Preparation method of spinel-type lithium chromium titanate negative electrode material

Abstract

The present invention discloses a method for preparing a spinel-type lithium chromium titanate negative electrode material, which belongs to the field of lithium-ion battery electrode materials. The present invention grinds a low-valent compound of solid chromium or metallic chromium powder with a solid titanium compound, a solid lithium-containing compound, and a solid carbohydrate evenly, adds a trace amount of liquid medium to continue grinding and mixing, and then performs a thermal decomposition treatment; the material is taken out and cooled, then ground for a second time, and then placed in a muffle furnace for a second calcination. After cooling, it is ground and carbonized to obtain a spinel-type lithium chromium titanate negative electrode material. The method of the present invention has low preparation cost, is easy to operate and control, has a low reaction temperature, a high yield of the target product, good uniformity, and stable electrochemical performance, and can effectively solve the problem that the existing LCT preparation method is relatively complex and costly.

Description

Technical Field

[0001] The invention belongs to the field of lithium-ion battery electrode materials, and particularly relates to a method for preparing a spinel-type lithium chromium titanate negative electrode material. Background Art

[0002] Spinel lithium chromium titanate LiCrTiO4 (LCT) is a kind of lithium chromium titanate with similar structure and properties to spinel lithium titanate Li4Ti5O 12 (LTO) is a lithium-ion battery negative electrode material that is very similar to LCT. Like LTO, LCT has very little volume change during the process of lithium ion insertion and deinsertion, and is a typical "zero strain" electrode material. Both have very obvious charge and discharge platforms. Although the electrochemical capacity of LCT is smaller than that of LTO, the charge and discharge potential of LCT is also slightly lower than that of LTO. When assembled into a battery with the same positive electrode material, it has a larger electrochemical capacity. However, there is a significant difference in that the electronic conductivity and lithium ion migration coefficient of LCT are significantly larger than those of LTO, making it more suitable for charging and discharging under larger current conditions. Therefore, in the field of lithium-ion batteries, LCT has received more and more attention and research as a negative electrode material for lithium-ion batteries.

[0003] LCT synthesis methods can be broadly classified into two categories: liquid-phase and solid-phase. The most widely studied liquid-phase method is the sol-gel method, which requires the use of soluble lithium, chromium, and titanium compounds, as well as some organic compounds such as citric acid. This is costly and generally requires subsequent high-temperature calcination. Other approaches combine the sol-gel method with electrospinning technology to synthesize fibrous or rod-shaped LCT materials, but this process is more complex and expensive.

[0004] The solid-phase synthesis of LCT has been widely studied and applied. Patent CN113979475 uses two stages of wet ball milling (i.e., coarse grinding and sand milling) to prepare each raw material, followed by spray drying, and then calcining at 750-900°C for 4-24 hours to synthesize LCT. Patent CN116153557 uses a strongly oxidizing chromium compound containing Cr(VI) as an oxidant and organic substances such as glucose and citric acid as reducing agents to form a combustion synthesis reaction system. The combustion reaction is initiated at a temperature range of 750-950°C, allowing the synthesis of spinel-type LCT in a very short time with good crystallinity. However, the combustion synthesis method generally requires a very high level of control for industrial production, resulting in a high manufacturing cost and being more suitable for small-batch intermittent manufacturing processes.

[0005] Currently reported LCT synthesis methods are either cumbersome and time-consuming, or require very long synthesis times, typically greater than or equal to 8 hours, resulting in high synthesis costs. From the perspective of an electrode material, high temperatures or prolonged calcination do improve the crystallinity of LCT, but the resulting material exhibits coarse grains, lengthening the lithium ion insertion and extraction pathways, and consequently, poorer electrochemical performance. Therefore, some researchers have resorted to post-synthesis fine milling to reduce particle size, which can alleviate these issues to a certain extent, but this significantly increases the synthesis process and manufacturing costs. While liquid-phase synthesis offers advantages over traditional high-temperature solid-phase methods in certain performance aspects (such as mixing uniformity), its longer synthesis process and higher costs are generally coupled with subsequent high-temperature calcination. In essence, the process is not much different from the high-temperature solid-phase method. Summary of the Invention

[0006] The technical problem to be solved by the present invention is that the existing LCT preparation method is relatively complex and costly.

