Application of soluble cyclotriphosphates in lithium ion battery cathode materials, polycrystalline ternary cathode material and preparation method thereof
By using soluble cyclic trimetaphosphate as a grain boundary binder in lithium-ion battery cathode materials, the problems of low ionic conductivity and high cost of binders in existing technologies have been solved, achieving high cycle stability and improved rate performance of the material, making it suitable for industrial applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CENT SOUTH UNIV
- Filing Date
- 2025-01-03
- Publication Date
- 2026-06-16
AI Technical Summary
Existing lithium-ion battery cathode materials suffer from low binder ion conductivity or high production costs, making it difficult to balance the material's cycle performance and rate performance. Existing modification methods are also difficult to apply industrially.
Soluble cyclic trimetaphosphate is used as a grain boundary binder and is uniformly coated on the surface of the ternary cathode material precursor through a rotary vacuum evaporation process. It is then sintered with lithium salt at high temperature to generate fast ion conductor lithium phosphate and dopant oxide, which are embedded in the grain boundaries inside the polycrystalline ternary cathode material.
It improves the cycle stability and rate performance of polycrystalline ternary cathode materials, with excellent cycle performance, first discharge capacity of no less than 209 mAh/g, first coulombic efficiency of no less than 88.7%, and 1C capacity retention of more than 80%, making it suitable for industrial applications.
Smart Images
Figure CN119994063B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion batteries, and particularly relates to the application of a soluble cyclic trimetaphosphate in lithium-ion battery cathode materials, polycrystalline ternary cathode materials and their preparation methods. Background Technology
[0002] Ternary cathode materials for lithium-ion batteries are widely used in various fields due to their high energy / power density, long cycle life, and good safety performance. As the energy density of ternary cathode materials gradually approaches their theoretical limit, a significant "seesaw" effect emerges between their cycle performance and rate performance. The key lies in the ternary cathode material / electrolyte interface. Increasing the interface area facilitates ion transport and improves the rate performance, but simultaneously exacerbates interfacial side reactions and deteriorates cycle performance; conversely, decreasing the interface area has the opposite effect.
[0003] To address the aforementioned issues, existing technologies generally employ elemental doping or surface coating methods to modify cathode materials. Elemental doping can suppress irreversible phase transitions under high voltage and widen the lithium layer spacing, while surface coating suppresses side reactions at the material / electrolyte interface and lowers the ion migration barrier. However, both methods face the challenge of balancing energy density and cycle / rate performance. Some researchers have proposed using cobalt-based binders to improve the structural stability of the material, but cobalt-based binders have low ionic conductivity, which is detrimental to the material's rate performance. Other researchers have proposed using thin-film deposition technology to embed lithium phosphate into secondary particles, but the binders obtained by this method are usually amorphous structures, exhibiting poor compatibility with ternary cathode materials. Furthermore, this method is costly and has stringent process requirements. In summary, existing binders applicable to battery cathode materials either have low ionic conductivity or high production costs, making industrial application difficult. Summary of the Invention
[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide an application of soluble cyclic tripolyphosphate in lithium-ion battery cathode materials, a polycrystalline ternary cathode material and its preparation method.
[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:
[0006] The application of a soluble cyclic trimetaphosphate in lithium-ion battery cathode materials, wherein the soluble cyclic trimetaphosphate is used as a grain boundary binder in the lithium-ion battery cathode material, and the soluble cyclic trimetaphosphate includes at least one of lithium cyclic trimetaphosphate, cobalt cyclic trimetaphosphate, manganese cyclic trimetaphosphate, magnesium cyclic trimetaphosphate, and aluminum cyclic trimetaphosphate.
[0007] In the above-described applications, preferably, the molar amount of the soluble cyclic trimetaphosphate accounts for 0.1%-1% of the molar amount of the lithium-ion battery cathode material.
[0008] As a general inventive concept, the present invention also provides a polycrystalline ternary cathode material, which uses a soluble cyclic trimetaphosphate as a grain boundary binder, wherein the soluble cyclic trimetaphosphate includes at least one of lithium trimetaphosphate, cobalt trimetaphosphate, manganese trimetaphosphate, magnesium trimetaphosphate, and aluminum trimetaphosphate.
