Modified lithium titanate, preparation method thereof, negative electrode material, pole piece, lithium battery and electric device

Abstract

The invention relates to the field of lithium ion batteries, and discloses modified lithium titanate, a preparation method thereof, a negative electrode material, a pole piece, a lithium battery and an electric device. According to the invention, the binder is introduced for auxiliary coating in the tin dioxide coating process of the lithium titanate, so that on one hand, the structure of the tin dioxide coated lithium titanate is more stable, the conductivity, the rate capability and the cycle performance of the negative electrode material are improved, on the other hand, the gram volume of the modified lithium titanate can be further improved, and the service life of the negative electrode material is prolonged. The defect that the theoretical specific capacity of lithium titanate is low is overcome, and lithium titanate can be widely applied to portable electronic equipment and long-endurance electric automobiles.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and more particularly to a modified lithium titanate and its preparation method, as well as negative electrode materials, electrode sheets, lithium batteries, and electrical devices. Background Technology

[0002] Lithium titanate (Li4Ti5O) 12 Lithium-ion battery anode material (LTO) has attracted widespread attention due to its unique performance characteristics. LTO exhibits extremely high safety and stability, particularly its "zero-strain" characteristic, which results in minimal volume change (<1%) in its crystal structure (spinel structure) during lithium-ion insertion / extraction. This avoids material pulverization and electrode damage caused by repeated charge-discharge cycles, ensuring the structural integrity of the electrode. Thanks to its "zero-strain" characteristic and stable SEI film (or the absence of SEI film formation), LTO electrodes experience minimal mechanical stress during cycling, maintaining a well-preserved material structure and minimizing interfacial side reactions. Therefore, LTO batteries typically exhibit superior long-cycle performance. Furthermore, LTO batteries also demonstrate excellent rate performance.

[0003] However, the low energy density of LTO is its most significant drawback. The theoretical specific capacity of LTO is 175 mAh / g, which is far lower than the theoretical specific capacity of graphite (372 mAh / g). This is the biggest obstacle limiting its widespread application in portable electronic devices and long-range electric vehicles. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide a modified lithium titanate and a method for preparing the same, so that the specific capacity of the modified lithium titanate obtained by the preparation method is significantly improved;

[0005] Another objective of this application is to provide anode materials, anode sheets, lithium-ion batteries, and electrical devices based on the above-described modified lithium titanate.

[0006] To solve the aforementioned technical problems / achieve the aforementioned objectives, or at least partially solve the aforementioned technical problems / achieve the aforementioned objectives, as a first aspect of this application, a method for preparing modified lithium titanate is provided, comprising:

[0007] S1. Prepare lithium titanate solution and tin source material solution respectively using organic solvents;

[0008] S2. Add a tin source material solution dropwise to the lithium titanate solution to obtain a first mixed solution;

[0009] S3. Add the binder solution dropwise to the mixed solution to obtain a second mixed solution;

[0010] S4. Heat the second mixed solution until the solvent evaporates to obtain a gel-like solid;

[0011] S5. The gel-like solid is dried, pulverized, and sintered once to obtain a sintered material;

[0012] S6. The material to be sintered in the first stage is crushed and then sintered in the second stage to obtain the modified lithium titanate.

[0013] Optionally, the organic solvent includes N-methylpyrrolidone.

[0014] Optionally, the mass ratio of lithium titanate, tin source material, and binder is 10:0.3:(1.2-2.7). Further optionally, the lithium titanate comprises secondary lithium titanate particles, the tin source material comprises tin powder, and the binder comprises polyvinylidene fluoride.

[0015] Optionally, the temperature of the first sintering is 150-250℃, and the temperature of the second sintering is 300-500℃.

[0016] As a second aspect of this application, modified lithium titanate prepared by the preparation method described in this application is provided.

[0017] As a third aspect of this application, a negative electrode material is provided, comprising the modified lithium titanate described in this application, as well as a binder and a conductive agent.

[0018] As a fourth aspect of this application, a negative electrode sheet is provided, including a current collector and the negative electrode material described in this application coated on the surface of the current collector.

[0019] As a fifth aspect of this application, a lithium-ion battery is provided, including a positive electrode, a negative electrode as described in this application, a separator, and an electrolyte.