[0007] The technical solution adopted by the present invention to solve the technical problem is: a method for preparing a spinel-type lithium chromium titanate negative electrode material, comprising the following steps:

[0008] a. Grind the solid low-valent chromium compound or metallic chromium powder with the solid titanium compound, solid lithium compound, and solid carbohydrate until there is no granularity when twisted between fingers, and mix all the materials evenly;

[0009] b. Add a small amount of liquid medium as needed and continue grinding until uniform. The amount of liquid material should be sufficient to make the final mixed material appear as a paste without any fluidity.

[0010] c. The paste-like material is transferred to a crucible and placed in a muffle furnace at 500-700 ° C with a cover and calcined for 5-15min. After calcination, it is removed and air-cooled to room temperature, and then ground until the finger twist has no granular feel.

[0011] d. The material after step c was placed in a muffle furnace at 650-740 ° C and calcined with the lid open for 1-4h. After calcination, it was immediately removed and air-cooled to room temperature. After grinding, a green spinel lithium chromium titanate powder material was obtained.

[0012] e. The green spinel lithium chromium titanate powder material is coated with carbon to obtain the lithium chromium titanate negative electrode material for lithium ion batteries.

[0013] In the above step a, the molar ratio of the low-valent chromium compound or metallic chromium powder, the titanium compound, the lithium compound and the carbohydrate is 7.2-8.8:7.2-8.8:6.4-9.6:1-3, wherein the carbohydrate is calculated as one unit of C6.

[0014] The above-mentioned low-valent chromium compound is at least one of chromium trioxide, chromium hydroxide, and chromium sulfate; the titanium compound is at least one of titanium dioxide, metatitanic acid, titanyl sulfate, and titanium sulfate; the lithium compound is at least one of lithium hydroxide, lithium carbonate, lithium sulfate, lithium acetate, and lithium chloride; and the carbohydrate is at least one of glucose, sucrose, and starch.

[0015] In the above step b, the trace liquid medium is polyethylene glycol 400, 95% ethanol or water.

[0016] In the above step c, the paste-like material occupies 1 / 2-2 / 3 of the volume of the crucible.

[0017] In the above step c, the calcined product is pure black after grinding.

[0018] In the above step d, the calcined product is uniformly green inside and out, with no black carbon residue.

[0019] In the above step e, the carbon coating process is as follows:

[0020] A. Dissolve PEG400 and glucose monohydrate in water at a mass ratio of 1:1 at 50-70°C to form a mixed saturated solution.

[0021] B. Maintaining a constant temperature, mix the green spinel lithium chromium titanate powder material with the saturated solution at a mass ratio of 1:0.5-0.7;

[0022] C. Transfer the above mixture into a crucible and place it into a muffle furnace and calcine at 700-800°C with a cover for 5-10 minutes;

[0023] D. After calcination, take out the product immediately after cooling, open the lid, take out the calcined product, and grind it into fine powder to obtain pure black lithium chromium titanate negative electrode material for lithium-ion batteries.

[0024] In the above step C, the mixture shall not occupy more than 1 / 2 of the crucible volume.

[0025] The beneficial effects of the present invention are as follows: the present invention provides a method for preparing a spinel-type LCT material with low preparation cost, easy operation and control, low reaction temperature, high yield of the target product, good uniformity, and stable electrochemical properties. Compared with the previous typical high-temperature solid-phase synthesis technology, the LCT synthesis technology provided by the present invention has lower requirements for mixing treatment, shorter synthesis time, and lower synthesis temperature. The present invention combines carbon dispersion technology with two-stage grinding and two-stage heat treatment to synthesize spinel-type LCT materials with better crystallinity but smaller and more uniform particles in a shorter time and at a lower temperature. The composite heating saturated solution carbon coating technology proposed by the present invention has a fast carbon coating rate and a thin carbon layer coated on the surface of the electrode active material particles, which suppresses the formation of large-scale continuous amorphous carbon phases in the process of completing synthesis and carbon coating in one step, improves the conductivity of the material, and shortens the migration path of lithium ions to a certain extent. The LCT material obtained by the present invention with a shorter synthesis time and lower synthesis temperature exhibits good initial charge and discharge capacity and rate performance when assembled into a button-type lithium-ion battery.