[0009] As a general inventive concept, the present invention also provides a method for preparing the above-mentioned polycrystalline ternary cathode material, comprising the following steps:
[0010] (1) Add the ternary cathode material precursor to the soluble cyclic trimetaphosphate solution, mix evenly, and dry to obtain the cyclic trimetaphosphate-coated ternary cathode material precursor; the drying is carried out by a rotary vacuum evaporator, the temperature of the rotary vacuum evaporation is 45-70℃, the vacuum degree is 80-90KPa, and the drying time is 0.5h-10h; the rotary vacuum evaporation process can avoid the non-coated nucleation and growth of cyclic trimetaphosphate during the rapid evaporation of the aqueous solution, so that it is more evenly coated on the surface of the ternary precursor;
[0011] (2) The ternary cathode material precursor coated with cyclic trimetaphosphate is mixed with lithium salt and then subjected to high-temperature oxidation sintering treatment to obtain the polycrystalline ternary cathode material.
[0012] In the above preparation method, preferably, in step (1), the molar ratio of the soluble cyclic trimetaphosphate to the ternary cathode material precursor is (0.001-0.01):1.
[0013] In the above preparation method, preferably, in step (2), the molar ratio of the cyclic trimetaphosphate-coated ternary cathode material precursor to the lithium salt is 1:(1-1.1).
[0014] In the above preparation method, preferably, in step (2), the high-temperature oxidation sintering treatment is a segmented sintering treatment, first heating to 480-500℃ and holding for 4-6 hours, then heating to 720-900℃ and holding for 10-20 hours.
[0015] In the above preparation method, preferably, the lithium salt is lithium hydroxide, or a mixture of lithium hydroxide and lithium carbonate. To allow the molten lithium hydroxide (melting point 472°C) to carry the cyclic trimetaphosphate on the precursor surface into the particle interior, the lithium salt must contain lithium hydroxide. When the molar percentage of nickel in the ternary cathode material precursor is not higher than 60% of the transition metal ions, the lithium salt is preferably a mixture of lithium hydroxide and lithium carbonate, wherein the total amount of lithium hydroxide is greater than the amount consumed in the reaction with the cyclic trimetaphosphate; when the molar percentage of nickel in the ternary precursor is greater than 60% of the transition metal ions, the lithium salt is preferably lithium hydroxide.
[0016] In the above-described preparation method, preferably, the soluble cyclic trimetaphosphate includes at least one of cobalt cyclic trimetaphosphate, manganese cyclic trimetaphosphate, magnesium cyclic trimetaphosphate, and aluminum cyclic trimetaphosphate.
[0017] Furthermore, the cyclic trimetaphosphate is prepared using a sodium cyclic trimetaphosphate solution as a raw material, and the preparation method includes precipitation or ion exchange.
[0018] Precipitation method: 0.1M silver nitrate solution is added to sodium cyclotripolyphosphate solution of the same concentration, with a volume ratio of silver nitrate solution to sodium cyclotripolyphosphate solution of 3:1. After stirring for 24 hours, the mixture is filtered and washed to obtain silver cyclotripolyphosphate powder. The silver cyclotripolyphosphate powder is added to water to form a slurry, which is then slowly added to a metal chloride. After stirring for 1.5 hours, the silver chloride is filtered to obtain an aqueous solution containing soluble cyclotripolyphosphate. The metal chloride includes at least one of lithium chloride (LiCl), cobalt chloride (CoCl2), manganese chloride (MnCl2), magnesium chloride (MgCl2), and aluminum chloride (AlCl3). The chloride can exist in the form of anhydrous salt, salt containing water of crystallization, or solution. The molar amount of silver in the generated silver cyclotripolyphosphate is the same as the molar amount of chlorine in the chloride.
