Coated modified cathode material, method for preparing the same, and lithium ion battery

Abstract

The application discloses a kind of co-coated modified positive electrode materials, its preparation method and lithium ion battery, co-coated modified positive electrode materials can be used to make lithium ion battery, including positive electrode material matrix and the coating layer of coating in the surface of positive electrode material matrix, coating layer includes MB2O4, M is at least one in Sr and Co;Preparation method is as follows: (1) positive electrode material matrix and coating agent are mixed, and mixed material is obtained;(2) mixed material is calcined under the condition of oxygen inlet for a set time.The surface of the positive electrode material of the application is stable, which is conducive to alleviating the phenomenon that the surface of the positive electrode material is eroded by electrolyte, improves the electrochemical performance of the positive electrode material, the preparation method is simple, easy to operate, the reaction condition is relatively mild, the preparation energy consumption and cost are relatively low, and it is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of cathode materials for lithium-ion batteries, specifically to a co-coated modified cathode material, its preparation method, and a lithium-ion battery using the cathode material. Background Technology

[0002] Lithium-ion batteries are now widely used in 3C, EV and energy storage fields. Due to their advantages such as high energy density, high operating voltage, long cycle time and small size, lithium-ion batteries have great advantages over nickel-metal hydride batteries and fuel cells in terms of application, and have become an indispensable functional application in people's lives today.

[0003] The cathode material is a crucial component of lithium-ion batteries, and its performance determines the final performance of the battery. Currently, with the increasing demand for high energy density in lithium-ion batteries, high-nickel ternary cathode materials have become the preferred choice. However, while high-nickel ternary materials offer the advantage of high energy density, their surface structure is unstable during cycling. The electrolyte easily corrodes the material surface, leading to surface structure degradation and a transformation into the rock salt phase. This results in adverse effects such as rapid energy decay, increased impedance, and reduced cycle life.

[0004] Existing technologies generally employ coating processes to improve the aforementioned problems. Coating refers to forming a coating layer on the surface of high-nickel ternary materials. This method not only reduces residual lithium on the surface but also isolates the surface of the high-nickel ternary material from the electrolyte, preventing contact between the two and thus further improving the electrochemical performance of the high-nickel material. Some studies have shown that coating layers containing boron (B) have good effects on high-nickel ternary materials. For example, CN115440952A discloses a technical solution for sintering and coating the surface of ternary cathode materials using boron-containing substances LiBO2, Li2B4O7, Li3BO3, and H3BO3. The coating layer formed by this solution contains LiBO2 and Li2B4O7, which can effectively reduce the impedance of lithium ion transmission at grain boundaries, thereby synergistically improving the efficiency of lithium ion insertion and extraction, and thus effectively improving the stability of the ternary cathode material. Another example is CN114079043A, which discloses a dual-coating layer structure of lithium tungsten oxide and lithium boron oxide layers to improve the high-temperature cycle performance of lithium-ion batteries. However, a single coating layer containing boron has limited effect on improving high-temperature cycling performance, while the dual coating layers of lithium tungsten oxide and lithium boron oxide are independent of each other, with uneven composition of the coating structure, making it difficult to exert synergistic advantages and maximize the effect of the coating layer on improving battery performance. Summary of the Invention

[0005] This invention provides a co-coated modified cathode material and its preparation method, which solves the technical problems of limited improvement effect on high-temperature cycling performance and non-uniform composition of the coating layer in existing cathode materials.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A co-coated modified cathode material includes a cathode material matrix and a coating layer covering the surface of the cathode material matrix, wherein the coating layer includes MB2O4, and M is at least one of Sr and Co.

[0008] This invention introduces another specific coating element M into the coating layer based on the conventional boron-containing coating process. A compound containing element M with a low decomposition temperature is selected and reacts synergistically with boric acid at low temperature, retaining the effects of both M and B to form an MB2O4 coating layer. This coating layer has high mechanical strength, protects the particles, helps alleviate the corrosion of the cathode material surface by the electrolyte, improves cycle performance, and has a uniform composition, maximizing the synergistic advantages of each element. This makes the cathode material, especially the high-nickel ternary cathode material, more stable, significantly improving the electrochemical performance of the cathode material in many ways.