[0020] As a sixth aspect of this application, an electrical device is provided, including the lithium-ion battery described in this application, wherein the lithium-ion battery provides electrical energy to the electrical device.

[0021] This application introduces a binder for auxiliary coating during the tin dioxide coating process of lithium titanate. On the one hand, this makes the structure of tin dioxide coated lithium titanate more stable, thereby improving the conductivity, rate performance and cycle performance of the negative electrode material. On the other hand, it can further improve the specific capacity of modified lithium titanate, making up for the defect of low theoretical specific capacity of lithium titanate, so that lithium titanate can be widely used in portable electronic devices and long-range electric vehicles. Detailed Implementation

[0022] This application discloses a modified lithium titanate, its preparation method, as well as a negative electrode material, electrode sheet, lithium battery, and power device. Those skilled in the art can refer to the content of this application and appropriately modify the process parameters to achieve the desired results. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this application. The products, processes, and applications described in this application have been described through preferred embodiments. Those skilled in the art can obviously modify or appropriately change and combine the preparation methods described herein without departing from the content, spirit, and scope of this application to realize and apply the technology of this application. Obviously, the described embodiments are only some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application.

[0023] It should be noted that, in this document, relational terms such as "first" and "second," "step 1" and "step 2," and "(1)" and "(2)" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Moreover, the embodiments and features described in this application can be combined with each other without conflict.

[0024] The theoretical specific capacity of lithium titanate (LTO) is 175 mAh / g, far less than that of graphite (372 mAh / g). Especially in practical applications, the actual specific capacity of lithium titanate is further reduced by factors such as preparation process, material purity, doping modification, and testing conditions, typically ranging from 150 to 165 mAh / g. This significantly limits the application of this excellent "zero-strain" anode material.

[0025] Based on the low energy density of existing lithium titanate materials, the first aspect of this application provides a method for preparing modified lithium titanate, comprising:

[0026] S1. Prepare lithium titanate solution and tin source material solution respectively using organic solvents;

[0027] S2. Add a tin source material solution dropwise to the lithium titanate solution to obtain a first mixed solution;

[0028] S3. Add the binder solution dropwise to the mixed solution to obtain a second mixed solution;

[0029] S4. Heat the second mixed solution until the solvent evaporates to obtain a gel-like solid;

[0030] S5. The gel-like solid is dried, pulverized, and sintered once to obtain a sintered material;

[0031] S6. The material to be sintered in the first stage is crushed and then sintered in the second stage to obtain the modified lithium titanate.

[0032] In the modification method of this application, LTO is coated with tin source material, and SnO2 coating is formed through subsequent sintering process. SnO2 has semiconductor properties and its conductivity is significantly higher than that of LTO. Its coating layer can form a highly efficient electron transport network on the surface of LTO particles, reduce interface impedance, and improve charge and discharge efficiency. At the same time, it can also improve capacity retention at high rates and improve the cycle performance of the battery. In addition, SnO2 itself has a high theoretical specific capacity (782 mAh / g), and its coating layer can contribute additional lithium storage sites.

[0033] The binder plays two main roles in the modification method of this application: ① It increases the suspension of LTO, making it less prone to sedimentation and facilitating more uniform mixing of LTO and tin source materials; ② It has an adhesive effect, making it easier for the tin source material to adhere to the surface of lithium titanate. The adhesiveness of the binder makes it easier for the tin source material to coat the LTO surface, resulting in a more stable tin powder-coated lithium titanate structure, which is further enhanced by subsequent sintering to form a more stable SnO2-coated LTO. These two roles allow the binder to further improve the specific capacity of the modified lithium titanate.

[0034] Too little binder cannot fully achieve the above two effects, while too much binder will increase the content and reduce the proportion of SnO2-coated LTO, making the modified LTO material difficult to use and reducing the specific capacity. Therefore, in some embodiments of this application, the mass ratio of lithium titanate, tin source material (calculated as tin element) and binder is 10:0.3:(1.2-2.7), wherein the ratio parameter of binder can be selected from 1.2, 1.3, 1.4, 1.5, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2.0, 2.1, 2.4, 2.7 or any value between any two, and the mass ratio of lithium titanate, tin source material (calculated as tin element) and binder can be selected from 10:0.3:1.2, 10:0.3:1.5, 10:0.3:1.65, 10:0.3:1.8, 10:0.3:1.95, 10:0.3:2.1 or any ratio between any two.