[0019] Ion exchange method: A sodium cyclic trimetaphosphate solution is converted into a cyclic trimetaphosphate solution by passing it through an IR220 / IRN77 strong acid ion exchange resin; the cyclic trimetaphosphate solution is then added to a metal carbonate or a metal hydroxide to obtain an aqueous solution containing a soluble cyclic trimetaphosphate; the metal carbonate includes at least one of lithium carbonate, cobalt carbonate, manganese carbonate, and magnesium carbonate; the metal hydroxide includes at least one of lithium hydroxide, cobalt hydroxide, magnesium hydroxide, and aluminum hydroxide; the metal carbonate and metal hydroxide can exist in anhydrous salt or salt containing water of crystallization.
[0020] Both the precipitation method and the ion exchange method can prepare cyclic trimetaphosphate solutions, but the ion exchange method is cheaper and easier to implement in continuous production. Therefore, the ion exchange method is preferred for preparing cyclic trimetaphosphate solutions.
[0021] Furthermore, the cyclic sodium trimetaphosphate solution is prepared by the following method: sodium dihydrogen phosphate is heated at 530-550℃ for 4-6 hours, the product is added to water and stirred, and the insoluble solid is filtered to obtain the cyclic sodium trimetaphosphate solution. In this process, increasing the reaction temperature or extending the sintering time will cause the cyclic sodium trimetaphosphate to transform into water-insoluble sodium metaphosphate, resulting in a decrease in the yield of the target product. Therefore, this process requires controlling the reaction temperature and time within a suitable range.
[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0023] (1) In this invention, cyclic trimetaphosphate is used as a grain boundary binder in the positive electrode material of lithium-ion batteries. Cyclic trimetaphosphate is an uncommon chemical, and its melting point is higher than that of lithium hydroxide. Therefore, molten lithium hydroxide can be used to carry the binder into the grain boundary inside the secondary particles. In addition, cyclic trimetaphosphate can react with lithium hydroxide to generate lithium phosphate and oxide. Among them, lithium phosphate, as a fast ion conductor, will reduce the influence of grain boundary binder on lithium ion transport, and oxide, as a dopant, can further improve the structural stability of the material.
[0024] (2) In this invention, soluble cyclic trimetaphosphate is used as a grain boundary binder in lithium-ion battery cathode materials. Soluble cyclic trimetaphosphate can easily achieve uniform coating on the surface of ternary precursors. During the sintering process, fast ion conductor lithium phosphate is embedded into the grain boundaries inside the secondary particles of polycrystalline ternary cathode materials. The binder can increase the critical internal stress generated by grain boundary cracks in ternary cathode materials and effectively improve the interfacial stability of materials, suppress the occurrence of interfacial side reactions, thereby improving the cycle stability of materials.
[0025] (3) In this invention, soluble cyclic trimetaphosphate is used as a grain boundary binder in the positive electrode material of lithium-ion batteries. Soluble cyclic trimetaphosphate grain boundary binder is a fast ion conductor, which can solve the problem that traditional modification methods cannot take into account both the cycle performance and rate performance of the material. The modification method is relatively simple to operate and is suitable for industrial application.
[0026] (4) In this invention, the byproducts of the reaction between lithium salt and grain boundary binders such as cobalt cyclotrimethphosphate, manganese cyclotrimethphosphate, magnesium cyclotrimethphosphate or aluminum cyclotrimethphosphate can also be used as dopants to further improve the structural stability of the material.
[0027] (5) The polycrystalline ternary cathode material prepared by the present invention has excellent cycle performance and rate performance. The initial discharge capacity at 0.1C is not less than 209mAh / g, the initial coulombic efficiency is not less than 88.7%, and the number of cycles exceeds 350 when the 1C capacity retention rate is 80%. Attached Figure Description
[0028] Figure 1 The image shows the XRD pattern of cyclic sodium trimetaphosphate prepared in Example 1 of this invention.
[0029] Figure 2 The image shows a TEM / EDS image of the ternary cathode material prepared in Example 1 of this invention.
[0030] Figure 3 The image shows the SEM / EDS image of the ternary cathode material prepared in Comparative Example 2 of this invention. Detailed Implementation
[0031] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.
[0032] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.
[0033] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.
