, and P elements are coordinated with the O element in the silicon-based active material or the lithium silicate, which can be beneficial to the formation of lithium ion transmission channels, improve the rate performance of the negative electrode material, and control the range of (a+b) / c. The Mg, Al, P elements, the silicon-based active material and the lithium silicate can form faster and more lithium ion transmission channels, reduce the lithium ion transmission energy barrier, and improve the rate performance and cycle performance of the negative electrode material; and the introduction of Mg, Al, and P elements can reduce the hydrolysis of lithium silicate, thereby reducing the pH value of the negative electrode material and reducing the damage of the alkaline environment to the binder in the electrode sheet, which is beneficial to improving the processing stability problem of the pre-lithium negative electrode material. The slurry obtained by modulating the negative electrode material is more stable and not easy to settle or produce gas.

[0053] Secondly, the preparation method of the negative electrode material provided in the present application is as follows: the silicon-based raw material is immersed in a phosphoric acid solution so that phosphate ions are uniformly adhered to the surface of the silicon-based raw material, and then the silicon-based raw material with phosphate ions uniformly adhered to the surface is mixed with a lithium source, a magnesium source and an aluminum source and heat-treated. During the heat treatment process, the content ratio of Mg, Al and P elements is controlled, and then the range of (a+b) / c is controlled. The lithium source and the silicon-based active material form lithium silicate, and the lithium in part of the lithium silicate is replaced by magnesium and aluminum, and the silicon is replaced by phosphorus. Among them, Mg and Al elements have larger radii than Li, and phosphorus can also provide more bonding points than silicon. The combination of Mg, Al, P elements, silicon-based active materials and lithium silicate can form faster and more lithium ion transmission channels, thereby reducing the lithium ion transmission energy barrier.

[0054] The preparation method of the negative electrode material provided in this application can not only improve the electrochemical performance of the material, but also be suitable for large-scale production. The prepared negative electrode material can effectively improve the rate performance and cycle stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] FIG1 is a process flow chart of a method for preparing a negative electrode material provided in an embodiment of the present application;

[0056] FIG2 is a comparison of the cycle performance of the negative electrode materials prepared in Example 1 and Comparative Example 1 of the present application;

[0057] FIG3 is a schematic diagram of the cycle capacity retention state of the negative electrode material prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0058] The following are preferred implementations of the embodiments of the present application. It should be noted that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the embodiments of the present application. These improvements and modifications are also considered to be within the scope of protection of the embodiments of the present application.

[0059] As the application of lithium-ion batteries continues to expand and deepen, the requirements for lithium-ion battery performance are also increasing. In particular, in terms of battery energy density, traditional graphite anode materials are no longer sufficient to meet the growing market demand. As a high-capacity anode material, silicon oxide materials have attracted much attention in recent years. Silicon oxide materials have a specific capacity exceeding 2000mAh / g, but compared to graphite materials, silicon oxide materials have low first coulombic efficiency, poor conductivity, and inferior cycle and rate performance.

[0060] To improve the performance of silicon oxide materials, lithium doping is often used to increase their initial coulombic efficiency. However, lithium doping alters the distribution of silicon within the original silicon oxide material, causing silicon aggregation, leading to deterioration in the material's cycle and rate performance, and increased expansion. Furthermore, lithium-doped silicon oxide materials contain lithium silicates, which hydrolyze to produce high alkalinity. This degrades the polymer binder during aqueous slurry preparation, causing slurry sedimentation and potentially impacting battery fabrication.

[0061] Specifically, the present application provides a negative electrode material, the negative electrode material includes an active material, and the active material includes a silicon-based active material and lithium silicate;

[0062] The negative electrode material also includes Mg, Al and P elements. The mass content of Mg in the negative electrode material is a%, the mass content of Al in the negative electrode material is b%, and the mass content of P in the negative electrode material is c%, 0.3≤(a+b) / c≤1.5, and 0.5≤a+b+c≤10.

[0063] The negative electrode material provided by this application, after the introduction of Mg, Al, and P elements into the negative electrode material, the applicant speculates that the Mg, Al, and P elements coordinate with the O element in the silicon-based active material or lithium silicate, which can facilitate the formation of lithium ion transmission channels, improve the rate performance of the negative electrode material, control the range of (a+b) / c, and the Mg, Al, P elements, silicon-based active materials and lithium silicate can form faster and more lithium ion transmission channels, reducing the lithium ion transmission energy barrier; and the introduction of Mg, Al, and P elements can reduce the hydrolysis of lithium silicate, thereby reducing the pH value of the negative electrode material and reducing the damage of the alkaline environment to the binder in the electrode sheet, which is beneficial to improving the processing stability problem of the pre-lithium negative electrode material. The slurry prepared by the negative electrode material is more stable and not easy to settle or produce gas. After a large number of experiments, the applicant found that as long as the Mg, Al, and P elements are present and meet the regular relationship of 0.3≤(a+b) / c≤1.5 and 0.5≤a+b+c≤10, the expected technical effect can be achieved and the technical problem of this application can be solved.

[0064] In the above technical solution, (a+b) / c can specifically be 0.3, 0.5, 0.7, 0.8, 0.9, 1.0, 1.2, 1.3, 1.4 or 1.5, etc., and of course it can also be other values ​​within the above range, which are not limited here. When (a+b) / c<0.3, the amount of Mg and Al is too small, and the excess P combines with the Li pre-lithiation doped into the negative electrode material to form more lithium phosphate, resulting in the loss of active lithium ions and the reduction of the first efficiency of the negative electrode material. When (a+b) / c>1.5, the amount of P is too small, and the excess Mg and Al will combine excessively with Si and O to form magnesium silicate, aluminum silicate and other substances, causing silicon loss and a decrease in the specific capacity of the negative electrode material. Therefore, controlling the balance of the ratio of Mg, Al and P is conducive to forming an effective lithium ion transmission channel and improving the first coulombic efficiency and rate performance of the negative electrode material. Preferably, 0.6≤(a+b) / c≤1.2.

[0065] In the above technical solution, the value of a+b+c can specifically be 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, or 10, and of course, it can also be other values ​​within the above range, which is not limited here. If the value of a+b+c is too small, it means that the content of the doping element in the negative electrode material is too low, and insufficient magnesium aluminum phosphate-related substances are formed on the surface and / or within the silicon-based active material, resulting in a decrease in the pH value of the negative electrode material. After the negative electrode material is prepared to form a slurry, the slurry stability is reduced.

