LTO-LFT composite lithium ion battery negative electrode material and preparation method thereof

Abstract

The present invention discloses an LTO-LFT composite lithium-ion battery negative electrode material and a preparation method thereof, which belong to the technical field of preparation of lithium-ion battery electrode materials. The preparation method comprises the following steps: a. using a lithium compound, an organic reducing agent and an industrial titanyl sulfate solution as raw materials for calcination pre-treatment to obtain a paste; b. placing the paste in a reducing atmosphere for calcination and then cooling; c. grinding the product and then aerobic calcination; d. carbonizing the product obtained in step c to obtain the product. The present invention provides an LTO-LFT composite lithium-ion battery negative electrode material and a preparation method thereof with a short preparation process, simple process, low manufacturing cost, high resource utilization and low waste emission, which can effectively solve the problems that the preparation method of the existing lithium-ion battery negative electrode material LTO is relatively complicated, the cost is high, the LTO capacity is low, and the charge and discharge platform of LFT alone as a negative electrode material is poor.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of lithium ion battery electrode materials, and specifically relates to an LTO-LFT composite lithium ion battery negative electrode material and a preparation method thereof. Background Art

[0002] The negative electrode material of lithium-ion batteries is an important component of lithium-ion batteries and has a decisive influence on the performance of lithium-ion batteries. 12 (LTO) is an excellent new "zero strain" material. During normal charge and discharge, the volume change of the electrode material is very small, the lithium insertion potential is 1.55V, and each molecular unit can embed 3 lithium ions. During the charge and discharge process of the battery, the LTO crystal structure can maintain a high degree of stability, with excellent cycle performance and a stable discharge platform. LTO has three-dimensional channels, which can provide conditions for the rapid transmission of lithium ions. Its higher lithium insertion potential also solves the problem of lithium dendrites on the surface of the electrode material, avoiding the risk of short circuit caused by lithium dendrites piercing the diaphragm, resulting in the connection between the positive and negative electrodes. However, lithium titanate has a low electronic conductivity of about 10 because it is not conductive in itself. -7 -10 -9 S / cm. Spinel-type LiFeTiO4 (LFT) is an electrode material with cheap and abundant raw materials, environmental friendliness, and high specific capacity. LFT has the possibility of intercalating and deintercalating two lithium ions, at which point its theoretical capacity can reach 306mAh·g -1 , higher than LTO, but its charge and discharge platform is not obvious, which is much worse than LTO.

[0003] Prior art techniques have addressed the problem of poor overall electrochemical performance due to poor material conductivity. A common approach to addressing this issue is to dope the electrode material with various ions of both homovalent and heterovalent states, including metal and non-metallic ions. In most cases, these ions are incorporated individually. However, in recent years, research on co-doping with multiple impurities has increased, yielding positive performance improvements. Within the field of multiphase composite modification, a common approach for modifying poorly conductive electrode materials is carbon coating, a specialized two-phase composite. However, various methods exist, and most are complex to operate and require high raw materials, resulting in high costs. Other multiphase composite modifications are also an important approach for LTO modification. In addition to amorphous carbon, metals such as Ag are also currently used for coating. In terms of bulk composite modification, composite modification with graphite, Fe₃O₄, Fe₂O₃, and TiO₂ has also been proposed, achieving positive results. However, these composites exhibit significant structural differences from the bulk material, making it difficult to achieve optimal structural and performance coordination with the bulk material. LTO and LFT both have spinel structures and are characterized by minimal volume change during charge and discharge. LTO offers a good charge-discharge platform but a slightly lower capacity, while LFT has a higher capacity but a poorer charge-discharge platform. Combining the two with high compatibility, leveraging their strengths and compensating for their weaknesses, can comprehensively improve the performance of the composite electrode material. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that the preparation method of the existing lithium-ion battery negative electrode material LTO is relatively complex, the cost is high, the LTO capacity is low, and the charge and discharge platform of LFT alone as a negative electrode material is poor.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a method for preparing an LTO-LFT composite lithium-ion battery negative electrode material, comprising the following steps:

