Modified lithium-rich manganese-based positive electrode material, and preparation method therefor and use thereof

Abstract

A modified lithium-rich manganese-based positive electrode material, and a preparation method therefor and the use thereof. The modified lithium-rich manganese-based positive electrode material comprises a lithium-rich manganese-based positive electrode material, wherein the bulk phase of the lithium-rich manganese-based positive electrode material is doped with a high-valent transition metal element, and the surface phase of the lithium-rich manganese-based positive electrode material has a lithium metal compound coating layer and an oxygen vacancy. In the modified lithium-rich manganese-based positive electrode material, the doping with a bulk-phase high-valence transition metal element, the coating with a surface-phase lithium metal compound coating layer and the construction of an oxygen vacancy are conducted at the same time; and by means of the co-action of the three, the rate capability and the cycling performance of the lithium-rich manganese-based positive electrode material can be significantly improved, which is of great significance for the further commercialization of the lithium-rich manganese-based positive electrode material.

Description

A modified lithium-rich manganese-based cathode material, its preparation method and application Technical Field

[0001] This application relates to the field of energy battery materials technology, and in particular to a modified lithium-rich manganese cathode material, its preparation method, and its application. Background Technology

[0002] In recent years, lithium-rich manganese-based cathode materials have attracted attention from the market and numerous researchers due to their advantages such as high operating voltage (3.7–4.8V), ultra-high specific capacity (approximately 250mAh / g), and low cost (high manganese, low cobalt, or even cobalt-free), and may become the cathode material for next-generation commercial high-energy-density lithium batteries. The high capacity of lithium-rich manganese-based cathode materials comes from two aspects: the oxidation of transition metal ions in the low-voltage segment (<4.5V) and the redox reaction of lattice oxygen in Li₂MnO₃ in the high-voltage segment (≥4.5V). That is, lithium ions are released from the structure along with the oxidation and release of lattice oxygen.

[0003] It is worth noting that the lattice oxygen in the bulk phase of the material can undergo reversible redox reactions, while the lattice oxygen on the surface layer is highly reactive, and the redox reactions that occur during electrochemical cycling are irreversible. Irreversible oxygen release creates O and Li vacancies, causing the migration of transition metal ions, leading to lattice compaction and the formation of defective spinel structures. Continued cycling will transform these into disordered rock salt structures with no electrochemical activity. Furthermore, oxygen evolution exacerbates side reactions between the material and the electrolyte, resulting in the deposition of numerous complex byproducts such as Li₂CO₃ and LiF on the material surface, consuming a large amount of lithium ions. All of these factors contribute to increased surface impedance. In summary, while lithium-rich manganese-based cathode materials possess high energy density, they also suffer from problems such as rapid voltage decay, poor rate performance, and low capacity retention.

[0004] CN115924997A discloses a lanthanum-magnesium co-doped lithium-rich manganese-based cathode material and its preparation method. The lithium-rich manganese-based cathode material prepared by this method achieves uniform lanthanum-magnesium doping, effectively suppresses lithium-nickel cation mixing, stabilizes the layered structure, and reduces the erosion of electrolyte by-products.

[0005] CN116623295A discloses a modified cobalt-free single-crystal lithium-rich manganese-based cathode material co-doped with tantalum and zirconium and its preparation method. By mixing a lithium-rich manganese-based precursor with lithium hydroxide, tantalum pentoxide and zirconium oxide, and then ball milling it and calcining it, tantalum and zirconium co-doping is achieved, which effectively suppresses the irreversible decay of the first-cycle capacity and significantly improves the first coulombic efficiency.

[0006] CN116741963A discloses a lithium-rich manganese-based cathode material coated with metal fluoride and its preparation method. A certain amount of nickel source and fluorine source are added to anhydrous ethanol, and the lithium-rich manganese-based cathode material is slowly added and heated and stirred. After the material is dried and ground, it is then annealed and calcined to construct a metal fluoride coating layer, which effectively improves the interface between the cathode material and the electrolyte and achieves long-term cycle stability of the lithium-rich manganese-based cathode material at high / low rates.

[0007] However, the effects of single doping, coating, or structural regulation disclosed in the above-mentioned related technologies are relatively limited, and they cannot simultaneously achieve high rate performance and high cycle stability of lithium-rich manganese-based cathode materials. This results in performance shortcomings of lithium-rich manganese-based materials in practical applications, hindering market development.

[0008] Therefore, providing a lithium-rich manganese-based cathode material that significantly improves both the rate performance and cycle performance of lithium-rich manganese-based cathode materials is an urgent technical problem to be solved.