[0009] As a further preferred embodiment of the above technical solution, the mass of the coating layer is 1% to 4% of the total mass of the co-coated modified cathode material. If the mass ratio of the coating layer is too low, it will not be able to effectively protect the cathode material; if the mass ratio of the coating layer is too high, it will increase the possibility of unreacted original substances remaining, thereby affecting the electrochemical performance of the cathode material.

[0010] As a further preferred embodiment of the above technical solution, the chemical formula of the positive electrode material matrix is ​​Li. a Ni x Mn y Co z M' b O2, wherein element M' is one or more of Al, Ti, Mg, Ba, Ca, Zr, Ta, Nb, and Mo, 0.9≤a≤1.1, 0≤b≤0.1, 0.5≤x≤1.0, 0≤y≤0.5, 0≤z≤0.5, and x+y+z+b=1. Because the surface structure of high-nickel ternary cathode materials is unstable during cycling, the electrolyte easily corrodes the material surface, leading to rapid energy decay, increased impedance, and reduced cycle life. Therefore, the coating layer of this invention has a more significant performance improvement effect on high-nickel ternary cathode materials compared to other cathode materials.

[0011] Based on the same technical concept, the present invention also provides a method for preparing the above-mentioned co-coated modified cathode material, comprising the following steps:

[0012] (1) The positive electrode material matrix and the coating agent are mixed to obtain a mixed material, wherein the coating agent includes boric acid and a compound containing element M;

[0013] (2) The mixed material is calcined at 280~320°C for a set time under the condition of oxygen introduction to obtain the co-coated modified cathode material.

[0014] As a further preferred embodiment of the above technical solution, the decomposition temperature of the coating agent is below 400°C. The decomposition temperature of the coating agent (the temperature at which the compound begins to decompose during heating under atmospheric pressure) is one of the important factors affecting whether the MB2O4 coating layer can be formed. If the decomposition temperature of the coating agent is too high, it will increase the difficulty of forming the MB2O4 coating layer and fail to achieve the desired protective effect on the cathode material.

[0015] As a further preferred embodiment of the above technical solution, the compound containing element M includes at least one of strontium acetate and cobalt oxalate.

[0016] As a further preferred embodiment of the above technical solution, the molar ratio of M to B in the coating agent is (0.1~1):2; even more preferably, the molar ratio of M to B in the coating agent is (0.1~0.5):2.

[0017] As a further preferred embodiment of the above technical solution, the roasting temperature in step (2) is 300℃ and the roasting time is 4~12h.

[0018] As a further preferred embodiment of the above technical solution, the oxygen flow rate in step (2) is 10~60 mL / min.

[0019] Based on the same technical concept, the present invention also provides a lithium-ion battery, wherein the positive electrode material of the lithium-ion battery is the co-coated modified positive electrode material described in the above technical solution or the co-coated modified positive electrode material prepared by the preparation method described in the above technical solution.

[0020] Compared with the prior art, the advantages of the present invention are as follows:

[0021] (1) This invention introduces another specific coating element M on the basis of the B-element coating layer of the cathode material. On the one hand, it can ensure the capacity improvement effect after the B-element coating. On the other hand, the MB2O4 coating layer formed on this basis has high mechanical strength, which can effectively protect the particles, alleviate the breakage of the particles during the charging and discharging process, improve the cycle performance, maximize the synergistic advantages of each element, make the cathode material surface more stable, help alleviate the phenomenon of the cathode material surface being eroded by the electrolyte, and improve the electrochemical performance of the cathode material, especially the high temperature cycle performance.

[0022] (2) The preparation method of the co-coated modified cathode material of the present invention preferably uses two coating raw materials that are decomposable at low temperature. On the other hand, the calcination temperature during the coating process is designed to be around 300°C, so as to ensure the smooth preparation of cathode material with a coating layer of specific components. At the same time, the preparation method of the present invention has simple steps, is easy to operate, and is easy to implement. Moreover, the reaction conditions are relatively mild, and the preparation energy consumption and cost are low, making it suitable for large-scale industrial production. Attached Figure Description

[0023] Figure 1 The image shows a comparison of the XRD patterns of the co-coated modified cathode material of Example 1 and the cathode material of Comparative Example 1.