[0006] a. A lithium compound, an organic reducing agent and an industrial titanyl sulfate solution are used as raw materials for pre-calcination treatment to obtain a paste;

[0007] b. The paste obtained in step a is placed in a reducing atmosphere, calcined at 700-900 ℃ for 10-30min and then cooled;

[0008] c. The product obtained in step b was ground and then calcined in the presence of oxygen at 650-950 ° C for 1.5-8h, and then ground after cooling to obtain a LTO-LFT two-phase composite spinel electrode material;

[0009] d. The product obtained in step c is carbon-coated to obtain a carbon-coated LTO-LFT composite lithium-ion battery negative electrode material.

[0010] In the above step a, the calcination pretreatment is to dissolve the lithium compound and the organic reducing agent in an industrial titanyl sulfate solution, and heat and evaporate them to a paste under stirring. The molar ratio of C atoms in the organic reducing agent to S atoms in the industrial titanyl sulfate solution is 0.75-1.50:1.

[0011] In the above step a, the calcination pretreatment is to adjust the pH of the industrial titanyl sulfate solution to 9-10 with 5-10 mol / L ammonia water, obtain a multi-element mixed doped orthotitanate precursor raw material (undried aqueous state) after centrifugation, and then add a lithium compound and an organic reducing agent, grind and mix evenly to obtain a paste, wherein the total mass of the carbon element in the organic reducing agent accounts for 15%-50% of the mass of the orthotitanate precursor raw material.

[0012] In the above step a, the calcination pretreatment is to adjust the pH of the pre-diluted 10-fold industrial titanyl sulfate solution to 6-10 using 0.5-2 mol / L ammonia water, and obtain the orthotitanic acid precursor raw material (undried aqueous state) after vacuum filtration and washing, and then add the lithium compound and the organic reducing agent, grind and mix evenly to obtain a paste, wherein the total mass of the carbon element in the organic reducing agent accounts for 15%-50% of the mass of the orthotitanic acid precursor raw material.

[0013] The total titanium content in the industrial titanyl sulfate solution is approximately 160-200 g / L, with the remainder being Fe, S and a small amount of Al, Mg and Mn impurities, wherein the mass ratio of iron to titanium is 0.3-0.5:1.

[0014] The lithium compound is a lithium-containing compound that is easily decomposed at high temperature and is at least one of lithium hydroxide, lithium carbonate, lithium sulfate, lithium nitrate, and lithium acetate; the molar ratio of lithium atoms in the lithium compound to titanium atoms in the industrial titanyl sulfate solution is 0.9-1.1:1.

[0015] The organic reducing agent is a carbohydrate, which is at least one of glucose, sucrose, starch and citric acid.

[0016] In the above step d, the carbon coating is performed by mixing the product obtained in step c with a high-concentration glucose solution, grinding and pressing the mixture into sheets, and drying the mixture. The mixture is then buried with flake graphite powder and subjected to microwave carbon coating. The microwave power is controlled to be 700-800W, and the microwave treatment time is 3-4 minutes to obtain an LTO-LFT composite lithium-ion battery negative electrode material.

[0017] The above-mentioned grinding and tableting is performed by grinding the product of step c, adding it to a high-concentration glucose solution, grinding and mixing it, drying it appropriately at 60-70°C, grinding and granulating it, loosely pressing it into round tablets with a thickness of 0.5-0.8 cm, and completely drying it at 90°C; the mass of glucose in the high-concentration glucose solution accounts for 20-40% of the mass of the product of step c.

[0018] The above-mentioned complete coverage means that the thickness of the upper and lower flake graphite powders on the circular piece in the crucible is 0.45-0.55 cm respectively.

[0019] The LTO-LFT composite lithium-ion battery negative electrode material is prepared by the above-mentioned method for preparing the LTO-LFT composite lithium-ion battery negative electrode material.