[0066] In some embodiments, the contents of Al, Mg, and P elements can be measured using an ICP method (Agilent 5800VDVICP-OES).

[0067] In some embodiments, the portion containing Al, Mg, and P elements, the applicant speculates, may include at least one of aluminosilicates, magnesium silicates, aluminophosphates, magnesium phosphates, magnesium oxide, aluminum oxide, phosphorus oxides, and phosphates, but is not limited thereto. Specifically, the portion containing Al, Mg, and P elements, the applicant speculates, may be at least one of LiAlSiO4, Al2SiO5, Al2O3, P2O5, Li3PO4, AlPO4, Al(PO3)3, LiAlO2, MgO, MgSiO3, Mg2SiO4, Mg3(PO4)2, and Li2Mg2O9Si3, but is not limited thereto. It should be noted that, given current detection technology, the applicant does not have a good way to fully confirm the specific existence form of Al, Mg, and P elements. However, from the discussion of the above principles, the data of the examples, and the analysis of the beneficial effects, the applicant can conclude that the technical problem of the present application can be solved when the content of Al, Mg, and P elements in the present application is controlled within the above range, and has no obvious relationship with the specific existence form of Al, Mg, and P elements.

[0068] In some embodiments, at least a portion of the Al element in the composite negative electrode material exists in a +3 valence form.

[0069] In some embodiments, the Mg element in the composite negative electrode material is at least partially present in a +2 valence form.

[0070] In some embodiments, the mass content of Mg element in the negative electrode material is a%, 0.001≤a≤0.065, specifically 0.001%, 0.004%, 0.006%, 0.008%, 0.01%, 0.03%, 0.035%, 0.038%, 0.040%, 0.041%, 0.045%, 0.05%, 0.055%, 0.065%, etc., which is not limited here.

[0071] In some embodiments, the mass content of Al element in the negative electrode material is b%, 0.09≤b≤0.55, specifically 0.09%, 0.095%, 0.1%, 0.12%, 0.15%, 0.2%, 0.25%, 0.35%, 0.39%, 0.40%, 0.42%, 0.50%, 0.55%, etc., which is not limited here.

[0072] In some embodiments, the mass content of the P element in the negative electrode material is c%, 0.15≤c≤0.70. Specifically, it can be 0.15%, 0.18%, 0.22%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6% or 0.65%, etc., which is not limited here.

[0073] In some embodiments, the silicon-based active material includes silicon grains, and the size of the silicon grains is ≤20 nm, specifically 20 nm, 19 nm, 18 nm, 15 nm, 12 nm, 10 nm, 8 nm, 5 nm or 2 nm, etc., which is not limited here.

[0074] In some embodiments, the silicon-based active material includes silicon and / or silicon oxide.

[0075] In some embodiments, the silicon-based active material comprises silicon oxide; silicon oxide can be represented by the general formula SiO x (0≤x≤2). In some interpretations, it can be a material formed by silicon particles dispersed in SiO2, or a material having a tetrahedral structural unit, with the silicon atom located at the center of the tetrahedral structural unit and the oxygen atoms located at the four vertices of the tetrahedral structural unit. Silicon oxide can specifically be SiO 0.2 、SiO 0.4 、SiO 0.6 、SiO 0.8 , SiO or SiO 1.2 etc. Preferably, the silicon oxide is SiO.

[0076] In some embodiments, the lithium silicate includes at least one of Li2SiO3, Li2Si2O5, and Li4SiO4. It is understood that the pre-lithiated silicon-based active material will produce a certain amount of lithium silicate, most of which is located on the surface and / or inside the silicon-based active material, or the silicon-based active material is dispersed in the lithium silicate.

[0077] In some embodiments, the mass content of Mg element in the negative electrode material is a%, the mass content of Al element in the negative electrode material is b%, and 0.002≤a / b≤2. Specifically, it can be 0.002, 0.005, 0.008, 0.01, 0.02, 0.03, 0.05, 0.1, 0.2, 0.3, 0.5, 0.8, 1, 1.5 or 2, etc., of course, it can also be other values ​​within the above range, which are not limited here. It can be understood that the atomic radius of Mg and Al is larger than that of Li. Mg and Al can occupy the lattice position of Li, which is conducive to the formation of larger ion channels, and the doping reaction activity of Mg is better, which can promote more uniform and effective doping of metal elements. Controlling the a / b ratio within the above range can make Mg 2+ With Al 3+ Balanced doping is achieved without causing a certain element to occupy too much of the Li lattice space. The formed magnesium aluminum phosphate and lithium silicate can also be more evenly dispersed on the surface and / or inside the silicon-based active material. Moreover, the simultaneous addition of Mg and Al can make the grains of the lithium silicate crystals more uniform, thereby improving the lithium ion transport performance.

[0078] In some embodiments, the negative electrode material further comprises a carbon layer. It is understood that the carbon layer is coated on at least a portion of the surface of the core containing the silicon-based active material and the lithium silicate.

[0079] In some embodiments, the thickness of the carbon layer is between 10 nm and 2000 nm; more specifically, it can be 10 nm, 50 nm, 100 nm, 300 nm, 500 nm, 800 nm, 1000 nm, 1500 nm, 1800 nm, or 2000 nm, without limitation. Controlling the thickness of the carbon layer helps improve lithium ion transmission efficiency, facilitates high-rate charge and discharge, reduces volume expansion, and enhances the cycling performance of the negative electrode material.

[0080] In some embodiments, the carbon layer includes at least one of an amorphous carbon material and a graphitized carbon material.

[0081] In some embodiments, the carbon layer includes an amorphous carbon material, and the amorphous carbon material includes at least one of amorphous carbon, carbon black, and activated carbon.

[0082] In some embodiments, the carbon layer includes a graphitized carbon material, and the graphitized carbon material includes at least one of conductive graphite and graphene.

[0083] In some embodiments, the tap density of the negative electrode material is 0.5 g / cm 3 ~1.5g / cm 3 , for example 0.2g / cm 3 , 0.3g / cm 3 , 0.5g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 1.0g / cm 3 , 1.2g / cm 3 etc. Preferably 0.7 g / cm 3 ~1.3g / cm 3 .

[0084] In some embodiments, the particle size distribution of the negative electrode material satisfies: 10 ≥1.0μm, 3μm≤D 50 ≤10μm, D 90 ≤25.0μm.