[0024] Figure 2 The XRD patterns are shown in the comparison diagrams of the co-coated modified cathode material of Example 2 and the cathode material of Comparative Example 1.

[0025] Figure 3 The XRD pattern is a comparison of the co-coated modified cathode material of Example 3 and the cathode material of Comparative Example 1.

[0026] Figure 4 The image shows an XFE-SEM comparison of the cathode material of Comparative Example 1 with the co-coated modified cathode materials of Examples 1, 2, and 3. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments.

[0028] Example 1

[0029] The co-coated modified cathode material of this embodiment includes a cathode material substrate and a coating layer coated on the surface of the cathode material substrate. The coating layer has the chemical formula SrB₂O₄, and the cathode material substrate is a high-nickel ternary cathode material with the chemical formula LiNi. 0.9 Mn 0.05 Co 0.04 Y 0.01 O2, the mass of the coating layer is 2% of the mass of the co-coated modified cathode material. The XRD characterization comparison diagrams of the co-coated modified cathode material in this embodiment and the cathode material of Comparative Example 1 are shown below. Figure 1 As shown, combined with Figure 1 As can be seen from the XRD PDF standard card, the main component of the coating material of the co-coated modified cathode material in this embodiment is SrB2O4.

[0030] The preparation method of the co-coated modified cathode material in this embodiment includes the following steps:

[0031] (1) Take 500g of positive electrode material matrix, 2.86g of boric acid powder and 1.17g of strontium acetate powder, add them to a blender and mix them mechanically to obtain a mixed material.

[0032] (2) Place the mixed materials into a mortar, place the mortar in a box furnace, and heat it to 300°C at a rate of 1°C / min under the condition of oxygen introduction (oxygen introduction flow rate is 60ml / min) and maintain it for 8 hours.

[0033] (3) When the temperature of the box furnace naturally cools down to below 150°C, take out the material and pass it through a 300-mesh sieve to obtain the co-coated modified cathode material of this embodiment.

[0034] The FE-SEM comparison images of the cathode material of Comparative Example 1 and the co-coated modified cathode materials of Examples 1, 2, and 3 are shown below. Figure 4 As shown, in Figure 4 As can be observed, the co-coated modified cathode material particles in this embodiment have obvious coating material on their surface. This is because, at a certain temperature, strontium acetate can react with boric acid in the following way: Sr(C2H3O2)2 + 2xH3BO3 → SrB 2x O 3x+1 +H2O+CO2.

[0035] The co-coated modified positive electrode material of this embodiment was coated onto the positive electrode current collector aluminum foil, with lithium metal as the negative electrode and lithium hexafluorophosphate as the electrolyte. A separator was added, and the coin cell was assembled. The electrical performance of the coin cell was tested at 25°C using a Blue Electric testing system. The results are shown in Table 1. The results show that at 3.0-4.3V, the coin cell made with the co-coated modified positive electrode material of this embodiment has an initial discharge capacity of 218.1 mAh / g. After 50 high-temperature cycles, the capacity retention rate is 95.5%. The results prove that after the positive electrode material is coated with SrB2O4, the coating layer has a protective effect on the surface of the positive electrode material and can improve the cycle performance of the positive electrode material.

[0036] Example 2

[0037] The co-coated modified cathode material of this embodiment includes a cathode material substrate and a coating layer coated on the surface of the cathode material substrate. The coating layer has the chemical formula SrB₂O₄, and the cathode material substrate is a high-nickel ternary cathode material with the chemical formula LiNi. 0.9 Mn 0.05 Co 0.04 Y 0.01 O2, the mass of the coating layer is 3% of the mass of the co-coated modified cathode material. The XRD characterization comparison diagrams of the co-coated modified cathode material in this embodiment and the cathode material of Comparative Example 1 are shown below. Figure 2 As shown, combined with Figure 2 As can be seen from the XRD PDF standard card, the main component of the coating material of the co-coated modified cathode material in this embodiment is CoB2O4.