[0020] The beneficial effects of the present invention are as follows: the industrial titanyl sulfate solution contains a large amount of iron ions, titanium ions and other components, as well as a small amount of impurity components such as aluminum, magnesium, and manganese, which are also the doping elements of lithium-ion battery electrode materials that have been widely studied. Therefore, by utilizing the various elemental resources in the industrial titanyl sulfate solution in an appropriate manner, in addition to providing the titanium and iron main component elements required for the negative electrode material of the LTO-LFT composite lithium-ion battery, it can also provide doping elements such as aluminum, magnesium, manganese, and sulfur, thereby achieving a multi-phase composite of the electrode material, comprehensively improving the electrode performance, and also achieving multi-element co-doping modification. In addition, the most traditional preparation method of lithium titanate and lithium iron titanate is to use analytically pure TiO2, Fe2O3 and LiOH / Li2CO3 as raw materials, mix them evenly, and calcine them at high temperature (600-1000°C) to obtain LTO or LFT powder. Considering the production process of the above-mentioned analytically pure raw materials, the production process of these methods is very lengthy and cumbersome, and needs to be appropriately improved.

[0021] The present invention uses titanium and iron in industrial titanyl sulfate solution as titanium sources and iron sources for synthesizing LTO-LFT composite negative electrode materials, combines the excellent charge and discharge platform performance of LTO with the higher electrochemical capacity of LFT, and utilizes a small amount of impurities such as aluminum, magnesium, and manganese in the industrial titanyl sulfate solution as co-doping components of the negative electrode material. A special microwave carbon coating treatment is adopted to finally obtain a carbon-coated LTO-LFT two-phase composite Al, Mg, Mn, S and other co-doped lithium ion battery negative electrode material, thereby comprehensively modifying the electrochemical properties of the negative electrode material.

[0022] Industrial titanyl sulfate solution contains a large amount of sulfur element, while in the new modified multiphase LTO-LFT negative electrode material proposed in this patent, sulfur is only used as a doping element, not a main component element, so in the technical solution of the present invention, sulfur element needs to be separated out in large quantities. The main components of titanium and iron in the negative electrode material, as well as a small amount of doping elements such as aluminum, magnesium, manganese, and sulfur are all directly derived from industrial titanyl sulfate solution. Since there is no longer a lengthy and tedious purification process for the relevant components, the process cost of manufacturing the negative electrode material proposed by the present invention is low, the process flow is simple, and resources can be fully utilized. In addition, the waste emissions of the preparation method of the present invention are less than those of direct sewage treatment. There are only ammonium sulfate solution and high-concentration sulfur dioxide flue gas generated by the desulfurization process. If the all-titanium liquid method is adopted, only high-concentration sulfur dioxide flue gas will be generated.

[0023] The present invention provides a novel modified LTO-LFT composite lithium-ion battery negative electrode material and a preparation method thereof, which have a short preparation process, simple process, low manufacturing cost, high resource utilization rate, and low waste emission. The preparation process is greatly shortened compared with the current commercial material preparation process, saves energy and reduces consumption, and reduces emissions in a green way, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a rate diagram of a battery equipped with the LTO-LFT composite lithium-ion battery negative electrode material of Example 6 of the present invention;

[0025] Figure 2 This is an impedance diagram of a battery equipped with the LTO-LFT composite lithium-ion battery negative electrode material according to Example 4 of the present invention;

[0026] Figure 3 The cyclic voltammogram of the battery equipped with the LTO-LFT composite lithium ion battery negative electrode material of Example 2 of the present invention;

[0027] Figure 4 This is the XRD pattern of the LTO-LFT composite lithium-ion battery negative electrode material according to Example 1 of the present invention;

[0028] Figure 5 This is an SEM image of the LTO-LFT composite lithium-ion battery negative electrode material of Example 5 of the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention can be implemented in the following manner.