[0085] Specifically, the average particle size D of the negative electrode material 50 It can be 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, etc. The particle size D of the negative electrode material 10The particle size D of the negative electrode material can be 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 2.9 μm or 3 μm. 90 The particle size of the negative electrode material can be 25 μm, 20 μm, 18 μm, 15 μm, 12 μm or 10 μm, etc., and is not limited here. Controlling the particle size of the negative electrode material within the above range is beneficial to improving the cycle performance and rate performance of the negative electrode material.

[0086] In some embodiments, the specific surface area ratio of the negative electrode material is 0.1m 2 / g~50m 2 / g. Optionally, the specific surface area ratio of the composite negative electrode material can be 1m 2 / g、5m 2 / g、8m 2 / g、10m 2 / g、15m 2 / g, 20m 2 / g, 25m 2 / g、30m 2 / g、35m 2 / g, 40m 2 / g、45m 2 / g or 50m 2 / g, etc., which are not limited here; it can be understood that controlling the specific surface area within the above range is beneficial to reducing the consumption of irreversible active lithium ions and improving the first coulombic efficiency of the battery.

[0087] In some embodiments, the carbon content of the negative electrode material is 1% to 50% by weight. Specifically, it can be 1%, 5%, 8%, 10%, 15%, 20%, 30%, 35%, 40%, 45%, or 50%, etc., without limitation. It should be noted that the carbon in the negative electrode material originates from the carbon material in the carbon layer.

[0088] In some embodiments, the mass content of lithium silicate in the negative electrode material is 30% to 80%, and specifically can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 80%, etc., without limitation herein. Pre-lithiation of the silicon-based active material can effectively improve the initial coulombic efficiency of the negative electrode material.

[0089] In some embodiments, the lithium silicate is uniformly distributed on the surface and / or in the interior of the silicon-based active material, and at least a portion of the lithium silicate is located in the carbon layer.

[0090] In some embodiments, the specific capacity of the negative electrode material is tested in the voltage range of 0 to 1.5V. During the delithiation process of the negative electrode material, the specific capacity of the negative electrode material is A when the cut-off voltage is 0.3V, the specific capacity of the negative electrode material is B when the cut-off voltage is 0.4V, and the specific capacity of the negative electrode material is C when the cut-off voltage is 0.5V, and the following relationship is satisfied: 0.7≤(CB) / (BA)≤1.3; (CB) / (BA) can specifically be 0.7, 0.8, 0.9, 1.0, 1.1, 1.2 or 1.3, etc., and of course it can also be other values ​​within the above range. When (CB) / (BA) is lower than 0.7, there will be a certain loss in the capacity of the negative electrode material, and the first effect will be reduced. When (CB) / (BA) is greater than 1.3, there are more grains aggregated inside the negative electrode material, which affects the lithium ion transfer inside the negative electrode material and the cycle performance of the negative electrode material at room temperature deteriorates.

[0091] In some embodiments, the pH value of the negative electrode material is 9 to 12, specifically 9, 9.5, 10, 10.5, 11, 11.5, or 12, and other values ​​within the above range are also possible. The slurry prepared from the negative electrode material provided in this application is more stable and less prone to sedimentation and gas generation.

[0092] The present application also provides a method for preparing a composite negative electrode material, as shown in FIG1 , the method comprising the following steps S10 to S20:

[0093] S10, immersing the silicon-based raw material in a phosphoric acid solution for surface modification, and performing solid-liquid separation to obtain a precursor;

[0094] S20, heat-treating a mixture comprising a precursor, a lithium source, a magnesium source, and an aluminum source to obtain a negative electrode material, wherein the negative electrode material comprises a silicon-based active material and a lithium silicate, and the negative electrode material further comprises Mg, Al, and P. The mass content of the Mg element in the negative electrode material is a%, the mass content of the Al element in the negative electrode material is b%, and the mass content of the P element in the negative electrode material is c%. In the negative electrode material, a, b, and c satisfy the following relationship: 0.3≤(a+b) / c≤1.5, and 0.5≤a+b+c≤10.

[0095] The preparation method of the negative electrode material provided by this application involves immersing a silicon-based raw material in a phosphoric acid solution so that phosphate ions adhere uniformly to the surface of the silicon-based raw material. Then, the silicon-based raw material with uniformly adhered phosphate ions on its surface is mixed with a lithium source, a magnesium source, and an aluminum source and subjected to heat treatment. During the heat treatment process, a lithium silicate is formed between the lithium source and the silicon-based active material, and in some lithium silicates, lithium is replaced by magnesium and aluminum, and silicon is replaced by phosphorus. Among them, the Mg element and the Al element have a larger radius than Li, and phosphorus can also provide more bonding sites than silicon. The cooperation of the Mg, Al, P elements, the silicon-based active material, and the lithium silicate can form faster and more lithium ion transport channels, reducing the lithium ion transport energy barrier.

[0096] The following specifically introduces this solution:

[0097] S10, Immerse the silicon-based raw material in a phosphoric acid solution for surface modification treatment, and perform solid-liquid separation to obtain a precursor.

[0098] In some embodiments, the silicon-based raw material includes silicon oxide SiOy, where 0 < y ≤ 2; the silicon oxide can specifically be SiO 0.2 、SiO 0.4 、SiO 0.6 、SiO 0.8 、SiO or SiO 1.2 etc. Preferably, the silicon oxide is SiO.

[0099] In some embodiments, the concentration of the phosphoric acid solution is 0.05 mol / L to 5 mol / L, specifically it can be 0.05 mol / L, 0.1 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L or 5 mol / L, etc., which is not limited here.

[0100] In some embodiments, the impregnation treatment time is 2 h to 10 h; specifically it can be 2 h, 3 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, which is not limited here.

[0101] In some embodiments, the method of solid-liquid separation includes at least one of filtration and centrifugation. Filtration can be vacuum filtration, filter paper filtration, etc.

[0102] S20, Heat-treat the mixture containing the precursor, the lithium source, the magnesium source, and the aluminum source to obtain a negative electrode material. The negative electrode material includes a silicon-based active material and a lithium silicate. The negative electrode material also includes the Mg element, the Al element, and the P element. The mass content of the Mg element in the negative electrode material is a%, the mass content of the Al element in the negative electrode material is b%, and the mass content of the P element in the negative electrode material is c%. In the negative electrode material, a, b, and c satisfy the following relationship: 0.3 ≤ (a + b) / c ≤ 1.5, and 0.5 ≤ a + b + c ≤ 10.