[0026] The process of the present invention is simple and easy to implement, does not require repeated calcination, and does not require long-term high-temperature treatment. It does not require high equipment conditions and has low manufacturing costs. It is suitable for industrial-scale production and manufacturing, and the synthetic product has good performance. The lithium chromium titanate prepared by the present invention is used as a negative electrode material for lithium-ion batteries after being coated with carbon. It has fine particles and a high initial charge and discharge specific capacity, and has broad application prospects in the field of lithium-ion batteries. The preparation method of the present invention can also be applied to the chemical synthesis research of other functional materials and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the XRD pattern of the LCT without carbon coating in Example 1 of the present invention;

[0028] Figure 2 This is a charge and discharge rate diagram of a battery assembled with carbon-coated LCT according to Example 1 of the present invention;

[0029] Figure 3 This is the XRD pattern of the LCT without carbon coating in Example 2 of the present invention;

[0030] Figure 4 This is the XRD pattern of the LCT without carbon coating in Example 3 of the present invention;

[0031] Figure 5 This is a charge and discharge rate diagram of a battery assembled with carbon-coated LCT according to Example 3 of the present invention;

[0032] Figure 6 This is a TEM image of the carbon-coated LCT of Example 3 of the present invention;

[0033] Figure 7This is the XRD pattern of the LCT without carbon coating in Example 4 of the present invention;

[0034] Figure 8 This is a cyclic voltammogram of a battery assembled with carbon-coated LCT according to Example 4 of the present invention;

[0035] Figure 9 This is the XRD pattern of the LCT without carbon coating in Example 5 of the present invention;

[0036] Figure 10 This is a SEM photograph of the LCT without carbon coating according to Example 5 of the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention can be implemented in the following manner.

[0038] The technical solution of the present invention grinds a solid low-valent chromium compound or metallic chromium powder with a solid titanium compound, a solid lithium-containing compound, and a solid carbohydrate into a fine powder and uniformly mixes them. A trace amount of liquid medium is optionally added to continue grinding and mixing. The mixture is then transferred to a suitably sized crucible and placed in a constant-temperature muffle furnace for a brief thermal decomposition treatment. This converts the added carbohydrate into a large amount of amorphous carbon, which becomes a continuous medium in the pyrolyzed mixture, while the other components become dispersed phases. This material is removed, cooled, and then ground a second time. As the amorphous carbon phase, which serves as the continuous medium, is ground and refined, the other components become more evenly mixed and dispersed as the amorphous carbon phase disperses. This fine powder is then placed in the muffle furnace for a second calcination. As the amorphous carbon phase in the powder particles oxidizes and volatilizes, the limited number of raw material components bound within the amorphous carbon phase within the particles fully come into contact with each other, ultimately reacting to synthesize a spinel-structured lithium chromium titanate material.

[0039] The preparation method of the spinel-type lithium chromium titanate negative electrode material specifically comprises the following steps:

[0040] (1) Grind a low-valent solid chromium compound or metallic chromium powder with a solid titanium compound, a solid lithium compound, and a solid carbohydrate into fine powder (no granularity when twisted with fingers), and mix all the materials evenly;

[0041] (2) Add a small amount of liquid material as needed and continue grinding until uniform. The amount of liquid material should be sufficient to make the final mixed material appear as a paste without any fluidity.

[0042] (3) Transfer the paste-like material into a crucible of appropriate size, with the material occupying 1 / 2-2 / 3 of the crucible volume;

[0043] (4) placing the material in the covered crucible into a muffle furnace at a certain temperature for a short thermal decomposition treatment;

[0044] (5) Take out the material and cool it to room temperature in air before grinding it for the second time. The fineness is determined by the same standard as (1);

[0045] (6) placing the second ground powder into a muffle furnace at a certain temperature for a second calcination;

[0046] (7) After the calcination time is completed, the mixture is immediately taken out and cooled to room temperature in the air, and then ground to obtain a green spinel-type lithium chromium titanate powder material.

[0047] (8) After carbon coating, lithium chromium titanate negative electrode material for lithium-ion batteries can be obtained.