[0034] The specific processes of precipitation and ion exchange methods involved in the following examples and comparative examples are as follows:
[0035] Aqueous solutions of soluble cyclic tripolyphosphate
[0036] (1) Cyclic sodium trimetaphosphate solution
[0037] Sodium dihydrogen phosphate was heated at 540°C for 5 hours. The reaction product was then added to water and stirred. The insoluble solid was filtered to obtain a solution of cyclic sodium tripolyphosphate.
[0038] (2) Methods for preparing cyclic metaphosphates
[0039] 1. Precipitation method
[0040] A 0.1M silver nitrate solution with a volume ratio of approximately 3:1 was added to a sodium cyclotrimetaphosphate solution of the same concentration. After stirring for 24 hours, the solution was filtered, washed, and dried to obtain silver cyclotrimetaphosphate powder. The silver cyclotrimetaphosphate powder was then mixed with a certain amount of water to form a slurry, which was slowly added to an equimolar amount of chloride. After stirring for 1.5 hours, the silver chloride was filtered to obtain an aqueous solution containing soluble cyclotrimetaphosphate.
[0041] 2. Ion exchange method
[0042] The sodium cyclic trimetaphosphate solution was converted into a cyclic trimetaphosphate solution by passing it through an IR220 / IRN77 strong acid ion exchange resin. The cyclic trimetaphosphate solution was then added to carbonate to obtain an aqueous solution containing soluble cyclic trimetaphosphate.
[0043] Example 1:
[0044] This embodiment relates to the application of cyclic lithium trimetaphosphate in lithium-ion battery cathode materials. The cyclic lithium trimetaphosphate is used as a grain boundary binder, and its molar ratio in the lithium-ion battery cathode material is about 0.5%.
[0045] This embodiment relates to a polycrystalline ternary cathode material containing a grain boundary binder, lithium cyclic trimetaphosphate, and its preparation method includes the following steps:
[0046] (1) After heating sodium dihydrogen phosphate at 540℃ for 5 hours, the reaction product was added to water and stirred. The insoluble solid was filtered to obtain a cyclic sodium trimetaphosphate solution (its XRD pattern is shown in Figure 1). Figure 1 (As shown). A 0.1M silver nitrate solution with a volume ratio of approximately 3:1 was added to a 0.1M sodium cyclotripolyphosphate solution. After stirring for 24 hours, the solution was filtered, washed, and dried to obtain silver cyclotripolyphosphate powder. The silver cyclotripolyphosphate powder was added to water to form a slurry, which was then slowly added to an equimolar amount of lithium chloride. After stirring for 1.5 hours, the silver chloride was filtered to obtain an aqueous solution containing soluble lithium cyclotripolyphosphate.
[0047] (2) Add Ni, a ternary cathode material precursor, to the aqueous solution containing soluble cyclic lithium trimetaphosphate prepared in step (1). 0.9 Co 0.05 Mn 0.05 The molar ratio of (OH)2, cyclic lithium trimetaphosphate, and the ternary cathode material precursor was 0.005:1. The mixture was dried for 8 hours using a rotary vacuum evaporator at 85 kPa and 50 °C to obtain Ni coated with cyclic lithium trimetaphosphate. 0.9 Co 0.05 Mn 0.05 (OH)2 precursor.
[0048] (3) The Ni coated with the cyclic lithium trimetaphosphate prepared in step (2) 0.9 Co 0.05 Mn 0.05 The (OH)₂ precursor was thoroughly mixed with lithium hydroxide at a molar ratio of 1.05:1 and then subjected to high-temperature oxidation sintering. The temperature was first raised to 480℃ and held for 5 hours, then raised to 720℃ and held for 15 hours to obtain a polycrystalline ternary cathode material. Its TEM / EDS image is shown below. Figure 2 As shown, from Figure 2 It can be seen that the lithium phosphate binder has fully penetrated into the interior of the secondary particles of the ternary material.
[0049] The prepared polycrystalline ternary cathode material was coated, rolled, cut into sheets, and assembled into batteries. The performance test results at 2.7-4.3V are shown in Table 1.