[0030] The preparation method of the LTO-LFT composite lithium-ion battery negative electrode material comprises the following steps:

[0031] a. A lithium compound, an organic reducing agent and an industrial titanyl sulfate solution are used as raw materials for pre-calcination treatment to obtain a paste;

[0032] b. The paste obtained in step a is placed in a reducing atmosphere, calcined at 700-900 ℃ for 10-30min and then cooled;

[0033] c. The product obtained in step b was ground and then calcined in the presence of oxygen at 650-950 ° C for 1.5-8h, and then ground after cooling to obtain a LTO-LFT two-phase composite spinel electrode material;

[0034] d. The product obtained in step c is carbon-coated to obtain a carbon-coated LTO-LFT composite lithium-ion battery negative electrode material.

[0035] In step a, the pre-calcination treatment involves dissolving a lithium compound and an organic reducing agent in an industrial titanyl sulfate solution and heating and evaporating the solution with stirring until it forms a paste. The molar ratio of carbon atoms in the organic reducing agent to sulfur atoms in the industrial titanyl sulfate solution is 0.75-1.50:1. This method preserves all elemental resources in the industrial titanyl sulfate solution, with the vast majority of the sulfur being recovered as high-concentration sulfur dioxide flue gas. A very small amount of sulfur and other elements (such as aluminum, magnesium, and manganese) remain in the negative electrode material as co-doping elements, modifying its electrochemical properties.

[0036] In the above step a, the calcination pre-treatment is to adjust the pH of the industrial titanyl sulfate solution to 9-10 using 5-10 mol / L ammonia water, and obtain a multi-element mixed doped orthotitanate precursor raw material (undried aqueous state) after centrifugation, and then add a lithium compound and an organic reducing agent, grind and mix evenly to obtain a paste, and the total mass of carbon element in the organic reducing agent accounts for 15%-50% of the mass of the orthotitanate precursor raw material. While obtaining the multi-element mixed doped orthotitanate precursor raw material, a high-concentration ammonium sulfate centrifuge supernatant can also be obtained. Most of the added ammonia, nitrogen and part of the sulfur element are recovered in the form of ammonium sulfate. This method can control the content of sulfur element in the orthotitanate precursor raw material and reduce the amount of organic reducing agent used.

[0037] In the above step a, the calcination pre-treatment is to adjust the pH value of the industrial titanyl sulfate solution diluted 10 times in advance to 6-10 using 0.5-2mol / L concentration of ammonia water, and obtain an orthotitanic acid precursor raw material (undried aqueous state) after vacuum filtration and washing, and then add a lithium compound and an organic reducing agent, grind and mix evenly to obtain a paste, in which the total mass of carbon element in the organic reducing agent accounts for 15%-50% of the mass of the orthotitanic acid precursor raw material. A low-concentration ammonium sulfate aqueous solution is obtained while obtaining the orthotitanic acid precursor raw material. If there is no need to recover ammonium sulfate therefrom, it can be directly treated as ammonium nitrogen wastewater or used as liquid nitrogen fertilizer. In this way, the content of elements such as Fe, Mg, and S in the obtained orthotitanic acid precursor raw material can be adjusted. The flue gas generated during the subsequent calcination of the synthetic sample is still a high-concentration sulfur dioxide flue gas, which is beneficial to the recovery of sulfur element.

[0038] The total titanium content of the industrial titanyl sulfate solution is approximately 160-200 g / L, with the remainder being Fe, S, and small amounts of Al, Mg, and Mn impurities. The mass ratio of iron to titanium is 0.3-0.5:1. The present invention does not have strict requirements on the composition of the industrial titanyl sulfate solution; any intermediate material produced by a mature and stable industrial process can be used.

[0039] The lithium compound is a lithium-containing compound that is easily decomposed at high temperature and is at least one of lithium hydroxide, lithium carbonate, lithium sulfate, lithium nitrate, and lithium acetate; the molar ratio of lithium atoms in the lithium compound to titanium atoms in the industrial titanyl sulfate solution is 0.9-1.1:1.

[0040] The organic reducing agent is a carbohydrate, which is at least one of glucose, sucrose, starch and citric acid.