[0103] In some embodiments, the silicon grains in the silicon-based active material are ≤ 20 nm, specifically, they can be 20 nm, 19 nm, 18 nm, 15 nm, 12 nm, 10 nm, 8 nm, 5 nm, 2 nm, etc., which are not limited herein.

[0104] In some embodiments, the silicon-based active material includes nano-silicon and / or silicon oxide.

[0105] In some embodiments, the silicon-based active material includes silicon oxide SiO x , where 0 < x ≤ 2; the silicon oxide can specifically be SiO 0.2 , SiO 0.4 , SiO 0.6 , SiO 0.8 , SiO or SiO 1.2 etc. Preferably, the silicon oxide is SiO.

[0106] In some embodiments, the lithium source includes at least one of Li2O, Li2CO3, LiOH, Li, LiH, LiAlH4, and LiBH4.

[0107] In some embodiments, the magnesium source includes at least one of Mg2O, Mg, Mg(OH)2, and MgCl2.

[0108] In some embodiments, the aluminum source includes at least one of Al2O3, Al, Al(OH)3, and AlCl3.

[0109] In some embodiments, the heat treatment temperature is 400 °C to 900 °C, and the heat treatment time is 2 h to 10 h; specifically, the heat treatment temperature can be 400 °C, 500 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, or 900 °C. The heat treatment time can specifically be 2 h, 4 h, 6 h, 8 h, 9 h, or 10 h, which are not limited herein.

[0110] In some embodiments, the heat treatment is carried out in a protective atmosphere;

[0111] In some embodiments, the gas in the protective atmosphere includes at least one of nitrogen, helium, neon, argon, and krypton.

[0112] In some embodiments, the lithium silicate includes at least one of Li2SiO3, Li2Si2O5, and Li4SiO4. It can be understood that the pre-lithiated silicon-based active material will generate a certain amount of lithium silicate, and most of these lithium silicates are located on the surface and / or inside of the silicon-based active material, or the silicon-based active material is dispersed in the lithium silicate.

[0113] In some embodiments, the mass content of Mg element in the negative electrode material is a%, the mass content of Al element in the negative electrode material is b%, and 0.002≤a / b≤2. Specifically, it can be 0.002, 0.005, 0.008, 0.01, 0.02, 0.03, 0.05, 0.1, 0.2, 0.3, 0.5, 0.8, 1, 1.5 or 2, etc., of course, it can also be other values ​​within the above range, which are not limited here. It can be understood that the atomic radius of Mg and Al is larger than that of Li. Mg and Al can occupy the lattice position of Li, which is conducive to the formation of larger ion channels, and the doping reaction activity of Mg is better, which can promote more uniform and effective doping of metal elements. Controlling the a / b ratio within the above range can make Mg 2+ With Al 3+ Balanced doping is achieved without causing a certain element to occupy too much of the Li lattice space. The formed magnesium aluminum phosphate and lithium silicate can also be more evenly dispersed on the surface and / or inside the silicon-based active material. Moreover, the simultaneous addition of Mg and Al can make the grains of the lithium silicate crystals more uniform, thereby improving the lithium ion transport performance.

[0114] In some embodiments, before S10 , the method further includes subjecting the silicon-based active material to a carbon coating process to obtain a silicon-carbon composite, and using the silicon-carbon composite as the silicon-based active material.

[0115] In some embodiments, after S20, the method further comprises subjecting the heat-treated product to a carbon coating treatment.

[0116] In some embodiments, the carbon coating process includes a vapor phase carbon coating process and / or a solid phase carbon coating process.

[0117] When the carbon coating process is a vapor-phase carbon coating process, it may specifically include: performing vapor-phase deposition on the silicon-based active material using a carbon source gas under a protective atmosphere to obtain a composite.

[0118] In some embodiments, the temperature of vapor deposition is 600° C. to 1000° C., and the temperature may be 600° C., 700° C., 800° C., 850° C., 900° C., 950° C., or 1000° C., etc., without limitation herein. Preferably, the temperature of vapor deposition is 700° C. to 900° C.

[0119] In some embodiments, the holding time of vapor deposition is 0.5 h to 10 h; the holding time can be 0.5 h, 1 h, 3 h, 6 h, 8 h, 9 h or 10 h, etc., which are not limited here. Preferably, the holding time of vapor deposition is 3 h to 9 h.

[0120] In some embodiments, the carbon source gas includes at least one of alkanes, cycloalkanes, alkenes, alkynes, and aromatic hydrocarbons. Specifically, the carbon source gas includes at least one of acetylene, methane, benzene, toluene, cyclohexane, ethanol, ethylene, and propylene.

[0121] In some embodiments, the concentration of the carbon source gas is 0.1 L / min to 10 L / min; specifically, it can be 0.1 L / min, 0.4 L / min, 0.6 L / min, 0.8 L / min, 1.0 L / min, 2 L / min, 5 L / min, 6 L / min, 8 L / min, 9 L / min, or 10 L / min, etc., without limitation herein. A certain concentration of carbon source gas is introduced as a source gas for the carbon material, and after a certain period of holding, the carbon material is deposited on the surface of the silicon-based active material.

[0122] When the carbon coating process is a solid-phase carbon coating process, it may specifically include: mixing the silicon-based raw material with the second carbon source, and performing a carbonization process to obtain a silicon-carbon composite.

[0123] In some embodiments, the second carbon source includes at least one of sucrose, glucose, polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenolic resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride and asphalt.

[0124] In some embodiments, the mass ratio of the silicon-based raw material to the second carbon source is (20-100): (10-80), and the mass ratio of the silicon-based active material to the second carbon source can be 20:10, 30:15, 50:60, 80:30, 90:20, 100:10, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0125] In some embodiments, the temperature of the carbonization treatment is 600° C. to 1000° C., and the temperature can specifically be 600° C., 700° C., 800° C., 810° C., 820° C., 830° C., 840° C., 850° C., 860° C., 870° C., 880° C., 890° C., 900° C., 950° C., or 1000° C., etc., without limitation herein. Preferably, the temperature of the carbonization treatment is 700° C. to 900° C.

[0126] In some embodiments, the holding time of the carbonization treatment is 0.5 h to 10 h, specifically 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, etc., which are not limited here. Preferably, the holding time of the carbonization treatment is 3 h to 5 h.