[0050] Comparative Example 1:
[0051] This comparative example uses only high-nickel ternary cathode material as a blank control for performance testing. The specific preparation process includes the following steps:
[0052] Ni 0.9 Co0.05 Mn 0.05 The (OH)2 precursor and lithium hydroxide were thoroughly mixed at a molar ratio of 1:1.05 and then subjected to high-temperature oxidation sintering treatment. The temperature was first raised to 480℃ and held for 5 hours, and then raised to 720℃ and held for 15 hours to obtain a high-nickel ternary cathode material.
[0053] The prepared high-nickel ternary cathode material was coated, rolled, cut into sheets, and assembled into batteries. The performance test results at 2.7-4.3V are shown in Table 1.
[0054] Comparative Example 2:
[0055] The preparation method of the polycrystalline ternary cathode material in this comparative example differs from that in Example 1 only in the amount of cyclic lithium trimetaphosphate added. In step (2) of this comparative example, the molar ratio of cyclic lithium trimetaphosphate to the ternary cathode material precursor is 0.02:1, and other processes and parameters are the same as in Example 1.
[0056] The SEM / EDS image of the polycrystalline ternary cathode material prepared in this comparative example is shown below. Figure 3 As shown in the figure, the binder exceeding the grain boundary volume of the ternary cathode material will be on the surface of the secondary particles, leading to the aggregation of the secondary particles.
[0057] The polycrystalline ternary cathode material prepared in this comparative example was coated, rolled, cut into sheets, and assembled into batteries. The performance test results at 2.7-4.3V are shown in Table 1.
[0058] Table 1: Performance test results of Example 1 and Comparative Examples 1-2
[0059]
[0060] As shown in Table 1, the polycrystalline ternary cathode material prepared in Example 1 exhibits significantly better electrochemical performance than that of Comparative Example 1. This indicates that the ternary cathode material prepared by wet in-situ coating of cyclic trimetaphosphate with a precursor, followed by thorough mixing with lithium salt and high-temperature oxidation sintering, can simultaneously improve both cycle performance and rate performance. It is also worth noting that the amount of cyclic trimetaphosphate coating should not exceed the volume of the grain boundaries within the polycrystalline ternary material; otherwise, excess binder will accumulate on the surface of the secondary particles, leading to particle agglomeration and consequently affecting the material's electrochemical performance.
[0061] Example 2:
[0062] The only difference between Example 2 and Example 1 is that the grain boundary binder is different. The grain boundary binder in this example is cobalt cyclotripolyphosphate, which is prepared by precipitation method. Other processes and parameters are exactly the same as in Example 1.
[0063] Example 3:
[0064] The only difference between Example 3 and Example 1 is that the grain boundary binder is different. The grain boundary binder in this example is cyclic manganese trimetaphosphate, which is prepared by ion exchange. The other processes and parameters are exactly the same as in Example 1.
[0065] Example 4:
[0066] The only difference between Example 4 and Example 1 is that the grain boundary binder is different. The grain boundary binder in this example is cyclic magnesium trimetaphosphate, which is prepared by precipitation method. Other processes and parameters are exactly the same as in Example 1.
[0067] Example 5:
[0068] The only difference between Example 5 and Example 1 is that the grain boundary binder is different. The grain boundary binder in this example is cyclic aluminum trimetaphosphate, which is prepared by ion exchange method. Other processes and parameters are exactly the same as in Example 1.
[0069] Comparative Example 3:
[0070] The difference between this comparative example and Example 2 is that the drying method in step (2) is different, and the rotary vacuum evaporator drying in step (2) is replaced by stirring drying.
[0071] The electrochemical performance of the polycrystalline ternary cathode materials prepared in Examples 2-5 and Comparative Example 3 is shown in Table 2.
[0072] Table 2: Performance test results of Examples 2-3 and Comparative Examples 3-4
[0073]
[0074] As shown in Table 2, the performance of the polycrystalline ternary cathode material prepared in the examples is significantly better than that of the comparative example in terms of electrochemical performance. Combining Table 1, a comparison between Examples 2-5 and Example 1 shows that the cycle performance of Examples 2-5 is significantly better than that of Example 1. This may be attributed to the fact that the byproducts of the reaction between the grain boundary binder and lithium salt used in Examples 2-5 can act as dopants, thereby improving the stability of the material. A comparison of the experimental data from Example 2 and Comparative Example 3 shows that cyclic trimetaphosphate, as a grain boundary binder, requires very high drying standards during the mixing process with the precursor material. The rotary vacuum evaporation process avoids the non-coating nucleation and growth of cyclic trimetaphosphate during rapid evaporation of the aqueous solution, allowing it to be more uniformly coated on the surface of the ternary precursor, ensuring the excellent performance of the prepared polycrystalline ternary cathode material. Conversely, conventional drying methods make it difficult to fully utilize the advantages of cyclic trimetaphosphate as a grain boundary binder, thus failing to effectively improve the material performance.