[0041] In the above step b, the placing in a reducing atmosphere is to cover the calcining crucible and use the CO generated by the pyrolysis of the organic reducing agent added to the material at high temperature to form a reducing atmosphere.

[0042] In the above step c, the grinding time is 15 minutes, and the aerobic calcination is performed by placing the material into an uncovered crucible for calcination. The calcined product mainly consists of spinel LTO and spinel LFT.

[0043] In step d, the carbon coating is performed by mixing the product obtained in step c with a high-concentration glucose solution, grinding, pressing, and drying the pellets. The pellets are then covered with flake graphite powder and microwave-coated. The microwave power is controlled at 700-800W, and the microwave treatment time is 3-4 minutes. This yields the LTO-LFT composite lithium-ion battery anode material. The carbon-coated pellets are a typical black color, with a uniform color across the surface and the interior.

[0044] The above-mentioned grinding and tableting is performed by grinding the product of step c, adding it to a high-concentration glucose solution, grinding and mixing it, drying it appropriately at 60-70°C, grinding and granulating it, loosely pressing it into round tablets with a thickness of 0.5-0.8 cm, and completely drying it at 90°C; the mass of glucose in the high-concentration glucose solution accounts for 20-40% of the mass of the product of step c.

[0045] The high-concentration glucose solution is prepared by mixing glucose and water in a mass ratio of 1:1, and heating the mixture at 60-70° C. to obtain the high-concentration glucose solution.

[0046] The above-mentioned complete coverage means that the thickness of the upper and lower flake graphite powders on the circular piece in the crucible is 0.45-0.55 cm respectively.

[0047] The LTO-LFT composite lithium-ion battery negative electrode material is prepared by the above-mentioned method for preparing the LTO-LFT composite lithium-ion battery negative electrode material.

[0048] The technical solutions and effects of the present invention are further illustrated below through practical examples.

[0049] Example

[0050] The present invention provides six groups of Examples 1-6 for preparing LTO-LFT composite lithium-ion battery negative electrode materials using the technical solution of the present invention, as follows.

[0051] Example 1

[0052] An appropriate amount of industrial titanyl sulfate solution was weighed (due to the high viscosity of the solution, the present invention uses weighing for measurement), glucose was added at a C:S mass ratio of 1.50, and lithium hydroxide was added at a Li:Ti molar ratio of 1.1. The mixture was stirred and evaporated at 90°C until it became a paste (no natural fluidity), then transferred to a covered ceramic crucible and placed in a 700°C muffle furnace for calcination for 30 minutes (after the sample was placed in the muffle furnace, the timer was started when the muffle furnace temperature returned to 700°C). The sample was removed, cooled, and ground, then placed in a crucible and placed in an 850°C muffle furnace for a second calcination. After 2 hours, the sample was removed, cooled, and ground. The product was mainly composed of spinel LTO and spinel LFT.

[0053] Glucose (15% by mass of the product) was weighed and dissolved in water at 60-70°C. While still hot, the product powder was added to the mixture, ground evenly, and dried at 60-70°C until easily granulated. The pellets were then loosely pressed into 0.5-0.8 cm thick discs. The discs were then covered with flake graphite powder in a quartz glass crucible and covered. The resulting mixture was microwaved in a 700-800W microwave oven for 3 minutes to yield the LTO-LFT composite lithium-ion battery anode material.

[0054] After the negative electrode material is assembled into a battery (metal lithium is the negative electrode), the first charge and discharge specific capacity is 209.24mAh / g. Figure 4 This is the XRD pattern of the LTO-LFT composite lithium-ion battery negative electrode material obtained in Example 1. It can be seen from the figure that the intensity ratio of the two strongest peaks (peaks at around 18° and around 35°) is inconsistent in any phase, while the peak at around 18° is the strongest peak of LTO, and the peak at around 35° is the strongest peak of LFT. The peak positions of the two phases are consistent, but the peak intensity ratio is different. Therefore, the material is composed of two phases, LTO and LFT.