[0035] In some embodiments of this application, the lithium titanate comprises LTO secondary particles, which are typically formed by the weak bonding aggregation of multiple LTO primary particles, with a size ranging from five to eighteen micrometers. The LTO secondary particles used in this application are formed by high-temperature sintering of primary particles. Compared to LTO nanoparticles of tens to hundreds of nanometers, they have a smaller specific surface area, reducing the contact area with the electrolyte, inhibiting the continuous growth of the CEI film, and improving coulombic efficiency and cycle stability. At the same time, the LTO secondary particles still retain the nanoscale size of the primary particles, shortening the lithium-ion diffusion path, ensuring rapid reaction kinetics, and providing electrolyte permeation channels through the pores inside the LTO secondary particles, accelerating ion transport. In addition, the LTO secondary particles can maintain their overall integrity during charging and discharging, avoiding pulverization. The LTO secondary particle structure achieves a balance between the advantages of the nanoscale and the practicality of the microscale through the "aggregation of small particles into large particles".

[0036] In some embodiments of this application, the tin source material includes tin powder, preferably nano-tin powder (10-20 nm). Nano-sized tin powder can form an ultra-thin, continuous SnO2 coating layer, improving the conductivity of LTO. Its spherical morphology and high specific surface area enhance the interfacial bonding with LTO, reducing the risk of coating layer detachment. Furthermore, nano-tin powder can be directly oxidized to SnO2 by calcination in an oxygen-containing atmosphere. The thickness can be precisely controlled by particle size and oxidation conditions, avoiding corrosion and material contamination of equipment by chlorine / acidic tin sources.

[0037] In some embodiments of this application, the binder includes polyvinylidene fluoride (PVDF). PVDF increases the suspendability of lithium titanate, making it less prone to sedimentation and allowing for more uniform mixing with tin powder. Furthermore, the adhesive properties of PVDF facilitate the adhesion of tin powder to the surface of lithium titanate, resulting in a more stable tin-coated lithium titanate structure and a more stable tin dioxide coating layer. Compared to other binders, PVDF is better suited to lithium titanate in these two aspects, significantly increasing its specific capacity.

[0038] In some embodiments of this application, the organic solvent includes N-methylpyrrolidone (NMP). In the modification process of this application, the binder solution can also be prepared using NMP. The advantage of using NMP is that it is typically used for dissolution when preparing the negative electrode slurry for subsequent modification of lithium titanate, thus avoiding the impact of incomplete solvent evaporation on the negative electrode slurry during the modification process.

[0039] In some embodiments of this application, the first sintering is a pre-sintering at a temperature of 150-250°C. The LTO / SnO2 precursor is initially formed through pre-sintering. At this time, the temperature should not be too high to avoid damaging the binder and hindering the adhesion and coating of the tin source material onto the LTO surface. The temperature of the first sintering can be selected from 150°C, 175°C, 200°C, 225°C, 250°C or any value between the two. The time of the first sintering can be selected from 1-5 hours. In some other embodiments of this application, the secondary sintering temperature is 300-500℃. After forming the LTO / SnO2 precursor, the precursor is completely oxidized to a SnO2 coating layer at a higher temperature to form the LTO / SnO2 material. At the same time, high-temperature sintering also helps to remove residual binder and avoid the influence of binder on the specific capacity of modified LTO. The secondary sintering temperature can be selected as 300℃, 350℃, 400℃, 450℃, 500℃ or any value between the two, and the secondary sintering time can be selected as 5-10h.

[0040] In a second aspect of this application, modified LTO prepared by the preparation method described herein is provided. Compared to modified LTO prepared without binder modification, the specific capacity of the modified LTO obtained by the process described in this application is significantly improved, by up to 11.4%.

[0041] In a third aspect of this application, a negative electrode material is provided, comprising the modified LTO described in this application, as well as a binder and a conductive agent, wherein their weight percentages are 90-98%:1-5%:1-5% respectively.

[0042] In some embodiments of this application, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0043] In some embodiments of this application, the adhesive includes an oil-based adhesive, such as at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin.