[0009] Summary of the Invention

[0010] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0011] This application provides a modified lithium-rich manganese-based cathode material, its preparation method, and its application. The modified lithium-rich manganese-based cathode material provided in this application simultaneously incorporates bulk high-valence transition metal doping, surface metal lithiation coating, and oxygen vacancy construction. The combined effect of these three factors significantly improves the rate performance and cycle performance of the lithium-rich manganese-based cathode material, which is of great significance for the further commercialization of lithium-rich manganese-based cathode materials.

[0012] In a first aspect, this application provides a modified lithium-rich manganese-based cathode material, the modified lithium-rich manganese-based cathode material comprising a lithium-rich manganese-based cathode material, wherein the bulk phase of the lithium-rich manganese-based cathode material is doped with a high-valence transition metal element, and the surface phase of the lithium-rich manganese-based cathode material has a metal lithide coating layer and oxygen vacancies.

[0013] In this application, "high valence" in "high-valence transition metal element" refers to the doped metal element having a valence state of pentavalent or hexavalent.

[0014] In this application, the high-valence transition metal elements doped into the bulk phase of the lithium-rich manganese-based cathode material enhance the covalent relationship between the transition metal and oxygen ions, improving the structural stability of the material. Moreover, the large atomic radius of the transition metal elements increases the interlayer spacing after doping into the bulk phase, promoting the rapid migration of lithium ions and thus improving the rate performance of the material. Secondly, the high-valence transition metal elements also form a lithium metal lithium oxide coating layer on the material surface during the doping process. This coating layer can effectively prevent electrolyte erosion, thereby improving the cycle stability of the material. At the same time, this application also constructs a large number of oxygen vacancies on the surface phase of the lithium-rich manganese-based cathode material, suppressing irreversible oxygen release from the material surface and solving the structural defects caused by irreversible oxygen release, thereby significantly improving the rate performance of the lithium-rich manganese-based cathode material.

[0015] Therefore, in the modified lithium-rich manganese-based cathode material provided in this application, the doping of high-valence metal elements, the coating of the metal lithium compound coating layer, and the construction of surface oxygen vacancies work together to significantly improve the electrochemical performance of the lithium-rich manganese-based cathode material.

[0016] In one embodiment, the high-valence transition metal element includes any one or a combination of at least two of niobium, molybdenum, tungsten, or tantalum.

[0017] In one embodiment, the lithium metal compound in the lithium metal compound coating layer includes any one or a combination of at least two of lithium niobate, lithium molybdate, lithium tungstate, or lithium tantalate.

[0018] Secondly, this application provides a method for preparing a modified lithium-rich manganese-based cathode material as described in the first aspect, the method comprising the following steps:

[0019] (1) After mixing lithium-rich manganese-based precursor, lithium source and high-valence transition metal source, lithiation reaction is carried out to obtain lithium-rich manganese-based cathode material with bulk doped high-valence transition metal elements and surface coated metal lithides.

[0020] (2) The lithium-rich manganese-based cathode material obtained in step (1) with high-valence transition metal elements in the bulk phase and metal lithium compounds in the surface phase is mixed with an ammonium acid compound and calcined to obtain the modified lithium-rich manganese-based cathode material.

[0021] This application provides a method for preparing modified lithium-rich manganese-based cathode materials. This method achieves doping, coating, and structural regulation of lithium-rich manganese-based cathode materials by introducing high-valence transition metal sources and acid amine compounds, thereby significantly improving the electrochemical performance of lithium-rich manganese-based cathode materials.

[0022] The high-valence transition metal source introduced in the preparation method provided in this application can, on the one hand, achieve doping of high-valence transition metal elements in the bulk phase of the cathode material; on the other hand, the high-valence transition metal elements can also react with the lithium source on the surface of the material during the reaction process, thereby forming a metal lithide coating layer on the surface phase of the cathode material.

[0023] In this application, the acid amine compound decomposes to produce reducing gas during the reaction with the lithium-rich manganese-based cathode material, thereby constructing oxygen vacancies on the surface of the lithium-rich manganese cathode material.

[0024] The preparation method provided in this application has the advantages of simple process, easy industrial production, and the ability to simultaneously achieve high rate performance and high cycle stability of lithium-rich manganese-based cathode materials.

[0025] In one embodiment, the lithium-rich manganese-based precursor comprises Ni x Co y Mn 1-x-y (OH)2 or Ni x Co y Mn 1-x-y Any one of CO3, where 0.4 ≥ x > 0.3 and y < 0.1.

[0026] In one embodiment, the lithium source includes lithium carbonate and / or lithium hydroxide.

[0027] In one embodiment, the high-valence transition metal source comprises a high-valence transition metal oxide.