[0055] Example 2

[0056] The industrial titanyl sulfate solution was neutralized with 5 mol / L ammonia water to a pH of 10 under stirring. After neutralization, the reaction system was vigorously stirred for 5 minutes, and the slurry was added to a 50 mL plastic centrifuge tube. After centrifugation at 5000 rpm for 15 minutes, the supernatant was completely poured out. Multi-element mixed orthotitanic acid (wet state) was doped. Glucose (15% of the total solid mass of orthotitanic acid) and lithium acetate (Li:Ti = 0.9 (molar ratio) were added and ground evenly. The paste was placed in a covered crucible and placed in a muffle furnace at 900°C. It was calcined for 10 minutes and then removed. After cooling, it was ground, placed in a crucible, placed in a muffle furnace at 950°C, and calcined for 1.5 hours. After cooling, it was ground. The product mainly consisted of spinel LTO and spinel LFT.

[0057] According to the carbon coating method in Example 1, 20% glucose was added and microwave carbon coating was carried out for 4 minutes to obtain the LTO-LFT composite lithium ion battery negative electrode material.

[0058] The product was assembled into a battery, and its initial charge and discharge specific capacity was 176.49 mAh / g. Figure 3 The cyclic voltammogram of the battery installed in Example 2 shows that: a sharp reduction peak appears at around 1.4V, corresponding to the process of Li+ release; an oxidation peak appears at around 1.9V, indicating that Li + Good embedding behavior; the sample has shoulder peaks around 1.6V and 1.7V, which is due to the pseudocapacitance phenomenon caused by the composite lithium iron titanate, and has a larger capacitance than pure lithium titanate.

[0059] Example 3

[0060] A pre-diluted 10-fold industrial titanyl sulfate solution was neutralized with 0.5 mol / L ammonia solution under stirring to pH 6. After neutralization, stirring was continued for 5 minutes before vacuum filtration. The volume of the resulting orthotitanic acid filter cake was estimated, and water was added at a volume ratio of 1:1 for three washes to obtain orthotitanic acid (wet state). Glucose (50% of the total solids content of orthotitanic acid) and lithium sulfate (Li:Ti (molar ratio) = 1.0) were added and ground to obtain a uniform mixture. The paste was placed in a covered crucible and placed in a muffle furnace at 700°C for calcination for 30 minutes before removal. After cooling, the mixture was finely ground, placed in a crucible, and placed in a muffle furnace at 650°C for calcination for 8.0 hours. After natural cooling, the desired product was obtained, primarily composed of spinel LTO and spinel LFT.

[0061] According to the carbon coating method in Example 1, 40% glucose was added and microwave carbon coating was carried out for 3.5 minutes to obtain the LTO-LFT composite lithium ion battery negative electrode material.

[0062] After the carbon-coated product was assembled into a battery, its initial charge and discharge specific capacity was 123.65 mAh / g.

[0063] Example 4

[0064] Weigh an appropriate amount of industrial titanyl sulfate solution, add glucose at a C:S mass ratio of 0.75, and lithium carbonate at a Li:Ti molar ratio of 1.05. After bubbling stops, stir and evaporate at 90°C until it becomes a paste (no natural fluidity). Transfer the solution to a covered ceramic crucible and place it in a 900°C muffle furnace for calcination for 10 minutes (after the sample is placed in the muffle furnace, the timer starts when the muffle temperature returns to 900°C). Remove the sample, cool it, grind it, place it in a crucible, and place it in a muffle furnace at 750°C for a second calcination. After 6 hours, remove it, cool it, and grind it. The product is mainly composed of spinel LTO and spinel LFT.

[0065] According to the carbon coating method in Example 1, 30% glucose was added and microwave carbon coating was carried out for 4 minutes to obtain the LTO-LFT composite lithium ion battery negative electrode material.