[0038] The preparation method of the co-coated modified cathode material in this embodiment includes the following steps:

[0039] (1) Take 500g of positive electrode material matrix, 2.86g of boric acid powder and 1.55g of cobalt oxalate powder, add them to a blender and mix them mechanically to obtain a mixed material.

[0040] (2) Place the mixed materials into a mortar, place the mortar in a box furnace, and heat it to 320°C at a rate of 1°C / min under the condition of oxygen introduction (oxygen introduction flow rate is 60ml / min) and maintain it for 4 hours.

[0041] (3) When the temperature of the box furnace naturally cools down to below 150°C, take out the material and pass it through a 300-mesh sieve to obtain the co-coated modified cathode material of this embodiment.

[0042] exist Figure 4 As can be observed, the surface of the co-coated modified cathode material particles in this embodiment has obvious coating material. This is because, at a certain temperature, cobalt oxalate can react with boric acid in the following way: CoC2O4 + H3BO3 → CoB2O4 + H2O + CO2.

[0043] The co-coated modified positive electrode material of this embodiment was coated onto the positive electrode current collector aluminum foil, with lithium metal as the negative electrode and lithium hexafluorophosphate as the electrolyte. A separator was added, and the coin cell was assembled. The electrical performance of the coin cell was tested at 25°C using a Blue Electric testing system. The results are shown in Table 1. The results show that at 3.0-4.3V, the coin cell made with the co-coated modified positive electrode material of this embodiment has an initial discharge capacity of 218.6 mAh / g. After 50 high-temperature cycles, the capacity retention rate is 95.3%. The results prove that after the positive electrode material is coated with a CoB2O4 coating layer, the coating layer has a protective effect on the surface of the positive electrode material and can improve the cycle performance of the positive electrode material.

[0044] Example 3

[0045] The co-coated modified cathode material of this embodiment includes a cathode material matrix and a coating layer coated on the surface of the cathode material matrix. The coating layer includes SrB₂O₄ and CoB₂O₄. The cathode material matrix is ​​selected as a high-nickel ternary cathode material with the chemical formula LiNi. 0.9 Mn 0.05 Co 0.04 Y 0.01 O2, the mass of the coating layer is 2% of the mass of the co-coated modified cathode material. The XRD characterization comparison diagrams of the co-coated modified cathode material in this embodiment and the cathode material of Comparative Example 1 are shown below. Figure 3 As shown, combined with Figure 3As can be seen from the XRDpdf standard card, the main components of the coating material of the co-coated modified cathode material in this embodiment are SrB2O4 and CoB2O4.

[0046] The preparation method of the co-coated modified cathode material in this embodiment includes the following steps:

[0047] (1) Take 500g of positive electrode material matrix, 2.86g of boric acid powder, 0.59g of strontium acetate powder and 0.78g of cobalt oxalate powder, add them to a blender and mechanically mix them to obtain a mixed material.

[0048] (2) Place the mixed materials into a mortar, place the mortar in a box furnace, and heat it to 280°C at a rate of 1°C / min under the condition of oxygen introduction (oxygen introduction flow rate is 60ml / min) and maintain it for 12 hours.

[0049] (3) When the temperature of the box furnace naturally cools down to below 150°C, take out the material and pass it through a 300-mesh sieve to obtain the co-coated modified cathode material of this embodiment.

[0050] exist Figure 4 As can be observed, the surface of the co-coated modified cathode material particles in this embodiment has obvious coating material, because strontium acetate and cobalt oxalate can react with boric acid at a certain temperature.

[0051] The co-coated modified positive electrode material of this embodiment was coated onto the positive electrode current collector aluminum foil, with lithium metal as the negative electrode and lithium hexafluorophosphate as the electrolyte. A separator was added, and the coin cell was assembled. The electrical performance of the coin cell was tested at 25°C using a Blue Electric testing system. The results are shown in Table 1. The results show that at 3.0-4.3V, the coin cell made with the co-coated modified positive electrode material of this embodiment has an initial discharge capacity of 220.7 mAh / g. After 50 high-temperature cycles, the capacity retention rate is 96.0%. The results prove that after the positive electrode material is coated with SrB2O4 and CoB2O4 coating layers, the coating layer has a protective effect on the surface of the positive electrode material and can improve the cycle performance of the positive electrode material.