[0028] In one embodiment, the high-valence transition metal oxide includes any one or a combination of at least two of niobium oxide, molybdenum oxide, tungsten oxide, or tantalum oxide.

[0029] In one embodiment, the ratio of the total molar amount of the transition metal elements in the lithium-rich manganese-based precursor and the transition metal elements in the high-valence transition metal oxide to the molar amount of lithium in the lithium source is 1:(1.3 to 1.6), for example, 1:1.3, 1:1.35, 1:1.4, 1:1.45, 1:1.5, 1:1.55 or 1:1.6, etc.

[0030] In this application, by adjusting the ratio of the total molar amount of metal elements in the lithium-rich manganese-based precursor and the high-valence transition metal oxide to the molar amount of lithium elements in the lithium source, the electrochemical performance of the material can be controlled within a certain range. If the molar ratio is too small, there will be too much lithium source, which may lead to the formation of too much irreversible phase Li2MnO3 and thus reduce the electrochemical performance. If the molar ratio is too large, there will be insufficient lithium source, resulting in too low capacity.

[0031] In one embodiment, based on the total molar amount of transition metal in the lithium-rich manganese-based precursor and the high-valence transition metal source described in step (1), the molar percentage of the high-valence transition metal element is 0.1% to 4%, for example, 0.1%, 0.4%, 0.7%, 1%, 1.3%, 1.6%, 1.9%, 2.2%, 2.5%, 2.8%, 3.1%, 3.4%, 3.7%, or 4%.

[0032] In this application, controlling the amount of high-valence transition metal elements added can maximize the electrochemical performance of lithium-rich manganese cathode materials. If the amount of high-valence transition metal elements added is too small, it will not be enough to expand the lithium interlayer spacing, thus failing to effectively promote the rapid migration of lithium ions; if the amount of high-valence transition metal elements added is too large, the high-valence transition metals may form an excessively thick and unevenly distributed lithium compound coating layer on the material surface, thereby leading to a decrease in electrochemical performance.

[0033] In one embodiment, the temperature of the lithiation reaction in step (1) is 750 to 1000°C, for example, 750°C, 800°C, 850°C, 900°C, 950°C or 1000°C.

[0034] In one embodiment, the lithiation reaction time in step (1) is 10 to 15 hours, for example, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours or 15 hours.

[0035] The lithiation reaction in this application can be achieved through a roasting process after mixing the raw materials.

[0036] In one embodiment, the mixture obtained by mixing is pre-calcined before the lithiation reaction in step (1).

[0037] In one embodiment, the preheating temperature in step (1) is 350 to 600°C, for example, 350°C, 400°C, 450°C, 500°C, 550°C or 600°C.

[0038] In one embodiment, the preheating time in step (1) is 4 to 6 hours, for example, 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours.

[0039] In this application, no specific limitation is made on the pre-firing equipment. The pre-firing equipment includes, but is not limited to, muffle furnaces or tube furnaces, and those skilled in the art can choose according to their needs.

[0040] In one embodiment, the ammonium acid compound in step (2) includes any one or a combination of at least two of ammonium carbonate, ammonium bicarbonate, ammonium oxalate, ammonium citrate, or ammonium tartrate.

[0041] In one embodiment, in step (2), based on the mass of the bulk doped high-valence transition metal element and the surface coated lithium-rich manganese-based cathode material obtained in step (1) being 100%, the amount of the ammonium acid compound added is 0.5% to 5%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%.

[0042] In this application, the electrochemical performance of the material can be optimized by adjusting the amount of ammonium acid compounds added in the reaction. If the amount of ammonium acid compounds added is too low, the amount of reducing gas produced is too small to enhance the structural stability by affecting the local Mn coordination environment, and the problem of irreversible oxygen release cannot be effectively alleviated. If the amount of ammonium acid compounds added is too large, resulting in too many oxygen vacancies and too high a amount of reducing gas produced, it may induce the migration of transition metal ions, leading to a phase transition between spinel and rock salt phases, thereby changing the structure of the cathode material, increasing the migration resistance of lithium ions, and reducing the electrochemical performance.

[0043] In one embodiment, the calcination temperature in step (2) is 200 to 500°C, for example, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C or 500°C.

[0044] In this application, adjusting the calcination temperature of the lithium-rich manganese-based cathode material pre-modified with transition metal oxides and mixed with acid amine compounds can effectively achieve the construction of oxygen vacancies. If the calcination temperature is too low, the acid amine compounds cannot be completely decomposed and thus cannot generate an appropriate amount of oxygen vacancies. If the calcination temperature is too high, it may affect the structure of the material.

[0045] In one embodiment, the calcination time in step (2) is 1 to 4 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours.