[0127] In some embodiments, the carbonization treatment is performed in a protective atmosphere, wherein the gas of the protective atmosphere comprises at least one of nitrogen, helium, neon, argon, and krypton.

[0128] In some embodiments, the silicon-carbon composite after carbon coating is further subjected to at least one of pulverization, screening, and demagnetization; preferably, the composite after carbon coating is further subjected to pulverization, screening, and demagnetization in sequence.

[0129] It should be noted that whether carbon coating is performed before step S10 or after step S20 has little impact on this case, as the carbon layer formed by coating does not affect the contact between the silicon-based raw material and phosphoric acid. Phosphoric acid can penetrate the carbon layer and evenly adhere to the surface of the silicon-based raw material. During the subsequent heat treatment, the lithium source and the silicon-based raw material form lithium silicate, and some of the lithium in the lithium silicate is replaced by magnesium and aluminum, and the silicon is replaced by phosphorus. Among them, divalent Mg and trivalent Al have larger radii than Li, and phosphorus can also provide more bonding points than silicon. When Mg, Al and P and O are coordinated, magnesium aluminum phosphate substances and lithium silicate are formed on the surface and / or inside the silicon-based active material. The lithium silicate and magnesium aluminum phosphate can form faster and more lithium ion transmission channels. In addition, the carbon coating treatment can further improve the volume expansion of the material and the efficiency of lithium ion transmission, which is conducive to high-rate charge and discharge of the material and improves the cycle performance of the negative electrode material.

[0130] The present application also provides a battery using the negative electrode material provided in the above embodiments of the present application or using the negative electrode material preparation method provided in the above embodiments of the present application. The battery provided in the present application has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion.

[0131] The following further illustrates the embodiments of the present application in multiple embodiments. The embodiments of the present application are not limited to the following specific embodiments. Within the scope of the unchanged main rights, appropriate changes can be made to the implementation.

[0132] Example 1

[0133] A method for preparing a negative electrode material comprises the following steps:

[0134] (1) Take 1kg SiO powder (D 50 =6.3 μm), placed in a tube furnace under nitrogen protection, heated to 900 ° C, introduced acetylene, kept warm for 3 hours and then cooled to obtain a carbon-coated SiO material;

[0135] (2) 100 g of phosphoric acid and 950 g of water were mixed to obtain a phosphoric acid solution, and the carbon-coated SiO material was immersed in the phosphoric acid solution for 6 h, and then filtered to obtain a precursor;

[0136] (3) Take 100g Li2O, 3g MgCl2, 30.3g AlCl3 and the precursor, mix them, then place them in a box furnace under nitrogen protection, heat them to 800℃, keep them warm for 4h, take them out and sieve them to obtain the negative electrode material.

[0137] The negative electrode material prepared in the embodiment of the present application includes an active material and a carbon layer located on at least a portion of the surface of the active material, and the active material includes a silicon-based active material and lithium silicate.

[0138] Other parameters of the negative electrode materials are detailed in Table 1.

[0139] Example 2

[0140] A method for preparing a negative electrode material comprises the following steps:

[0141] (1) Take 1kg SiO powder (D 50 =6.3 μm), placed in a tube furnace under nitrogen protection, heated to 900 ° C, introduced acetylene, kept warm for 3 hours and then cooled to obtain a carbon-coated SiO material;

[0142] (2) 100 g of phosphoric acid and 950 g of water were mixed to obtain a phosphoric acid solution, and the carbon-coated SiO material was immersed in the phosphoric acid solution for 6 h, and then filtered to obtain a precursor;

[0143] (3) Take 100g Li2O, 1.5g MgCl2, 21.5g AlCl3 and the precursor and mix them. Then place them in a box furnace under nitrogen protection, heat them to 800℃, keep them warm for 4h, take them out and sieve them to obtain the negative electrode material.

[0144] The negative electrode material prepared in the embodiment of the present application includes an active material and a carbon layer located on at least a portion of the surface of the active material, and the active material includes a silicon-based active material and lithium silicate.

[0145] Other parameters of the negative electrode materials are detailed in Table 1.

[0146] Example 3

[0147] A method for preparing a negative electrode material comprises the following steps:

[0148] (1) Take 1kg SiO powder (D 50 =6.3 μm), placed in a tube furnace under nitrogen protection, heated to 900 ° C, introduced acetylene, kept warm for 3 hours and then cooled to obtain a carbon-coated SiO material;

[0149] (2) 150 g of phosphoric acid and 950 g of water were mixed to obtain a phosphoric acid solution, and the carbon-coated SiO material was immersed in the phosphoric acid solution for 6 h, and then filtered to obtain a precursor;

[0150] (3) Take 100g Li2O, 1.5g MgCl2, 10.5g AlCl3 and the precursor, mix them, then place them in a box furnace under nitrogen protection, heat them to 800℃, keep them warm for 4h, take them out and sieve them to obtain the negative electrode material.

[0151] The negative electrode material prepared in the embodiment of the present application includes an active material and a carbon layer located on at least a portion of the surface of the active material, and the active material includes a silicon-based active material and lithium silicate.

[0152] Other parameters of the negative electrode materials are detailed in Table 1.

[0153] Example 4

[0154] A method for preparing a negative electrode material comprises the following steps:

[0155] (1) Take 1kg SiO powder (D 50 =6.3 μm), placed in a tube furnace under nitrogen protection, heated to 900 ° C, introduced acetylene, kept warm for 3 hours and then cooled to obtain a carbon-coated SiO material;

[0156] (2) 50 g of phosphoric acid and 950 g of water were mixed to obtain a phosphoric acid solution. The carbon-coated SiO material was immersed in the phosphoric acid solution for 6 h, and then filtered to obtain a precursor.

[0157] (3) Take 100g Li2O, 1.5g MgCl2, 18g AlCl3 and the precursor and mix them. Then place them in a box furnace under nitrogen protection, heat them to 800℃, keep them warm for 4h, take them out and sieve them to obtain the negative electrode material.

[0158] The negative electrode material prepared in the embodiment of the present application includes an active material and a carbon layer located on at least a portion of the surface of the active material, and the active material includes a silicon-based active material and lithium silicate.

[0159] Other parameters of the negative electrode materials are detailed in Table 1.