[0052] Comparative Example 1

[0053] The preparation method of the cathode material in this comparative example includes the following steps:

[0054] (1) Take 500 grams of positive electrode material substrate (same as in Example 1), put it into a mortar, place the mortar in a box furnace, and heat it to 300°C at a rate of 1°C / min under the condition of oxygen introduction (oxygen introduction flow rate is 60 ml / min) and keep it for 8 hours.

[0055] (2) When the temperature of the box furnace naturally cools down to below 150°C, take out the material and pass it through a 300-mesh sieve to obtain the positive electrode material of this comparative example.

[0056] XRD tests were performed on the cathode material of this comparative example, and the results are shown below. Figure 1-3 .

[0057] like Figure 4 As shown, the surface of the cathode material particles in this comparative example is clean and smooth, without any coating material.

[0058] The positive electrode material of this comparative example was coated onto the positive electrode current collector aluminum foil, and lithium metal was used as the negative electrode. Lithium hexafluorophosphate was used as the electrolyte, a separator was added, and the coin cell was assembled. The electrical performance of the coin cell was tested at 25°C using the Blue Electric Test System. The results are shown in Table 1. The results show that at 3.0-4.3V, the coin cell made with the positive electrode material of this comparative example has an initial discharge capacity of 213.3mAh / g, and after 50 high-temperature cycles, the capacity retention rate is 84.1%.

[0059] Comparative Example 2

[0060] The preparation method of the cathode material in this comparative example includes the following steps:

[0061] (1) Take 500g of positive electrode material matrix (same as in Example 1) and 2.86g of boric acid powder, add them to a blender and mechanically mix them to obtain a mixed material.

[0062] (2) Place the mixed materials into a mortar, place the mortar in a box furnace, and heat to 300°C at a heating rate of 1°C / min under the condition of oxygen introduction (oxygen flow rate of 60ml / min) and maintain for 8 hours.

[0063] (3) When the temperature of the box furnace naturally cools down to below 150°C, take out the material and pass it through a 300-mesh sieve to obtain the positive electrode material of this comparative example.

[0064] The positive electrode material of this comparative example was coated onto the positive electrode current collector aluminum foil, and lithium metal was used as the negative electrode. Lithium hexafluorophosphate was used as the electrolyte, a separator was added, and the coin cell was assembled. The electrical performance of the coin cell was tested at 25°C using the Blue Electric Test System. The results are shown in Table 1. The results show that at 3.0-4.3V, the coin cell made with the positive electrode material of this comparative example has an initial discharge capacity of 220.5mAh / g, and after 50 high-temperature cycles, the capacity retention rate is 94.2%.

[0065] Comparative Example 3

[0066] The preparation method of the cathode material in this comparative example includes the following steps:

[0067] (1) Take 500g of positive electrode material matrix (same as in Example 1) and 1.17g of strontium acetate powder, add them to a blender and mechanically mix them to obtain a mixed material.

[0068] (2) Place the mixed materials into a mortar, place the mortar in a box furnace, and heat to 300°C at a heating rate of 1°C / min under the condition of oxygen introduction (oxygen flow rate of 60ml / min) and maintain for 8 hours.

[0069] (3) When the temperature of the box furnace naturally cools down to below 150°C, take out the material and pass it through a 300-mesh sieve to obtain the positive electrode material of this comparative example.

[0070] The positive electrode material of this comparative example was coated onto the positive electrode current collector aluminum foil, and lithium metal was used as the negative electrode. Lithium hexafluorophosphate was used as the electrolyte, a separator was added, and the coin cell was assembled. The electrical performance of the coin cell was tested at 25°C using the Blue Electric Test System. The results are shown in Table 1. The results show that at 3.0-4.3V, the coin cell made with the positive electrode material of this comparative example has an initial discharge capacity of 215.3mAh / g, and after 50 high-temperature cycles, the capacity retention rate is 95.1%.