[0046] In one embodiment, the gas in the calcination atmosphere in step (2) includes at least one of compressed air, nitrogen, or an inert gas.

[0047] Thirdly, this application provides a cathode comprising the modified lithium-rich manganese-based cathode material as described in the first aspect.

[0048] Fourthly, this application provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode as described in the third aspect.

[0049] Compared with related technologies, this application has at least the following beneficial effects:

[0050] (1) The modified lithium-rich manganese-based cathode material provided in this application simultaneously has the doping of high-valence transition metal elements in the bulk phase, the coating of the surface phase metal lithiumide coating layer and the construction of oxygen vacancies. The three factors work together to significantly improve the rate performance and cycle performance of the lithium-rich manganese-based cathode material, which is of great significance for the further commercialization of lithium-rich manganese-based cathode materials.

[0051] (2) In preparing the modified lithium-rich manganese-based cathode material, this application introduces a high-valence transition metal source and acid amine compounds for synergistic modification, thereby achieving the effects of high-valence transition metal doping, metal lithium coating, and surface oxygen vacancy construction, which significantly improves the electrochemical performance of the lithium-rich manganese-based cathode material.

[0052] After reading and understanding the detailed description, other aspects can be understood. Detailed Implementation

[0053] To facilitate understanding of this application, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of this application.

[0054] Example 1

[0055] This embodiment provides a modified lithium-rich manganese-based cathode material, including a lithium-rich manganese-based cathode material, wherein the bulk phase of the lithium-rich manganese-based cathode material is doped with molybdenum, and the surface phase of the lithium-rich manganese-based cathode material has a lithium molybdate coating layer and constructed oxygen vacancies.

[0056] This embodiment describes the preparation of the modified lithium-rich manganese-based cathode material using a method that synergistically modifies lithium oxide and ammonium oxalate. The steps are as follows:

[0057] (1) Weigh Ni according to the following ratio: molybdenum accounts for 0.5% of the total molar amount of transition metal elements in the raw material and lithium is in a molar ratio of 1.45 to the total transition metal elements. 0.35 Co 0.05 Mn 0.6 (OH)2, molybdenum oxide and lithium carbonate were mixed evenly and placed in a muffle furnace. They were pre-calcined at 500℃ for 5 hours and then calcined at 930℃ for 10 hours to obtain a lithium-rich manganese-based cathode material with bulk molybdenum doping and surface lithium molybdate coating.

[0058] (2) Mix 5g of the bulk molybdenum-doped and surface lithium molybdate-coated lithium-rich manganese-based cathode material obtained in step (1) with 0.15g of ammonium oxalate and calcine at 400℃ for 2h under an argon atmosphere to obtain the modified lithium-rich manganese-based cathode material.

[0059] Example 2

[0060] This embodiment provides a modified lithium-rich manganese-based cathode material, including a lithium-rich manganese-based cathode material, wherein the bulk phase of the lithium-rich manganese-based cathode material has tungsten doping, and the surface phase of the lithium-rich manganese-based cathode material has a lithium tungstate coating layer and constructed oxygen vacancies.

[0061] This embodiment prepares the above-mentioned modified lithium-rich manganese-based cathode material using a method for synergistic modification of lithium-rich manganese-based cathode material with tungsten oxide and ammonium citrate. The steps are as follows:

[0062] (1) Weigh Ni according to the following ratio: tungsten accounts for 1% of the total molar amount of transition metal elements in the raw material and lithium is in a molar ratio of 1.45 to the total transition metal elements. 0.35 Co 0.05 Mn 0.6 (OH)2, tungsten oxide and lithium carbonate were mixed evenly and placed in a muffle furnace. They were pre-calcined at 600℃ for 4 hours and then calcined at 1000℃ for 12 hours to obtain a lithium-rich manganese-based cathode material with bulk tungsten doping and surface lithium tungstate coating.

[0063] (2) Mix 5g of the bulk tungsten-doped and surface lithium tungstate-coated lithium-rich manganese-based cathode material obtained in step (1) with 0.10g of ammonium citrate and calcine at 400°C for 2h under a nitrogen atmosphere to obtain the modified lithium-rich manganese-based cathode material.

[0064] Example 3

[0065] This embodiment provides a modified lithium-rich manganese-based cathode material, including a lithium-rich manganese-based cathode material, wherein the bulk phase of the lithium-rich manganese-based cathode material is doped with tantalum, and the surface phase of the lithium-rich manganese-based cathode material has a lithium tantalate coating layer and constructed oxygen vacancies.