[0044] In a fourth aspect of this application, a negative electrode sheet is provided, comprising a current collector and the negative electrode material described in this application coated on the surface of the current collector. The negative electrode material is prepared by NMP slurry preparation, coated onto the current collector, and rolled and formed into a sheet to obtain the negative electrode sheet.

[0045] In some embodiments of this application, the current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0046] In a fifth aspect of this application, a lithium-ion battery is provided, including a positive electrode, a negative electrode as described in this application, a separator, and an electrolyte.

[0047] During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrode plates. The electrolyte acts as a conductor of ions between the positive and negative electrode plates. The separator, positioned between the positive and negative electrode plates, primarily prevents short circuits between the two electrodes while allowing ions to pass through.

[0048] This application does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be liquid, gel, or all-solid. In some embodiments of this application, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent. In other embodiments of this application, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, or lithium tetrafluorooxalate phosphate. In other embodiments of this application, the solvent may include at least one selected from ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethylene glycol dimethyl ether, methyl ethyl sulfone, or diethyl sulfone.

[0049] In some embodiments of this application, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0050] In some embodiments of this application, the positive electrode, the negative electrode, and the separator can be fabricated into an electrode assembly by a winding process or a stacking process.

[0051] In some embodiments of this application, the lithium-ion battery may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned electrode components and electrolyte. In other embodiments of this application, the outer packaging of the lithium-ion battery may be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the lithium-ion battery may also be a soft pack, such as a pouch.

[0052] In a sixth aspect of this application, an electrical device is provided, including the lithium-ion battery described in this application. The lithium-ion battery provides electrical energy to the electrical device and can also be used as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0053] In the comparative experiments provided in this application, unless otherwise specified, all experimental conditions and materials are kept consistent to ensure comparability. Unless otherwise specified, all experimental materials and reagents used in the examples are commercially available.

[0054] The following provides a further description of a modified lithium titanate, its preparation method, as well as the negative electrode material, electrode sheet, lithium battery, and power device provided in this application.

[0055] Example 1:

[0056] Weigh 10±0.0005g of lithium titanate, 0.3±0.0005g of nano tin powder (diameter 10-20nm), 6±0.0005g of PVDF, and 394g of NMP.

[0057] Take a 400mL beaker, add 100g NMP, then add 10g lithium titanate and sonicate at 100Hz for 10min in an ultrasonic cleaner while stirring with a glass rod to obtain A;

[0058] Take a 200mL beaker, add 100g NMP, then add 0.3g nano tin powder and sonicate at 100Hz for 20min in an ultrasonic cleaner while stirring with a glass rod to obtain B;

[0059] After ultrasonication, the lithium titanate solution was added to the rotor. The beaker was placed in a constant temperature magnetic stirring pot and rotated at 400 r / min for 10 min. After 10 min, the speed was reduced to 300 r / min, and the nano tin powder solution was added drop by drop to the solution.

[0060] After the liquid addition is complete, continue stirring at 400 r / min for 30 min to obtain mixture A+B;

[0061] Add 194g NMP to a stirred tank, slowly add 6g PVDF, rotate at 100r / min for 10min, then reduce the speed to 400r / min and stir until the PVDF particles dissolve to obtain C.

[0062] Add 40g of C dropwise to the A+B mixture at 300r / min. After the addition is complete, continue stirring at 400r / min for 30min to obtain D.

[0063] Raise the temperature to 90°C and heat and stir until the solution has mostly evaporated and formed a gel-like solid.

[0064] Transfer the gel-like solid onto a petri dish, bake at 100°C for more than 10 hours to dry it, and then let it cool to room temperature.

[0065] The dried solid powder was transferred to agate and ground for 1 hour.

[0066] The ground solid powder was transferred to a muffle furnace and pre-sintered at 200°C for 3 hours, then cooled to room temperature.

[0067] The pre-sintered solid powder (Li4Ti5O) 12 The SnO2 precursor was transferred to a mortar and ground for 30 minutes.

[0068] Then grind the Li4Ti5O again 12 The SnO2 precursor was transferred to a muffle furnace and sintered at 300°C for 6 hours. After cooling to room temperature, SnO2-coated lithium titanate S1 was obtained.

[0069] CR2032 button batteries were fabricated by coating lithium titanate, PVDF, and SP with SnO2 in a ratio of 90:5:5.