[0071] Comparative Example 4

[0072] The preparation method of the cathode material in this comparative example includes the following steps:

[0073] (1) Take 500g of positive electrode material matrix (same as in Example 1) and 1.55g of cobalt oxalate powder, add them to a blender and mechanically mix them to obtain a mixed material.

[0074] (2) Place the mixed materials into a mortar, place the mortar in a box furnace, and heat to 300°C at a heating rate of 1°C / min under the condition of oxygen introduction (oxygen flow rate of 60ml / min) and maintain for 8 hours.

[0075] (3) When the temperature of the box furnace naturally cools down to below 150°C, take out the material and pass it through a 300-mesh sieve to obtain the positive electrode material of this comparative example.

[0076] The positive electrode material of this comparative example was coated onto the positive electrode current collector aluminum foil, and lithium metal was used as the negative electrode. Lithium hexafluorophosphate was used as the electrolyte, a separator was added, and the coin cell was assembled. The electrical performance of the coin cell was tested at 25°C using the Blue Electric Test System. The results are shown in Table 1. The results show that at 3.0-4.3V, the coin cell made with the positive electrode material of this comparative example has an initial discharge capacity of 216.5mAh / g, and after 50 high-temperature cycles, the capacity retention rate is 94.8%.

[0077] Comparative Example 5

[0078] The preparation method of the cathode material in this comparative example includes the following steps:

[0079] (1) Take 500g of positive electrode material matrix (same as in Example 1), 2.86g of boric acid powder, 0.59g of strontium acetate powder and 0.78g of cobalt oxalate powder, add them to a blender and mechanically mix them to obtain a mixed material.

[0080] (2) Place the mixed materials into a mortar, place the mortar in a box furnace, and heat to 200°C at a rate of 1°C / min under the condition of oxygen introduction (oxygen flow rate of 60ml / min) and maintain for 8 hours.

[0081] (3) When the temperature of the box furnace naturally cools down to below 150°C, take out the material and pass it through a 300-mesh sieve to obtain the positive electrode material of this comparative example.

[0082] The positive electrode material of this comparative example was coated onto the positive electrode current collector aluminum foil, and lithium metal was used as the negative electrode. Lithium hexafluorophosphate was used as the electrolyte, a separator was added, and the coin cell was assembled. The electrical performance of the coin cell was tested at 25°C using the Blue Electric Test System. The results are shown in Table 1. The results show that at 3.0-4.3V, the coin cell made with the positive electrode material of this comparative example has an initial discharge capacity of 211.6 mAh / g, and after 50 high-temperature cycles, the capacity retention rate is 92.1%.

[0083] Comparative Example 6

[0084] The preparation method of the cathode material in this comparative example includes the following steps:

[0085] (1) Take 500g of positive electrode material matrix (same as in Example 1), 2.86g of boric acid powder, 0.59g of strontium acetate powder and 0.78g of cobalt oxalate powder, add them to a blender and mechanically mix them to obtain a mixed material.

[0086] (2) Place the mixed materials into a mortar, place the mortar in a box furnace, and heat to 400°C at a rate of 1°C / min under the condition of oxygen introduction (oxygen flow rate of 60ml / min) and maintain for 8 hours.

[0087] (3) When the temperature of the box furnace naturally cools down to below 150°C, take out the material and pass it through a 300-mesh sieve to obtain the positive electrode material of this comparative example.

[0088] The positive electrode material of this comparative example was coated onto the positive electrode current collector aluminum foil, and lithium metal was used as the negative electrode. Lithium hexafluorophosphate was used as the electrolyte, a separator was added, and the coin cell was assembled. The electrical performance of the coin cell was tested at 25°C using the Blue Electric Test System. The results are shown in Table 1. The results show that at 3.0-4.3V, the coin cell made with the positive electrode material of this comparative example has an initial discharge capacity of 213.0 mAh / g, and after 50 high-temperature cycles, the capacity retention rate is 93.0%.

[0089] Comparative Example 7

[0090] The preparation method of the cathode material in this comparative example includes the following steps:

[0091] (1) Take 500g of positive electrode material matrix (same as in Example 1), 2.86g of boric acid powder, 0.42g of strontium carbonate powder and 0.39g of cobalt hydroxide powder, add them to a blender and mechanically mix them to obtain a mixed material.