[0066] This embodiment describes the preparation of the modified lithium-rich manganese-based cathode material using a method that synergistically modifies lithium-rich manganese-based cathode material with tantalum oxide and ammonium oxalate. The steps are as follows:

[0067] (1) Weigh Ni according to the following ratio: tantalum accounts for 2% of the total molar amount of transition metal elements in the raw material and lithium is in a molar ratio of 1.45 to the total transition metal elements. 0.4 Co 0.05 Mn 0.55 CO3, tantalum oxide and lithium carbonate were mixed evenly and placed in a muffle furnace. They were pre-calcined at 350°C for 6 hours and then calcined at 750°C for 15 hours to obtain a lithium-rich manganese-based cathode material with bulk tantalum doping and surface lithium tantalate coating.

[0068] (2) Mix 5g of the bulk tantalum-doped and surface lithium tantalate-coated lithium-rich manganese-based cathode material obtained in step (1) with 0.025g of ammonium oxalate and calcine at 300°C for 2h under an argon atmosphere to obtain the modified lithium-rich manganese-based cathode material.

[0069] Example 4

[0070] This embodiment provides a modified lithium-rich manganese-based cathode material, including a lithium-rich manganese-based cathode material, wherein the bulk phase of the lithium-rich manganese-based cathode material is doped with tantalum, and the surface phase of the lithium-rich manganese-based cathode material has a lithium tantalate coating layer and constructed oxygen vacancies.

[0071] This embodiment describes the preparation of the modified lithium-rich manganese-based cathode material using a method that combines tantalum oxide and ammonium carbonate for synergistic modification. The steps are as follows:

[0072] (1) Weigh Ni according to the following ratio: tantalum accounts for 0.2% of the total molar amount of transition metal elements in the raw material and lithium is in a molar ratio of 1.45 to the total transition metal elements. 0.31 Co 0.07 Mn 0.62 CO3, tantalum oxide and lithium carbonate were mixed evenly and placed in a muffle furnace. They were pre-calcined at 500°C for 5 hours and then calcined at 930°C for 10 hours to obtain a lithium-rich manganese-based cathode material with bulk tantalum doping and surface lithium tantalate coating.

[0073] (2) Mix 5g of the bulk tantalum-doped, surface lithium tantalate-coated lithium-rich manganese-based cathode material obtained in step (1) with 0.20g of ammonium carbonate and calcine at 500°C for 1h in a compressed air atmosphere to obtain the modified lithium-rich manganese-based cathode material.

[0074] Example 5

[0075] This embodiment provides a modified lithium-rich manganese-based cathode material, including a lithium-rich manganese-based cathode material, wherein the bulk phase of the lithium-rich manganese-based cathode material has niobium doping, and the surface phase of the lithium-rich manganese-based cathode material has a lithium niobate coating layer and constructed oxygen vacancies.

[0076] This embodiment describes the preparation of the modified lithium-rich manganese-based cathode material using a method that synergistically modifies lithium-rich manganese-based cathode material with niobium oxide and ammonium bicarbonate. The steps are as follows:

[0077] (1) Weigh Ni according to the following ratio: 4% of niobium in the total molar amount of transition metal elements in the raw material and 1.45 molar ratio of lithium to total transition metal elements. 0.35 Co 0.05 Mn 0.6 CO3, niobium oxide and lithium carbonate were mixed evenly and placed in a muffle furnace. They were pre-calcined at 500°C for 5 hours and then calcined at 930°C for 10 hours to obtain a lithium-rich manganese-based cathode material with bulk niobium doping and surface lithium niobate coating.

[0078] (2) Mix 5g of the bulk niobium-doped and surface lithium niobate-coated lithium-rich manganese-based cathode material obtained in step (1) with 0.25g of ammonium bicarbonate and calcine at 200°C for 4h under a nitrogen atmosphere to obtain the modified lithium-rich manganese-based cathode material.

[0079] Example 6

[0080] This embodiment provides a method for preparing a modified lithium-rich manganese-based cathode material. The only difference between this method and Example 1 is that the amount of ammonium oxalate in step (2) of the preparation method is adjusted to 0.05g, while the rest is the same as in Example 1.

[0081] Example 7

[0082] This embodiment provides a method for preparing a modified lithium-rich manganese-based cathode material. The only difference between this method and Example 1 is that the amount of ammonium oxalate in step (2) of the preparation method is adjusted to 0.25g, while the rest is the same as in Example 1.

[0083] Example 8

[0084] This embodiment provides a method for preparing a modified lithium-rich manganese-based cathode material. The only difference between this method and Example 1 is that the amount of ammonium oxalate in step (2) of the preparation method is adjusted to 0.01g, while the rest is the same as in Example 1.

[0085] Example 9

[0086] This embodiment provides a method for preparing a modified lithium-rich manganese-based cathode material. The only difference between this method and Example 1 is that the amount of ammonium oxalate in step (2) of the preparation method is adjusted to 0.3g, while the rest is the same as in Example 1.