Claims
1. The application of a soluble cyclic trimetaphosphate in lithium-ion battery cathode materials, characterized in that, The soluble cyclic trimetaphosphate is used as a grain boundary binder in lithium-ion battery cathode materials. The soluble cyclic trimetaphosphate includes at least one of lithium trimetaphosphate, cobalt trimetaphosphate, manganese trimetaphosphate, magnesium trimetaphosphate, and aluminum trimetaphosphate. The application includes the following steps: adding a ternary cathode material precursor to a soluble cyclic trimetaphosphate solution, drying it using a rotary vacuum evaporator at a temperature of 45-70℃ and a vacuum degree of 80-90KPa for 0.5-10h, and then mixing it with lithium salt for high-temperature oxidation sintering treatment. The molar amount of the soluble cyclic trimetaphosphate accounts for 0.1%-1% of the molar amount of the lithium-ion battery cathode material.
2. A polycrystalline ternary cathode material, characterized in that, The specific application of using soluble cyclic trimetaphosphate as a grain boundary binder is as follows: a ternary cathode material precursor is added to a soluble cyclic trimetaphosphate solution and dried for 0.5-10 hours using a rotary vacuum evaporator at a temperature of 45-70℃ and a vacuum degree of 80-90KPa. Then, it is mixed with lithium salt and subjected to high-temperature oxidation sintering treatment. The molar amount of the soluble cyclic trimetaphosphate accounts for 0.1%-1% of the molar amount of the polycrystalline ternary cathode material. The soluble cyclic trimetaphosphate includes at least one of lithium cyclic trimetaphosphate, cobalt cyclic trimetaphosphate, manganese cyclic trimetaphosphate, magnesium cyclic trimetaphosphate, and aluminum cyclic trimetaphosphate.
3. A method for preparing the polycrystalline ternary cathode material as described in claim 2, characterized in that, Includes the following steps: (1) Add the ternary cathode material precursor to the soluble cyclic trimetaphosphate solution and mix evenly, then dry to obtain the cyclic trimetaphosphate-coated ternary cathode material precursor; wherein the drying is carried out by a rotary vacuum evaporator, the rotary vacuum evaporation temperature is 45-70℃, the vacuum degree is 80-90KPa, and the drying time is 0.5h-10h; (2) The ternary cathode material precursor coated with cyclic trimetaphosphate is mixed with lithium salt and then subjected to high-temperature oxidation sintering treatment to obtain the polycrystalline ternary cathode material.
4. The preparation method according to claim 3, characterized in that, In step (1), the molar ratio of the soluble cyclic trimetaphosphate to the ternary cathode material precursor is (0.001-0.01):
1.
5. The preparation method according to claim 3, characterized in that, In step (2), the molar ratio of the cyclic trimetaphosphate-coated ternary cathode material precursor to the lithium salt is 1:(1-1.1).
6. The preparation method according to claim 3, characterized in that, In step (2), the high-temperature oxidation sintering treatment is a segmented sintering treatment, first heating to 480-500℃ and holding for 4-6 hours, then heating to 720-900℃ and holding for 10-20 hours.
7. The preparation method according to claim 3, characterized in that, The lithium salt is lithium hydroxide, or a mixture of lithium hydroxide and lithium carbonate.
8. The preparation method according to claim 3, characterized in that, The soluble cyclic trimetaphosphate includes at least one of cobalt cyclic trimetaphosphate, manganese cyclic trimetaphosphate, magnesium cyclic trimetaphosphate, and aluminum cyclic trimetaphosphate.