[0160] Example 5

[0161] A method for preparing a negative electrode material comprises the following steps:

[0162] (1) Take 1kg SiO powder (D 50 =6.3 μm), placed in a tube furnace under nitrogen protection, heated to 900 ° C, introduced acetylene, kept warm for 3 hours and then cooled to obtain a carbon-coated SiO material;

[0163] (2) 80 g of phosphoric acid and 950 g of water were mixed to obtain a phosphoric acid solution. The carbon-coated SiO material was immersed in the phosphoric acid solution for 6 h, and then filtered to obtain a precursor.

[0164] (3) Take 100g Li2O, 1g MgCl2, 5g AlCl3 and the precursor and mix them. Then place them in a box furnace under nitrogen protection, heat them to 800℃, keep them warm for 4h, take them out and sieve them to obtain the negative electrode material.

[0165] The negative electrode material prepared in the embodiment of the present application includes an active material and a carbon layer located on at least a portion of the surface of the active material, and the active material includes a silicon-based active material and lithium silicate.

[0166] Other parameters of the negative electrode materials are detailed in Table 1.

[0167] Example 6

[0168] (1) Take 100g of phosphoric acid and 950g of water and mix them evenly to obtain a phosphoric acid solution. 50 =6.3) soaked in phosphoric acid solution for 6 h, and then filtered to obtain a precursor;

[0169] (2) 100 g of Li2O, 3 g of MgCl2, 30.3 g of AlCl3 and the precursor were mixed, and then placed in a box furnace under nitrogen protection, heated to 800 ° C, kept warm for 4 h, and then taken out and sieved to obtain a mixture;

[0170] (3) 1.5 kg of the mixture and 120 g of asphalt were placed in a VC machine and mixed for 40 min at a speed of 500 rpm. After the material was discharged, it was placed in a high-temperature box furnace and calcined at 800 ° C for 6 h. Nitrogen was introduced into the box furnace for protection. The material was naturally cooled to room temperature and discharged to obtain the negative electrode material.

[0171] The negative electrode material prepared in the embodiment of the present application includes an active material and a carbon layer located on at least a portion of the surface of the active material, and the active material includes a silicon-based active material and lithium silicate.

[0172] Other parameters of the negative electrode materials are detailed in Table 1.

[0173] Example 7

[0174] The difference from Example 1 is that the silicon-based raw material in step (1) is SiO 0.8 .

[0175] Example 8

[0176] Different from Example 1,

[0177] (3) Take 100g Li2O, 1.3g MgO, 23.1g Al2O3 and the precursor and mix them. Then place them in a box furnace under nitrogen protection, heat them to 800℃, keep them warm for 4h, take them out and sieve them to obtain the negative electrode material.

[0178] Comparative Example 1

[0179] (1) Take 1kg SiO powder (D 50 =6.3 μm), placed in a tube furnace under nitrogen protection, heated to 900 ° C, introduced acetylene, kept warm for 3 hours and then cooled to obtain a carbon-coated SiO material;

[0180] (2) 100 g of Li2O and carbon-coated SiO material were mixed and then placed in a box furnace under nitrogen protection. The temperature was raised to 800 °C and kept at this temperature for 4 h. The mixture was taken out and sieved to obtain the negative electrode material.

[0181] Comparative Example 2

[0182] (1) 1 kg of SiO powder (D50 = 6.3 μm) was placed in a tube furnace and heated to 900 °C under nitrogen protection. Acetylene was introduced and kept at this temperature for 3 h before cooling to obtain a carbon-coated SiO material.

[0183] (2) 62.5 g of phosphoric acid and 950 g of water were mixed to obtain a phosphoric acid solution. The carbon-coated SiO material was immersed in the phosphoric acid solution for 6 h, and then filtered to obtain a precursor.

[0184] (3) Take 100g Li2O, 1g MgCl2, 17g AlCl3 and the precursor and mix them. Then place them in a box furnace under nitrogen protection, heat them to 800℃, keep them warm for 4h, take them out and sieve them to obtain the negative electrode material.

[0185] Comparative Example 3

[0186] (1) 1 kg of SiO powder (D50 = 6.3 μm) was placed in a tube furnace and heated to 900 °C under nitrogen protection. Acetylene was introduced and kept at this temperature for 3 h before cooling to obtain a carbon-coated SiO material.

[0187] (2) 150 g of phosphoric acid and 950 g of water were mixed to obtain a phosphoric acid solution, and the carbon-coated SiO material was immersed in the phosphoric acid solution for 6 h, and then filtered to obtain a precursor;

[0188] (3) Take 100g Li2O, 1.3g MgCl2, 7.5g AlCl3 and the precursor and mix them. Then place them in a box furnace under nitrogen protection, heat them to 800℃, keep them warm for 4h, take them out and sieve them to obtain the negative electrode material.

[0189] Test method:

[0190] (1) Particle size of negative electrode material:

[0191] Particle size is measured using Mastersizer 3000 laser diffraction technology. When a laser beam passes through a dispersed particle sample, the particle size measurement is completed by measuring the intensity of the scattered light. The data is then used to analyze and calculate the particle size distribution that forms the scattering spectrum. D50: The particle size corresponding to when the cumulative particle size distribution percentage of a sample reaches 50%. Its physical meaning is that 50% of the particles have a particle size larger than it, and 50% of the particles have a particle size smaller than it. D50 is also called the median diameter or median particle size. D90 particle size, D50 particle size, and D10 particle size are the equivalent diameters (average particle sizes) of the largest particles when the cumulative distribution in the distribution curve is 90%, 50%, and 10%, respectively.

[0192] (2) Test method for specific surface area of ​​negative electrode material:

[0193] At constant temperature and low temperature, after measuring the adsorption amount of gas on the solid surface at different relative pressures, the monolayer adsorption amount of the sample is obtained based on the Brownauer-Ettel-Taylor adsorption theory and its formula (BET formula), thereby calculating the specific surface area of ​​the material.

[0194] (3) Test method for tap density:

[0195] The tap density was tested by using a Quanta vibrator. A certain amount of sample was weighed and vibrated 3000 times at 300 times / min.

[0196] (4) XRD test:

[0197] Silicon microcrystal size test method:

[0198] The XRD peak was measured using a Panatech X'pert Pro X-ray diffractometer, and then the Si peak in the XRD was fitted and analyzed using Xpert High Score software to calculate the Si crystallite size.