[0048] The molar ratios of the low-valent chromium compound (or metallic chromium powder), titanium compound, lithium source compound and carbohydrate (calculated based on glucose C6 as one unit) in step (1) are (7.2-8.8):(7.2-8.8):(6.4-9.6):(1-3) respectively.

[0049] The low-valent chromium compounds in step (1) include chromium trioxide Cr2O3, chromium hydroxide Cr(OH)3, and chromium sulfate Cr2(SO4)3; the titanium compounds include titanium dioxide, metatitanic acid, titanyl sulfate, and titanium sulfate; the lithium compounds include lithium hydroxide, lithium carbonate, lithium sulfate, lithium acetate, and lithium chloride; and the carbohydrates include glucose, sucrose, and starch.

[0050] The trace liquid medium added to the grinding mixture in step (2) is polyethylene glycol 400 (PEG400), 95% or more ethanol and water. Since ethanol evaporates quickly, it should be added during grinding. However, precisely because ethanol evaporates quickly, it is easier to control.

[0051] The brief thermal decomposition treatment in step (2) is performed at a temperature of 500-700°C and a holding time of 5-15 minutes to completely decompose the carbohydrates into amorphous carbon without excessive oxidation of the amorphous carbon. A visual criterion for determining the calcination product is a pure black color after grinding. The calcination should be covered during the calcination.

[0052] In step (6), the calcination temperature is 650-740°C, and the calcination time is 1-4 hours. The furnace should be open during this stage to ensure full contact with the air in the furnace. The calcined product at this stage should be uniformly green inside and out, with no black carbon residue.

[0053] The carbonization process in step (8) is as follows:

[0054] A. Dissolve PEG400 and glucose monohydrate in water at a mass ratio of 1:1 at 50-70°C to form a mixed saturated solution.

[0055] B. Maintaining constant temperature, mix the powder with the saturated solution at a mass ratio of 1:(0.5-0.7);

[0056] C. Without drying, transfer the above mixture into a crucible (the mixture should not occupy more than 1 / 2 of the crucible volume) and cover it;

[0057] D. Place the covered crucible into a muffle furnace at 700-800°C and calcine for 5-10 minutes;

[0058] E. Immediately take out and cool, open the lid, take out the calcined product, and grind it into fine powder to obtain the carbon-coated lithium chromium titanate negative electrode material, which is pure black.

[0059] The technical solutions and effects of the present invention are further illustrated below through practical examples.

[0060] Example

[0061] Example 1.

[0062] According to the ratio of Cr:Ti:Li:C6=8:8:8.8:1, grind chromium trioxide for 2 minutes, then add titanium dioxide and continue grinding for 2 minutes, that is, grind for 2 minutes each time a raw material is added (lithium hydroxide monohydrate and glucose monohydrate will be added in this way later). Add appropriate amount of deionized water as needed to obtain a non-flowing paste-like substance, and continue grinding for 30 minutes. Transfer the paste-like material to a suitable crucible, with the material occupying 1 / 2 of the crucible volume. Transfer the covered crucible into a muffle furnace that has been kept at a constant temperature of 500°C, and immediately take it out and cool it in the air after pyrolysis at the constant temperature for 15 minutes. Grind the black cooled pyrolysis product until there is no granularity when twisted with fingers. Transfer the ground pyrolysis product to a muffle furnace that has been kept at a constant temperature of 650°C, and calcine it at the constant temperature for 4 hours without covering. After calcination, grind the product to obtain a spinel-type LCT product, and its XRD pattern is as shown below. Figure 1 As shown, the product has good crystallinity and basically no impurity phase exists.

[0063] At 50°C, glucose monohydrate and PEG400 were prepared into a saturated aqueous solution in a mass ratio of 1:1. The product and the saturated aqueous solution were evenly ground in a mass ratio of 1:0.6, transferred to a crucible, covered, and placed in a muffle furnace at a constant temperature of 750°C. After calcining for 5 minutes, the crucible was immediately taken out and cooled to room temperature in the air and then ground into powder to obtain a carbon-coated LCT negative electrode material.