[0070] Example 2:

[0071] The process was prepared according to Example 1, except that the amount of solution C was 50g, resulting in SnO2-coated lithium titanate S2.

[0072] Example 3:

[0073] The SnO2-coated lithium titanate S3 was prepared according to the process in Example 1, except that the amount of solution C used was 60g.

[0074] Example 4:

[0075] The SnO2-coated lithium titanate S4 was prepared according to the process in Example 1, except that the amount of solution C used was 70g.

[0076] Example 5:

[0077] Prepared according to the process in Example 1, except that the amount of solution C used is 90g, to obtain SnO2-coated lithium titanate S5.

[0078] Comparative Example 1:

[0079] Prepared according to the process in Example 1, except that the amount of solution C is 0, to obtain SnO2-coated lithium titanate SO.

[0080] Comparative Example 2:

[0081] Prepared according to the process in Example 3, except that the binder is epoxy resin, resulting in SnO2-coated lithium titanate S3'.

[0082] Experimental example:

[0083] The specific capacity of the modified lithium titanate in each embodiment and comparative example was tested, and the results are shown in Table 1 below.

[0084] Table 1

[0085] Group 3% PVDF content (g) Capacity (mAh / g) promote% Comparative Example 1-S0 0 161.8 0 Comparative Example 2-S3' 60 165.6 2.3 Example 1-S1 40 169.6 4.6 Example 2-S2 50 177.4 8.8 Example 3-S3 60 182.7 11.4 Example 4-S4 70 178.4 9.3 Example 5-S5 90 168.9 4.4

[0086] According to the specific capacity test results in Table 1, the specific capacity of lithium titanate S0 obtained by the modification process without the addition of PVDF is only 161.8 mAh / g, which is significantly lower than the specific capacity of lithium titanate in each example group. After adding PVDF according to the modification process of this application, the specific capacity of the modified lithium titanate shows a trend of first increasing and then decreasing with the increase of PVDF content. The highest specific capacity of modified lithium titanate was obtained when 3% PVDF was added at 60g, with an improvement rate of 11.4%.

[0087] Comparative Example 2 replaced the binder with epoxy resin. The specific capacity of the modified lithium titanate S3' obtained was improved to some extent compared with lithium titanate S0, but the improvement rate was only 2.3%. Compared with the lithium titanate S3 obtained using the same amount of binder, the improvement rate was nearly 10%, and the specific capacity improvement effect was significantly worse than that of PVDF.

[0088] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A method for preparing modified lithium titanate, characterized in that, include: S1. Prepare lithium titanate solution and tin source material solution respectively using organic solvents; S2. Add a tin source material solution dropwise to the lithium titanate solution to obtain a first mixed solution; S3. Add the binder solution dropwise to the mixed solution to obtain a second mixed solution; S4. Heat the second mixed solution until the solvent evaporates to obtain a gel-like solid; S5. The gel-like solid is dried, pulverized, and sintered once to obtain a sintered material; S6. The material to be sintered in the first stage is crushed and then sintered in the second stage to obtain the modified lithium titanate.

2. The preparation method according to claim 1, characterized in that, The organic solvent includes N-methylpyrrolidone.

3. The preparation method according to claim 1, characterized in that, The mass ratio of lithium titanate, tin source material and binder is 10:0.3:(1.2-2.7).

4. The preparation method according to claim 1 or 3, characterized in that, The lithium titanate includes secondary lithium titanate particles, the tin source material includes tin powder, and the binder includes polyvinylidene fluoride.

5. The preparation method according to claim 1, characterized in that, The temperature of the first sintering is 150-250℃, and the temperature of the second sintering is 300-500℃.

6. Modified lithium titanate prepared by the preparation method according to any one of claims 1-5.

7. A negative electrode material, characterized in that, It includes the modified lithium titanate as described in claim 6, as well as a binder and a conductive agent.

8. A negative electrode sheet, characterized in that, It includes a current collector and the negative electrode material of claim 7 coated on the surface of the current collector.

9. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode as described in claim 8, a separator, and an electrolyte.

10. An electrical appliance, characterized in that, The device includes the lithium-ion battery of claim 9, wherein the lithium-ion battery provides electrical energy to the electrical device.