[0087] Example 10

[0088] This embodiment provides a method for preparing modified lithium-rich manganese-based cathode materials. The difference between this method and that of Example 1 is that the proportion of molybdenum in the total molar amount of transition metal elements in the raw materials in step (1) is replaced with 0.05%, while the rest is the same as in Example 1.

[0089] Example 11

[0090] This embodiment provides a method for preparing modified lithium-rich manganese-based cathode materials. The difference between this method and that of Example 1 is that the proportion of molybdenum in the total molar amount of transition metal elements in the raw materials in step (1) is replaced with 5%, while the rest is the same as in Example 1.

[0091] Example 12

[0092] This embodiment provides a method for preparing a modified lithium-rich manganese-based cathode material. The only difference between this method and Example 1 is that the calcination temperature in step (2) of the preparation method is changed to 100°C, while the rest is the same as in Example 1.

[0093] Example 13

[0094] This embodiment provides a method for preparing a modified lithium-rich manganese-based cathode material. The only difference between this method and Example 1 is that the calcination temperature in step (2) of the preparation method is changed to 600°C, while the rest is the same as in Example 1.

[0095] Comparative Example 1

[0096] This comparative example provides a lithium-rich manganese-based cathode material, which differs from Example 1 only in that: the bulk phase of the lithium-rich manganese-based cathode material does not contain any transition metal doping, and its surface phase does not contain a lithium molybdate coating layer or oxygen vacancies.

[0097] This comparative example provides a method for preparing the above-mentioned lithium-rich manganese-based cathode material, the steps of which are as follows:

[0098] Lithium carbonate and lithium-rich manganese precursor were weighed according to a molar ratio of lithium element in lithium carbonate to transition metal element in lithium-rich manganese-based cathode material of 1.45, mixed evenly, and then placed in a muffle furnace for pre-calcination at 500℃ for 5 hours, followed by calcination at 930℃ for 10 hours to obtain lithium-rich manganese-based cathode material.

[0099] Comparative Example 2

[0100] This comparative example provides a modified lithium-rich manganese-based cathode material, which differs from Example 1 in that the modified lithium-rich manganese-based cathode material only includes bulk molybdenum doping and a surface lithium molybdate coating layer, and does not contain oxygen vacancies constructed in the surface phase. Accordingly, this comparative example provides a method for preparing the above-mentioned modified lithium-rich manganese-based cathode material, which is the same as step (1) in Example 1. All other steps are the same as in Example 1.

[0101] Comparative Example 3

[0102] This comparative example provides a modified lithium-rich manganese-based cathode material, which differs from Example 1 in that it does not contain oxygen vacancies constructed in the surface phase.

[0103] Meanwhile, this comparative example provides a method for preparing the above-mentioned modified lithium-rich manganese-based cathode material. The difference between this method and Example 1 is that in step (1), the proportion of molybdenum in the total molar amount of transition metal elements in the raw material is replaced with 0.2%, and the preparation process in step (2) is omitted. All other steps are the same as in Example 1.

[0104] Comparative Example 4

[0105] This comparative example provides a modified lithium-rich manganese-based cathode material, which differs from Example 1 in that it does not contain oxygen vacancies constructed in the surface phase.

[0106] Meanwhile, this comparative example provides a method for preparing the above-mentioned modified lithium-rich manganese-based cathode material. The difference between this method and Example 1 is that in step (1), the proportion of molybdenum in the total molar amount of transition metal elements in the raw material is 1%, and the preparation process in step (2) is omitted. The rest is the same as in Example 1.

[0107] Comparative Example 5

[0108] This comparative example provides a modified lithium-rich manganese-based cathode material, which differs from Example 1 in that the modified lithium-rich manganese-based cathode material includes a lithium-rich manganese-based cathode material and oxygen vacancies constructed on the surface.

[0109] This comparative example provides a method for preparing a lithium-rich manganese-based cathode material modified with ammonium oxalate, the steps of which are as follows:

[0110] (1) Weigh and mix lithium carbonate with lithium rich manganese-based precursor at a ratio of lithium element to transition metal element of 1.45 and mix them evenly. Then place them in a muffle furnace and pre-calcine at 500℃ for 5h, and then calcine at 930℃ for 10h to obtain lithium rich manganese-based cathode material.

[0111] (2) Mix 5g of lithium-rich manganese-based cathode material obtained in step (1) with 0.15g of ammonium oxalate and calcine at 400℃ for 2h under argon atmosphere to obtain modified lithium-rich manganese-based cathode material.