[0092] (2) Place the mixed materials into a mortar, place the mortar in a box furnace, and heat to 300°C at a heating rate of 1°C / min under the condition of oxygen introduction (oxygen flow rate of 60ml / min) and maintain for 8 hours.

[0093] (3) When the temperature of the box furnace naturally cools down to below 150°C, take out the material and pass it through a 300-mesh sieve to obtain the positive electrode material of this comparative example.

[0094] The positive electrode material of this comparative example was coated onto the positive electrode current collector aluminum foil, and lithium metal was used as the negative electrode. Lithium hexafluorophosphate was used as the electrolyte, a separator was added, and the coin cell was assembled. The electrical performance of the coin cell was tested at 25°C using the Blue Electric Test System. The results are shown in Table 1. The results show that at 3.0-4.3V, the coin cell made with the positive electrode material of this comparative example has an initial discharge capacity of 208.3mAh / g, and after 50 high-temperature cycles, the capacity retention rate is 86.6%.

[0095] Table 1. Performance test results of batteries made from the cathode materials of each embodiment and comparative example.

[0096] B / ppm Sr / ppm Co / ppm Coating temperature / ℃ Discharge capacity (mAh / g) High temperature cycling retention rate / % Example 1 1000 1000 / 300 218.1 95.5 Example 2 1000 / 1000 320 218.6 95.3 Example 3 1000 500 500 280 220.7 96.0 Comparative Example 1 / / / 300 213.3 84.1 Comparative Example 2 1000 / / 300 220.5 94.2 Comparative Example 3 / 1000 / 300 215.3 95.1 Comparative Example 4 / / 1000 300 216.5 94.8 Comparative Example 5 1000 500 500 200 211.6 92.1 Comparative Example 6 1000 500 500 400 213.0 93.0 Comparative Example 7 1000 500 500 300 208.3 86.6

[0097] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and modifications obtained without departing from the inventive concept should also be considered within the scope of protection of the present invention.

Claims

1. A co-coated modified cathode material, characterized in that, It includes a positive electrode material matrix and a coating layer covering the surface of the positive electrode material matrix, wherein the coating layer includes MB2O4, and M is at least one of Sr and Co.

2. The co-coated modified cathode material according to claim 1, characterized in that, The mass of the coating layer is 1% to 4% of the total mass of the co-coated modified cathode material.

3. The co-coated modified cathode material according to claim 1 or 2, characterized in that, The chemical formula of the positive electrode material matrix is ​​Li a Ni x Mn y Co z M' b O2, wherein element M' is one or more of Al, Ti, Mg, Ba, Ca, Zr, Ta, Nb, and Mo, 0.9≤a≤1.1, 0≤b≤0.1, 0.5≤x≤1.0, 0≤y≤0.5, 0≤z≤0.5, and x+y+z+b=1.

4. A method for preparing the co-coated modified cathode material according to any one of claims 1-3, characterized in that, Includes the following steps: (1) The positive electrode material matrix and the coating agent are mixed to obtain a mixed material, wherein the coating agent includes boric acid and a compound containing element M; (2) The mixed material is calcined at 280~320°C for a set time under the condition of oxygen introduction to obtain the co-coated modified cathode material.

5. The method for preparing the co-coated modified cathode material according to claim 4, characterized in that, The decomposition temperature of the coating agent is below 400°C.

6. The method for preparing the co-coated modified cathode material according to claim 5, characterized in that, The compound containing element M includes at least one of strontium acetate and cobalt oxalate.

7. The method for preparing the co-coated modified cathode material according to claim 4, characterized in that, The molar ratio of M to B in the coating agent is (0.1~1):

2.

8. The method for preparing the co-coated modified cathode material according to any one of claims 4-7, characterized in that, The roasting time in step (2) is 4~12h.

9. A lithium-ion battery, characterized in that, The positive electrode material of the lithium-ion battery is the co-coated modified positive electrode material according to any one of claims 1-3 or the co-coated modified positive electrode material prepared by the preparation method according to any one of claims 4-8.

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