[0064] The battery was assembled into a button-type lithium-ion battery to test its initial charge and discharge capacity. The charge cut-off voltage was 2.5 volts, the discharge cut-off voltage was 1.0 volts, and the current density was 0.15 mA / cm 2 Its first charge capacity reaches 135.5mAh / g at 0.2C. Figure 2The rate diagram of a button-type lithium-ion battery assembled with carbon-coated LCT material shows that, except for the 10C rate, the capacity changes at the other rates are not very large, and when it returns to 0.2C, its capacity is very close to the capacity at the initial 0.2C rate, indicating that the capacity is relatively stable at low rates.

[0065] Example 2

[0066] According to the ratio of Cr:Ti:Li:C6=8.8:8:8:2, grind chromium hydroxide Cr(OH)3 for 2 minutes, then add titanic acid and continue grinding for 2 minutes, that is, grind each raw material for 2 minutes (continue to add lithium carbonate and sucrose in this way later). Add appropriate amount of PEG400 as needed to obtain a non-flowing paste-like substance, and continue grinding for 30 minutes. Transfer the paste-like material to a suitable crucible, with the material occupying 3 / 4 of the crucible volume. Transfer the covered crucible into a muffle furnace that has been kept at a constant temperature of 700°C, and immediately take it out and cool it in the air after pyrolysis at constant temperature for 5 minutes. Grind the black cooled pyrolysis product until there is no granularity when twisted with fingers. Transfer the ground pyrolysis product to a muffle furnace that has been kept at a constant temperature of 740°C and calcine it at a constant temperature for 1 hour without covering. After calcination, grind the product to obtain a spinel-type LCT product, and its XRD pattern is as shown below. Figure 3 As shown, the product has good crystallinity and basically no impurity phase exists.

[0067] At 70°C, glucose monohydrate and PEG400 were prepared into a saturated aqueous solution in a mass ratio of 1:1. The product and the saturated aqueous solution were evenly ground in a mass ratio of 1:0.5, transferred to a crucible, covered, and placed in a muffle furnace at a constant temperature of 700°C. After calcination for 10 minutes, the crucible was immediately taken out and cooled to room temperature in the air and then ground into powder to obtain a carbon-coated LCT negative electrode material.

[0068] It was assembled into a button-type lithium-ion battery to test its initial charge and discharge capacity. At 0.2C, its initial charge capacity reached 125.3mAh / g.

[0069] Example 3.

[0070] According to the ratio of Cr:Ti:Li:C6=7.2:7.2:8:3, grind chromium sulfate Cr2(SO4)3 for 2 minutes, then add titanium sulfate and continue grinding for 2 minutes, that is, grind each raw material for 2 minutes (continue to add lithium sulfate and starch in this way later). Add appropriate amount of 95% ethanol as needed to obtain a non-flowing paste-like substance, and continue grinding for 30 minutes. Transfer the paste-like material to a suitable crucible, with the material occupying 3 / 5 of the crucible volume. Transfer the covered crucible into a muffle furnace that has been kept at a constant temperature of 600°C, and immediately take it out and cool it in the air after constant temperature pyrolysis for 10 minutes. Grind the black cooled pyrolysis product until there is no granularity when twisted with fingers. Transfer the ground pyrolysis product to a muffle furnace that has been kept at a constant temperature of 700°C, and calcine it at a constant temperature for 2.5 hours without covering. After calcination, grind the product to obtain a spinel-type LCT product, and its XRD pattern is as shown below. Figure 4 As shown, the product has good crystallinity and basically no impurity phase exists.

[0071] At 60°C, glucose monohydrate and PEG400 were prepared into a saturated aqueous solution in a mass ratio of 1:1. The product and the saturated aqueous solution were evenly ground in a mass ratio of 1:0.7, transferred to a crucible, covered, and placed in a muffle furnace at a constant temperature of 800°C. After calcination for 7.5 minutes, the crucible was immediately taken out and cooled to room temperature in the air and then ground into powder to obtain a carbon-coated LCT negative electrode material.