[0112] Assemble the button battery and conduct performance tests:

[0113] (1) The assembly process of a button battery is as follows:

[0114] The positive electrode material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) provided in the above embodiments and comparative examples were weighed at a mass ratio of 8:1:1 and dissolved in N-methylpyrrolidone (NMP) and mixed thoroughly. Then, the slurry was coated onto aluminum foil using a coater and dried in a vacuum drying oven at 80°C for 8 hours. Finally, the aluminum foil was stamped into 1.13 cm thick sheets. 2 The positive electrode is obtained by forming a circle.

[0115] The obtained positive electrode sheet was used as the positive electrode, the lithium metal sheet as the counter electrode, and the porous polypropylene membrane (Celgard 2400, USA) was used as the separator to separate the positive and counter electrodes. The CR 2032 button cell was assembled in an argon glove box.

[0116] (2) Performance Testing: A battery testing system (Landian CT2001A, Wuhan, China) was used, where 1C = 250mAh / g. Rate testing was conducted at 0.1C, 0.2C, 0.5C, and 1.0C rates within a voltage range of 2.0–4.55V. Cycling performance testing was performed at 0.1C rate under conditions of 2.0–4.55V. The test results are shown in Table 1.

[0117] Table 1

[0118] The test results show that:

[0119] (1) As can be seen from Examples 1-7, this application synergistically modifies lithium-rich manganese-based cathode materials with a high-valence transition metal source and acid amine compounds. Simultaneously, it incorporates doping with high-valence transition metal elements, a lithium metal coating layer, and the construction of surface oxygen vacancies. The combined effect of these three factors enables the battery to achieve a discharge specific capacity of up to 256.7 mAh g at 0.1C. -1 Above, the discharge specific capacity at 0.2C can reach 250.1 mAh g. -1 Above, the discharge specific capacity at 0.5C can reach 241.3 mAh g. -1 Above, the discharge specific capacity at 1C can reach 231.2 mAh g. -1 The above demonstrates a technical effect where the capacity retention rate can reach over 91.0% after 100 cycles at 0.1C.

[0120] (2) By comparing Example 1 with Examples 8-9, it can be seen that the amount of acid amine compound added in the preparation method provided in this application will affect the performance of the modified lithium-rich manganese-based cathode material. If the amount of acid amine compound added is too low, the amount of reducing gas generated is too small, which is insufficient to enhance the structural stability by affecting the local Mn coordination environment and cannot effectively alleviate the problem of irreversible oxygen release. If the amount of acid amine compound added is too high, the amount of reducing gas generated is too large, which may induce the migration of transition metal ions, resulting in the phase transition of spinel and rock salt phases, which may have an adverse effect on electrochemical performance.

[0121] (3) A comparison between Example 1 and Examples 10-11 shows that, in this application, controlling the amount of high-valence transition metal elements can maximize the electrochemical performance of lithium-rich manganese cathode materials. If the amount of high-valence transition metal elements added is too small, the amount of high-valence metal elements is insufficient to expand the lithium interlayer spacing, thus failing to effectively promote the rapid migration of lithium ions; if the amount of high-valence transition metal elements added is too large, the high-valence transition metals may form an excessively thick and unevenly distributed lithium oxide coating layer on the material surface, thereby leading to a decrease in electrochemical performance.

[0122] (4) By comparing Example 1 with Examples 12-13, it can be seen that adjusting the calcination temperature after mixing the lithium-rich manganese-based cathode material core with acid amine compounds can effectively achieve the construction of oxygen vacancies; if the calcination temperature is too low, the acid amine compounds cannot be completely decomposed; if the calcination temperature is too high, it may affect the original structure of the cathode material.

[0123] (5) By comparing Example 1 and Comparative Example 1, it can be seen that the present application can obtain high-performance lithium-rich manganese-based cathode materials by synergistic modification of lithium-rich manganese-based cathode materials with high-valence transition metal sources and acid amine compounds. However, when high-valence transition metal oxides and acid amine compounds are not used for synergistic modification, the unmodified lithium-rich manganese-based cathode materials are applied to batteries, and the rate performance and cycle performance of the batteries are poor.

[0124] (6) By comparing Example 1 with Comparative Examples 2-4, it can be seen that if the modification of acid amine compounds is not used in this application, only high-valence transition metal oxides are used for modification to obtain lithium-rich manganese-based cathode materials with lithium molybdate coating on the surface and molybdenum doping in the bulk phase. This cannot effectively alleviate a series of problems caused by irreversible release of oxygen on the material surface, and thus it is difficult to effectively improve the cycle performance and rate performance of the battery.