[0199] Lithium silicate content test:

[0200] MgO was used as an internal standard to quantitatively analyze the lithium silicate content. XRD peaks were measured using a Panatech X'pert Pro X-ray diffractometer. Jade software was then used to subtract background, smooth, and find peaks. Fitting analysis was then performed, and the lithium silicate content was calculated by comparing the peaks with the MgO content.

[0201] (5) Carbon content test method:

[0202] The carbon content was tested by thermogravimetric analysis.

[0203] (6) Test of the mass content of Al, Mg and P in the negative electrode material:

[0204] The ICP method was used to test the Al, Mg, and P contents in the material. The test method: 0.500g of the negative electrode material was placed in a clean platinum crucible, then calcined at 750°C in an air atmosphere muffle furnace for 2 hours to completely remove the carbon element; the cooled calcined residue was fully reacted with a mixed acid of 4mL HNO3 and 6mL HF, and the platinum crucible containing the solution was then placed on a 350°C hot plate until the solvent completely evaporated; after the crucible cooled, 6mL HCl was added, heated until the residue was completely dissolved, and the volume was adjusted to a 100mL plastic volumetric flask; finally, an ICP spectrometer (Agilent 5800VDV ICP-OES) was used to test the total Al, Mg, and P contents of the material. It is understandable that 10,000ppm is equivalent to 1% by mass.

[0205] (7) Button battery test:

[0206] The negative electrode material, conductive carbon black, and binder (styrene-butadiene rubber and hydroxymethyl cellulose) were prepared into a slurry in a ratio of 75:15:10, evenly coated on copper foil and dried to form a negative electrode sheet, which was assembled into a button battery in an argon atmosphere glove box. The separator used was a polypropylene microporous membrane, the electrolyte used was 1 mol / L lithium hexafluorophosphate (the solvent was a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate), and the positive electrode sheet used was a metal lithium sheet.

[0207] The battery was tested using a BlueDian Xinwei 5V / 10mA battery tester with a voltage of 1.5V and a current of 0.1C. The first coulombic efficiency = first charge specific capacity / first discharge specific capacity.

[0208] (8) Cyclic performance test:

[0209] The negative electrode materials prepared in the above examples and comparative examples were mixed with graphite in a mass ratio of 15:85 to form a negative electrode material, and then respectively mixed with graphite in a mass ratio of 15:85 to obtain a negative electrode active material. The negative electrode active material, conductive carbon black, hydroxymethyl cellulose and styrene-butadiene rubber were then uniformly mixed in a mass ratio of 92:4:2:2, and coated on a copper foil to prepare a negative electrode sheet. A metal lithium sheet was used as a positive electrode sheet, and polyethylene was used as a separator to prepare a button battery.

[0210] Tested using a BlueDian Xinwei 5V / 10mA battery tester with a voltage of 1.5V and a current of 0.1C. 50-cycle cycle retention rate = 50th discharge specific capacity / first discharge specific capacity.

[0211] The battery was tested using a Blue Power 5V / 10mA battery tester with a voltage of 1.5V and currents of 0.1C and 3C respectively. 3C / 0.1C = discharge capacity at 3C current / discharge capacity at 0.1C current.

[0212] The specific capacity of the negative electrode material was tested in the voltage range of 0 to 1.5 V. When the cut-off voltage was 0.3 V, the specific capacity of the negative electrode material was A. When the cut-off voltage was 0.4 V, the specific capacity of the negative electrode material was B. When the cut-off voltage was 0.5 V, the specific capacity of the negative electrode material was C.

[0213] (9) Slurry stability test:

[0214] The negative electrode materials prepared in each embodiment and comparative example were used as active materials, and the negative electrode material, conductive carbon black, and binder (styrene-butadiene rubber and hydroxymethyl cellulose) were prepared into a slurry in a ratio of 75:15:10. The slurry was placed in an aluminum-plastic film bag, sealed, and allowed to stand. The shape changes of the aluminum-plastic film bag were then monitored for a monitoring period of 1 month.

[0215] (10) pH value test method

[0216] Use Mettler FE20 pH meter to test the pH value of the material. Calibrate it before use. The calibration method is as follows: remove the protective liquid sleeve on the electrode, rinse it with pure water several times, and soak it in distilled water for 30 minutes; take out the electrode, wipe the pH electrode dry with a paper towel or filter paper, then pour 4.01 buffer solution into a clean polyethylene beaker and press the calibration button to start calibration; wait for the instrument test to stabilize (the display screen appears), and then add 7.00 and 9.21 buffer solutions in turn for calibration; after the three buffer solutions are calibrated, save or recalibrate according to the calibration results.

[0217] Test: Accurately weigh 5.00±0.01g of the powdered material on a scale and place it in a 100ml glass beaker. Add 30ml of pure water and stir thoroughly with a glass rod until the powder is completely dispersed in the pure water. Ultrasonicate in an ultrasonic cleaner for 5 minutes, then remove and allow to stand. Measure the pH of the supernatant using a pH tester and read the value.

[0218] After the above tests, the negative electrode materials prepared in Examples 1 to 8 and Comparative Example 1 have sample numbers S1 to S8 and R1 respectively. The performance parameters of the negative electrode materials are shown in Table 1:

[0219] Table 1

[0220] Table 2 Parameter performance comparison of each battery

[0221] As shown in Table 2, the negative electrode materials prepared in Examples 1 to 8, the negative electrode materials introduce Mg, Al, and P elements, and the Mg, Al, and P elements are coordinated with the O element in the silicon-based active material or the lithium silicate, which can be beneficial to the formation of lithium ion transmission channels, improve the rate performance of the negative electrode material, control the range of (a+b) / c, and the Mg, Al, P elements, the silicon-based active material and the lithium silicate can form faster and more lithium ion transmission channels, and reduce the lithium ion transmission energy barrier; and the introduction of Mg, Al, and P elements can reduce the hydrolysis of lithium silicate, thereby reducing the pH value of the negative electrode material and reducing the damage to the binder in the electrode sheet, which is beneficial to improving the processing stability problem of the pre-lithium negative electrode material. The slurry obtained by modulating the negative electrode material is more stable and not easy to settle or produce gas.

[0222] In Example 5, since the value of a+b+c is relatively small, the content of doping elements in the negative electrode material is too small, the magnesium aluminum phosphate substance formed on the surface of the silicon-based active material is insufficient, the pH value of the material increases, and the alkalinity is greater. After the negative electrode material is prepared to form a slurry, the stability of the slurry decreases, and a very small amount of gas production will occur after the storage time increases.