[0072] It was assembled into a button-type lithium-ion battery to test its initial charge and discharge capacity. At 0.2C, its initial charge capacity reached 140.7mAh / g. Figure 5 The rate diagram of a button-type lithium-ion battery assembled with carbon-coated LCT material shows that, except for the 10C rate, the capacity changes at the other rates are not very large, and when it returns to 0.2C, its capacity is very close to the capacity at the initial 0.2C rate, indicating that the capacity is relatively stable at low rates. Figure 6 This is a TEM image of the coated carbon sample of this embodiment. The carbon is wrapped on the surface of the LCT particles in the form of thin flakes and is relatively uniform. While improving the conductivity, it also has little hindrance to the insertion and extraction of lithium ions.

[0073] Example 4.

[0074] According to the ratio of Cr:Ti:Li:C6=8.8:8:9.6:2, grind chromium hydroxide Cr(OH)3 for 2 minutes, then add titanium oxysulfate and continue grinding for 2 minutes, that is, grind for 2 minutes each time a raw material is added (lithium acetate and glucose monohydrate will be added in this way later). Add appropriate amount of anhydrous ethanol as needed to obtain a non-flowing paste-like substance, and continue grinding for 30 minutes. Transfer the paste-like material to a suitable crucible, with the material occupying 1 / 2 of the crucible volume. Transfer the covered crucible into a muffle furnace that has been kept at a constant temperature of 650°C, and immediately take it out and cool it in the air after pyrolysis at a constant temperature for 7.5 minutes. Grind the black cooled pyrolysis product until there is no granularity when twisted with fingers. Transfer the ground pyrolysis product to a muffle furnace that has been kept at a constant temperature of 700°C and calcine it at a constant temperature for 2 hours without covering. After calcination, grind the product to obtain a spinel-type LCT product, and its XRD pattern is as shown below. Figure 7 As shown, the product has good crystallinity and basically no impurity phase exists.

[0075] At 65°C, glucose monohydrate and PEG400 were prepared into a saturated aqueous solution in a mass ratio of 1:1. The product and the saturated aqueous solution were evenly ground in a mass ratio of 1:0.5, transferred to a crucible, covered, and placed in a muffle furnace at a constant temperature of 700°C. After calcining for 6 minutes, the crucible was immediately taken out and cooled to room temperature in the air and then ground into powder to obtain a carbon-coated LCT negative electrode material.

[0076] It was assembled into a button-type lithium-ion battery to test its initial charge and discharge capacity. At 0.2C, its initial charge capacity reached 121.3mAh / g. Figure 8 The cyclic voltammetry curve of a button-type lithium-ion battery assembled with carbon-coated LCT material shows an oxidation peak potential of 1.59 V and a reduction peak potential of 1.43 V, which is basically consistent with the charge and discharge platform voltage of 1.55 V. This potential is consistent with the charge and discharge potential of lithium titanate negative electrode materials, indicating moderate potential and good safety.

[0077] Example 5.

[0078] According to the ratio of Cr:Ti:Li:C6=8.8:8.8:6.4:1, grind the metallic chromium powder (fineness>=120 mesh) for 2 minutes, then add titanic acid and continue grinding for 2 minutes, that is, grind each raw material for 2 minutes (continue to add lithium chloride and starch in this way). Add appropriate amount of anhydrous ethanol as needed to obtain a non-flowing paste-like substance, and continue grinding for 30 minutes. Transfer the paste-like material to a suitable crucible, with the material occupying 3 / 4 of the crucible volume. Transfer the covered crucible into a muffle furnace that has been kept at a constant temperature of 550°C, and immediately take it out and cool it in the air after constant temperature pyrolysis for 12.5 minutes. Grind the black cooled pyrolysis product until there is no granularity when twisted with fingers. Transfer the ground pyrolysis product to a muffle furnace that has been kept at a constant temperature of 670°C and calcine it at a constant temperature for 3 hours without covering. After calcination, grind the product to obtain a spinel-type LCT product, and its XRD pattern is as shown below. Figure 9 As shown, the product has good crystallinity and basically no impurity phase exists.

[0079] At 55°C, glucose monohydrate and PEG400 were prepared into a saturated aqueous solution in a mass ratio of 1:1. The product and the saturated aqueous solution were evenly ground in a mass ratio of 1:0.6, transferred to a crucible, covered, and placed in a muffle furnace at a constant temperature of 770°C. After calcination for 9 minutes, the crucible was immediately taken out and cooled to room temperature in the air and then ground into powder to obtain a carbon-coated LCT negative electrode material.