[0125] (7) By comparing Example 1 and Comparative Example 5, it can be seen that if high-valence transition metal oxidation is not used for modification in this application, the construction of oxygen vacancies on the surface of lithium-rich manganese-based cathode material alone cannot effectively alleviate the corrosion of the material by the electrolyte, nor can it effectively improve the structural stability of the material, thus the electrochemical performance of the battery cannot be significantly improved.

[0126] In summary, this application achieves the simultaneous doping of high-valence transition metal elements, coating of metal lithides, and construction of oxygen vacancies in lithium-rich manganese-based cathode materials by introducing high-valence transition metal sources and synergistic modification of acid amine compounds, thereby significantly improving the electrochemical performance of lithium-rich manganese cathode materials.

[0127] The applicant declares that the above description is only a specific implementation of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A modified lithium-rich manganese-based positive electrode material, comprising a lithium-rich manganese-based positive electrode material, wherein a high-valence transition metal element is doped in a bulk phase of the lithium-rich manganese-based positive electrode material, and a surface phase of the lithium-rich manganese-based positive electrode material has a metal lithium compound coating layer and oxygen vacancies.

2. The modified lithium-rich manganese-based positive electrode material of claim 1, wherein, The high-valence transition metal element comprises any one or a combination of at least two of niobium, molybdenum, tungsten or tantalum.

3. The modified lithium-rich manganese-based positive electrode material according to claim 1 or 2, wherein The metal lithium compound in the metal lithium compound coating layer comprises any one or a combination of at least two of lithium niobate, lithium molybdate, lithium tungstate or lithium tantalate. 4.A method for preparing the modified lithium-rich manganese-based positive electrode material according to any one of claims 1 to 3, comprising the following steps: (1) mixing a lithium-rich manganese-based precursor, a lithium source and a high-valence transition metal source, and then performing a lithiation reaction to obtain a lithium-rich manganese-based positive electrode material with a bulk phase doped with a high-valence transition metal element and a surface phase coated with a metal lithium compound; (2) mixing the lithium-rich manganese-based positive electrode material with a bulk phase doped with a high-valence transition metal element and a surface phase coated with a metal lithium compound obtained in step (1) with an ammonium acid compound, and then performing calcination to obtain the modified lithium-rich manganese-based positive electrode material.

5. The production method according to claim 4, wherein The lithium-rich manganese-based precursor includes Ni x Co y Mn 1-x-y (OH)2or Ni x Co y Mn 1-x-y CO3, wherein 0.3 < x < 0.4, and y < 0.

1. Optionally, the lithium source comprises lithium carbonate and / or lithium hydroxide. Optionally, the high-valence transition metal source comprises a high-valence transition metal oxide. Optionally, the high-valence transition metal oxide comprises any one or a combination of at least two of niobium oxide, molybdenum oxide, tungsten oxide or tantalum oxide.

6. The production method according to claim 4 or 5, wherein, In step (1), the ratio of the total molar amount of transition metal elements in the lithium-rich manganese-based precursor and transition metal elements in the high-valence transition metal source to the molar amount of lithium elements in the lithium source is 1:(1.3-1.6). Optionally, the molar percentage of the high-valence transition metal element is 0.1-4% based on the total molar amount of transition metal elements in the lithium-rich manganese-based precursor and transition metal elements in the high-valence transition metal source in step (1).

7. The method of making according to any one of claims 4-6, wherein, The temperature of the lithiation reaction in step (1) is 750-1000℃. Optionally, the time of the lithiation reaction in step (1) is 10-15h.

8. The method of making according to any one of claims 4-7, wherein, The mixture obtained after mixing in step (1) is further pre-fired before the lithiation reaction. Optionally, the temperature of the pre-firing is 350-600℃. Optionally, the time of the pre-firing is 4-6h.

9. The method of making according to any one of claims 4-8, wherein, The ammonium acid compound in step (2) comprises any one or a combination of at least two of ammonium carbonate, ammonium bicarbonate, ammonium oxalate, ammonium citrate or ammonium tartrate. Optionally, the amount of the ammonium acid compound added in step (2) is 0.5-5% based on 100% of the mass of the lithium-rich manganese-based positive electrode material with a bulk phase doped with a high-valence transition metal element and a surface phase coated with a metal lithium compound obtained in step (1).

10. The method of making according to any one of claims 4-9, wherein, The temperature of the calcination in step (2) is 200-500℃. Optionally, the time of the calcination in step (2) is 1-4h. Optionally, the gas in the atmosphere of the calcination in step (2) comprises at least one of compressed air, nitrogen or an inert gas. 11.A positive electrode comprising the modified lithium-rich manganese-based positive electrode material according to any one of claims 1 to 3. 12.A lithium ion battery comprising the positive electrode according to claim 11.

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