[0066] After the negative electrode material is assembled into a battery, the first charge and discharge specific capacity is 187.59 mAh / g. Figure 2 This is the impedance diagram of the battery installed in Example 4. It can be seen from the figure that: the semicircle diameter is small, the charge transfer resistance is small, and the electronic conductivity of the material is good; its straight part is inclined at nearly 45°, the material has better pseudocapacitive performance, and the diffusion rate of lithium ions inside the material is faster.

[0067] Example 5

[0068] A pre-diluted 10-fold industrial titanyl sulfate solution was neutralized with 2 mol / L ammonia solution under stirring to a pH of 10. After neutralization, stirring was continued for 5 minutes before vacuum filtration. The volume of the resulting orthotitanic acid filter cake was estimated, and water was added at a volume ratio of 1:1 for three washes to obtain orthotitanic acid (wet state). Glucose (35% of the total solids content of orthotitanic acid) and lithium nitrate (Li:Ti (molar ratio) = 0.95) were added and ground to form a uniform paste. The paste was placed in a covered crucible and placed in a muffle furnace at 800°C for calcination for 20 minutes before removal. After cooling, the mixture was finely ground, placed in a crucible, and placed in a muffle furnace at 700°C for calcination for 2.0 hours. After natural cooling, the desired product was obtained, primarily composed of spinel LTO and spinel LFT.

[0069] According to the carbon coating method in Example 1, 25% glucose was added and microwave carbon coating was carried out for 3 minutes to obtain the LTO-LFT composite lithium ion battery negative electrode material.

[0070] After the carbon-coated product is assembled into a battery, its initial charge and discharge specific capacity is 109 mAh / g. Figure 5 This is an SEM image of the LTO-LFT composite lithium-ion battery negative electrode material obtained in Example 5. It can be seen from the figure that the material is composed of submicron particles and micron-sized particles, and the appearance of the two different-sized particles is also significantly different; and the large particles generally do not exceed 5 microns, which is more conducive to the release and embedding of lithium ions.

[0071] Example 6

[0072] A pre-diluted 10-fold industrial titanyl sulfate solution was neutralized with 1 mol / L ammonia solution under stirring to a pH of 10. After neutralization, stirring was continued for 5 minutes before vacuum filtration. The volume of the resulting orthotitanic acid filter cake was estimated and washed in situ three times with water at a volume ratio of 1:1 to obtain orthotitanic acid (wet state) I. The industrial titanyl sulfate solution (containing the same amount of titanium as orthotitanic acid I) was weighed, and glucose and lithium hydroxide (including the titanium in orthotitanic acid I) were added at a C:S mass ratio of 1.0 and a Li:Ti molar ratio of 1.1. The mixture was stirred and evaporated at 90°C to form a paste II (no natural flowability). Orthotitanic acid I and paste II were ground and mixed to obtain paste III. This method can be used to fine-tune the dopant content of the synthesized material. This mixed paste III was placed in a covered crucible in a muffle furnace at 850°C and calcined for 25 minutes before removal. After cooling, the mixture was finely ground, placed in a crucible, and calcined in a muffle furnace at 950°C for 4.0 hours. After natural cooling, the target product is obtained, which is mainly composed of spinel LTO and spinel LFT.

[0073] According to the carbon coating method in Example 1, 20% glucose was added and microwave carbon coating was carried out for 3 minutes to obtain the LTO-LFT composite lithium ion battery negative electrode material.

[0074] After the carbon-coated product was assembled into a battery, its initial charge and discharge specific capacity was 153.46 mAh / g. Figure 1 This is the rate diagram of the battery installed in Example 6. It can be seen from the figure that: its cycle stability is better at higher rates, the capacity at 10C rate is still close to 70mAh / g, and the capacity retention rate at high rates is better.