[0080] It was assembled into a button-type lithium-ion battery to test its initial charge and discharge capacity. At 0.2C, its initial charge capacity reached 131.6mAh / g. Figure 10 This is an SEM photo of LCT material without carbon coating. Its particles are relatively small and more uniform in size, basically around 100nm, with obvious agglomeration. Many pores are formed between the agglomerated particles, which is conducive to the full contact between the electrolyte solution and the electrode material, and also shortens the deintercalation and insertion distance of lithium ions.

Claims

1. A method for preparing a spinel-type lithium chromium titanate negative electrode material, characterized in that The steps include: a. Grind the solid low-valent chromium compound or metallic chromium powder with the solid titanium compound, solid lithium compound, and solid carbohydrate until there is no granularity when twisted between fingers, and mix all the materials evenly; b. Add a small amount of liquid medium as needed and continue grinding until uniform. The amount of liquid material should be sufficient to make the final mixed material appear as a paste without any fluidity. c. The paste-like material is transferred to a crucible and placed in a muffle furnace at 500-700 ° C with a cover and calcined for 5-15min. After calcination, it is removed and air-cooled to room temperature, and then ground until the finger twist has no granular feel. d. The material after step c was placed in a muffle furnace at 650-740 ° C and calcined with the lid open for 1-4h. After calcination, it was immediately removed and air-cooled to room temperature. After grinding, a green spinel lithium chromium titanate powder material was obtained. e. The green spinel lithium chromium titanate powder material is coated with carbon to obtain the lithium chromium titanate negative electrode material for lithium ion batteries.

2. The method for preparing the spinel-type lithium chromium titanate negative electrode material according to claim 1, characterized in that: In step a, the molar ratio of the low-valent chromium compound or metallic chromium powder, the titanium compound, the lithium compound and the carbohydrate is 7.2-8.8:7.2-8.8:6.4-9.6:1-3, wherein the carbohydrate is calculated as one unit of C6.

3. The method for preparing the spinel lithium chromium titanate negative electrode material according to claim 1 or 2, characterized in that: The low-valent chromium compound is at least one of chromium trioxide, chromium hydroxide, and chromium sulfate; the titanium compound is at least one of titanium dioxide, metatitanic acid, titanyl sulfate, and titanium sulfate; the lithium compound is at least one of lithium hydroxide, lithium carbonate, lithium sulfate, lithium acetate, and lithium chloride; and the carbohydrate is at least one of glucose, sucrose, and starch.

4. The method for preparing the spinel-type lithium chromium titanate negative electrode material according to claim 1, characterized in that: In step b, the trace liquid medium is polyethylene glycol 400, 95% ethanol or water.

5. The method for preparing the spinel lithium chromium titanate negative electrode material according to claim 1, characterized in that: In step c, the paste-like material occupies 1 / 2-2 / 3 of the volume of the crucible.

6. The method for preparing the spinel lithium chromium titanate negative electrode material according to claim 1, characterized in that: In step c, the calcined product is pure black after grinding.

7. The method for preparing the spinel lithium chromium titanate negative electrode material according to claim 1, characterized in that: In step d, the calcined product is uniformly green inside and out, with no black carbon residue.

8. The method for preparing the spinel lithium chromium titanate negative electrode material according to claim 1, characterized in that: In step e, the carbon coating process is as follows: A. Dissolve PEG400 and glucose monohydrate in water at a mass ratio of 1:1 at 50-70°C to form a mixed saturated solution. B. Maintaining a constant temperature, mix the green spinel lithium chromium titanate powder material with the saturated solution at a mass ratio of 1:0.5-0.7; C. Transfer the above mixture into a crucible and place it into a muffle furnace and calcine at 700-800°C with a cover for 5-10 minutes; D. After calcination, take out the product immediately after cooling, open the lid, take out the calcined product, and grind it into fine powder to obtain pure black lithium chromium titanate negative electrode material for lithium-ion batteries.

9. The method for preparing the spinel-type lithium chromium titanate negative electrode material according to claim 8, characterized in that: In step C, the mixture should not occupy more than 1 / 2 of the crucible volume.

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