[0223] During the preparation of the negative electrode material of Comparative Example 1, the carbon-coated silicon oxide material is directly pre-lithiated. The lithium-doped silicon oxide material contains lithium silicate. Due to the hydrolysis of lithium silicate, the alkalinity is relatively high. When preparing the aqueous slurry, the alkaline aqueous solution destroys the polymer binder, causing the slurry to easily settle and produce gas, and the rate performance and cycle performance of the battery are also significantly reduced.

[0224] In the negative electrode material of Comparative Example 2, since (a+b) / c>1.5 and a+b+c≤0.5 in the negative electrode material, the ratio of Mg, Al, and P is unbalanced, the amount of P is too small, and the excess Mg and Al will excessively combine with Si and O to form magnesium silicate, aluminum silicate and other substances, causing silicon loss and a decrease in the specific capacity of the negative electrode material.

[0225] In the negative electrode material of Comparative Example 3, since (a+b) / c is less than 0.3 and a+b+c≤0.5 in the negative electrode material, the ratio of Mg, Al, and P is unbalanced, the amount of Mg and Al is too small, and the excess P combines with the pre-lithiation doped Li to form lithium phosphate, resulting in the loss of active lithium ions and the reduction of the initial efficiency of the negative electrode material.

[0226] Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the claims. Any person skilled in the art may make several possible changes and modifications without departing from the concept of the present application. Therefore, the scope of protection of the present application shall be based on the scope defined by the claims of the present application.

Claims

1. A negative electrode material, characterized in that: The negative electrode material includes silicon-based active material and lithium silicate; The negative electrode material further includes Mg, Al and P. The mass content of Mg in the negative electrode material is a%, the mass content of Al in the negative electrode material is b%, the mass content of P in the negative electrode material is c%, and in the negative electrode material, a, b and c satisfy the following relationship: 0.3≤(a+b) / c≤1.5, and 0.5≤a+b+c≤10.

2. The negative electrode material according to claim 1, characterized in that The negative electrode material includes at least one of the following features (1)-(2): (1) The silicon-based active material comprises silicon grains, and the size of the silicon grains is ≤20 nm; (2) The silicon-based active material includes silicon and / or silicon oxide.

3. The negative electrode material according to claim 1, characterized in that In the negative electrode material, 0.002≤a / b≤2.

4. The negative electrode material according to claim 1, characterized in that The negative electrode material includes at least one of the following features (1)-(3): (1)0.001≤a≤0.065； (2)0.09≤b≤0.55； (3)0.15≤c≤0.70。 5. The negative electrode material according to claim 1, characterized in that The negative electrode material also includes a carbon layer.

6. The negative electrode material according to claim 5, characterized in that The negative electrode material includes at least one of the following features (1)-(3): (1) The carbon layer includes at least one of an amorphous carbon material and a graphitized carbon material; (2) The carbon layer includes an amorphous carbon material, and the amorphous carbon material includes at least one of amorphous carbon, carbon black, and activated carbon; (3) The carbon layer includes a graphitized carbon material, and the graphitized carbon material includes at least one of conductive graphite and graphene.

7. The negative electrode material according to claim 1, characterized in that The particle size distribution of the negative electrode material satisfies: D 10 ≥1.0μm, 3μm≤D 50 ≤10μm, D 90 ≤25.0μm.

8. The negative electrode material according to claim 1, characterized in that The negative electrode material includes at least one of the following features (1)-(3): (1) The mass content of lithium silicate in the negative electrode material is 30% to 80%; (2) The lithium silicate includes at least one of Li2SiO3, Li2Si2O5, and Li4SiO4; (3) The pH value of the negative electrode material is 9 to 12.

9. The negative electrode material according to claim 1, characterized in that The specific capacity of the negative electrode material is tested in the voltage range of 0 to 1.5 V. When the cut-off voltage is 0.3 V, the specific capacity of the negative electrode material is A. When the cut-off voltage is 0.4 V, the specific capacity of the negative electrode material is B. When the cut-off voltage is 0.5 V, the specific capacity of the negative electrode material is C, and the following relationship is satisfied: 0.7≤(CB) / (BA)≤1.

3.

10. A method for preparing a negative electrode material, characterized in that: The steps include: The silicon-based raw material is immersed in a phosphoric acid solution for surface modification, and a precursor is obtained by solid-liquid separation; A mixture including a precursor, a lithium source, a magnesium source and an aluminum source is heat-treated to obtain a negative electrode material, wherein the negative electrode material includes a silicon-based active material and lithium silicate, and further includes Mg element, Al element and P element, the mass content of Mg element in the negative electrode material is a%, the mass content of Al element in the negative electrode material is b%, and the mass content of P element in the negative electrode material is c%. In the negative electrode material, a, b, and c satisfy the following relationship: 0.3≤(a+b) / c≤1.5, and 0.5≤a+b+c≤10.

11. The preparation method according to claim 10, characterized in that: It meets at least one of the following characteristics: (1) The concentration of the phosphoric acid solution is 0.05 mol / L to 5 mol / L; (2) The immersion treatment time is 2 hours to 10 hours; (3) The solid-liquid separation includes at least one of filtration and centrifugation.

12. The preparation method according to claim 10, characterized in that: It meets one of the following characteristics: (1) The lithium source includes at least one of Li2O, Li2CO3, LiOH, Li, LiH, LiAlH4 and LiBH4; (2) the magnesium source comprises at least one of Mg2O, Mg, Mg(OH)2 and MgCl2; (3) The aluminum source includes at least one of Al2O3, Al, Al(OH)3 and AlCl3; (4) The temperature of the heat treatment is 400°C to 900°C.

13. The preparation method according to claim 10, characterized in that: Before the silicon-based raw material is immersed in a phosphoric acid solution for surface modification, the method further comprises: performing a carbon coating treatment on the silicon-based raw material to obtain a silicon-carbon composite, and using the silicon-carbon composite as the silicon-based active material.

14. The preparation method according to claim 10, characterized in that: After heat-treating the mixture containing the precursor, the lithium source, the magnesium source and the aluminum source, the method further comprises: carbon coating the heat-treated product.

15. A battery, characterized in that: The negative electrode material comprises the negative electrode material according to any one of claims 1 to 9 or the negative electrode material prepared by the preparation method according to any one of claims 10 to 14.

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