Claims

1. A method for preparing a negative electrode material for a LTO-LFT composite lithium-ion battery, characterized in that The steps include: a. A lithium compound, an organic reducing agent and an industrial titanyl sulfate solution are used as raw materials for pre-calcination treatment to obtain a paste; The total titanium content of the industrial titanyl sulfate solution is 160-200 g / L, with the remainder being Fe, S, and a small amount of Al, Mg, and Mn impurities, wherein the mass ratio of iron to titanium is 0.3-0.5:1; the molar ratio of lithium atoms in the lithium compound to titanium atoms in the industrial titanyl sulfate solution is 0.9-1.1:1; b. The paste obtained in step a is placed in a reducing atmosphere, calcined at 700-900 ℃ for 10-30min and then cooled; c. The product obtained in step b was ground and then calcined in the presence of oxygen at 650-950 ° C for 1.5-8h, and then ground after cooling to obtain a LTO-LFT two-phase composite spinel electrode material; d. The product obtained in step c is carbon-coated to obtain a carbon-coated LTO-LFT composite lithium-ion battery negative electrode material.

2. The method for preparing the negative electrode material of the LTO-LFT composite lithium ion battery according to claim 1, wherein: In step a, the calcination pre-treatment is to dissolve the lithium compound and the organic reducing agent in an industrial titanyl sulfate solution, and heat and evaporate them under stirring until they become a paste.

3. The method for preparing the negative electrode material of the LTO-LFT composite lithium ion battery according to claim 1, characterized in that: In step a, the calcination pretreatment is to adjust the pH of the industrial titanyl sulfate solution to 9-10 with 5-10 mol / L ammonia water, obtain a multi-element mixed doped orthotitanate precursor raw material after centrifugation, then add a lithium compound and an organic reducing agent, grind and mix evenly to obtain a paste.

4. The method for preparing the negative electrode material for LTO-LFT composite lithium-ion batteries according to claim 1, wherein: In step a, the calcination pretreatment is to adjust the pH of the pre-diluted 10-fold industrial titanyl sulfate solution to 6-10 using 0.5-2 mol / L ammonia water, obtain the orthotitanate precursor raw material after vacuum filtration and washing, and then add the lithium compound and the organic reducing agent, grind and mix evenly to obtain a paste.

5. The method for preparing the LTO-LFT composite lithium-ion battery negative electrode material according to any one of claims 1 to 4, characterized in that: The lithium compound is a lithium-containing compound that is easily decomposed at high temperature, and is at least one of lithium hydroxide, lithium carbonate, lithium sulfate, lithium nitrate, and lithium acetate.

6. The method for preparing the LTO-LFT composite lithium-ion battery negative electrode material according to any one of claims 1 to 4, characterized in that: The organic reducing agent is a carbohydrate, which is at least one of glucose, sucrose, starch and citric acid.

7. The method for preparing the negative electrode material of the LTO-LFT composite lithium ion battery according to claim 2, characterized in that: The molar ratio of carbon atoms in the organic reducing agent to S atoms in the industrial titanyl sulfate solution is 0.75-1.50:

1.

8. The method for preparing the LTO-LFT composite lithium-ion battery negative electrode material according to any one of claims 3 to 4, characterized in that: The total mass of carbon element in the organic reducing agent accounts for 15%-50% of the mass of the orthotitanate precursor raw material.

9. The method for preparing the negative electrode material for LTO-LFT composite lithium-ion batteries according to claim 1, characterized in that: In step d, the carbon coating is performed by mixing the product obtained in step c with a high-concentration glucose solution, grinding and pressing the mixture into sheets, and drying the mixture. The mixture is then buried with flake graphite powder and subjected to microwave carbon coating. The microwave power is controlled to be 700-800 W, and the microwave treatment time is 3-4 minutes to obtain an LTO-LFT composite lithium-ion battery negative electrode material.

10. The method for preparing the negative electrode material for LTO-LFT composite lithium-ion batteries according to claim 9, characterized in that: The grinding and tableting process comprises grinding the product of step c, adding it to a high-concentration glucose solution, grinding and mixing, drying it appropriately at 60-70° C., grinding and granulating it, loosely pressing it into discs with a thickness of 0.5-0.8 cm, and completely drying it at 90° C.; the mass of glucose in the high-concentration glucose solution accounts for 20-40% of the mass of the product of step c.

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