Surface-modified spinel lithium manganate cathode material and preparation method thereof, lithium battery

Abstract

The application provides a surface-modified spinel lithium manganate positive electrode material and a preparation method and a lithium battery thereof, and the lithium battery is prepared by a solid-phase co-sintering method and a subsequent hydrothermal treatment method, and a core-shell structure with same composition elements but different element contents and valence states of the surface and the interior is obtained, wherein the inner core is spinel lithium manganate close to a stoichiometric ratio, and the surface is an amorphous lithium-manganese-oxygen layer with high lithium content and high manganese valence directly obtained through in-situ conversion; the lithium battery has better chemical bonding and mechanical stability, can effectively hinder the corrosion of electrolyte on the lithium manganate and inhibit the dissolution of Mn elements in the lithium manganate, and can remain stable in a long cycle process.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically to a surface-modified spinel-type lithium manganese oxide cathode material, its preparation method, and a lithium battery. Background Technology

[0002] Lithium-ion batteries possess advantages such as high operating voltage, high energy density, low self-discharge rate, and good cycle life, and have been widely used in electronic products such as mobile phones, laptops, and cameras. They also show great promise for emerging fields such as electric vehicles and energy storage power stations. Compared to 3C electronic products, electric vehicles and energy storage power stations place higher demands on the lifespan, safety, and cost of lithium-ion batteries.

[0003] Among all current cathode materials, spinel-type lithium manganese oxide (LiMn2O4) has advantages such as abundant manganese resources, low cost, high safety, and fast charge / discharge capabilities, making it very suitable for applications requiring large amounts of electrical energy storage units, such as electric vehicles and energy storage. However, lithium manganese oxide cathode materials suffer from poor cycle life and poor high-temperature stability due to the easy dissolution of Mn in the electrolyte and the Jahn-Teller effect, which limits their further large-scale application.

[0004] At present, the main approach is to modify lithium manganese oxide materials to address their poor cycle life and high-temperature performance. The main methods include morphology control, heteroelement doping, and coating.

[0005] Morphology control involves controlling the proportion of exposed crystal faces and reducing the contact area between particles and electrolyte by controlling the microstructure of lithium manganese oxide. This reduces the dissolution of Mn in the electrolyte and the occurrence of other side reactions. However, it does not completely solve the problem of Mn dissolution, and the rate capability of lithium manganese oxide is also affected by the reduced contact area between the material and the electrolyte.

[0006] Heterogeneous element doping involves adding metallic or non-metallic elements (such as Ti, Mg, Al, Cr, Co, Ni, Fe, P, F, etc.) during the synthesis of lithium manganese oxide to reduce lattice distortion during cycling, suppress the Jahn-Teller effect, and improve cycling performance. However, the problem of Mn element dissolution in electrolyte has not been solved.

[0007] Coating involves coating the surface of lithium manganese oxide particles with a layer of metal oxide, fluorine compound, phosphate compound, etc., to prevent direct contact between the material and the electrolyte, thereby reducing the dissolution of manganese (Mn) in the electrolyte and improving the battery's cycle performance and high-temperature stability. However, traditional surface coating methods typically involve solid-state sintering or solution reaction followed by sintering. The resulting coating layer is difficult to form a continuous and uniform coating, making it difficult to completely prevent direct contact between the cathode material and the electrolyte. While the ALD (Alternating Layer Deposition) technology developed in recent years can achieve uniform coating on the surface of lithium manganese oxide, it suffers from high cost and difficulties in large-scale production. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by providing a surface-modified spinel-type lithium manganese oxide cathode material and its preparation method. Through solid-state co-sintering and subsequent hydrothermal treatment, a core-shell structure with the same constituent elements but different elemental contents and valence states on the surface and inside is prepared. The core is spinel lithium manganese oxide in close stoichiometric proportions, and the surface is an amorphous lithium-manganese-oxygen layer with high lithium content and high manganese valence state obtained by direct in-situ conversion. While effectively preventing electrolyte erosion of lithium manganese oxide and inhibiting the dissolution of Mn element in lithium manganese oxide, it also has better chemical bonding and mechanical stability, and can remain stable during long-term cycling.

[0009] According to a first aspect of the present invention, a method for preparing a surface-modified spinel-type lithium manganese oxide cathode material is provided, comprising the following steps:

[0010] The first precursor is obtained by uniformly mixing the manganese source compound and the first lithium source compound. The first precursor is then placed in a muffle furnace for solid-state sintering to obtain spinel-type lithium manganese oxide.

[0011] Spinel-type lithium manganese oxide is mixed with an oxidant and a second lithium source compound in an aqueous solution to obtain a mixture. The mixture is then subjected to hydrothermal treatment to directly and in situ convert the surface of the spinel-type lithium manganese oxide into an amorphous lithium-manganese-oxygen layer. After the reaction is completed, the mixture is filtered or centrifuged, washed, and dried to obtain a surface-modified spinel-type lithium manganese oxide cathode material.

[0012] Among them, the Li:Mn molar ratio in the amorphous lithium-manganese-oxygen layer is 1.07 to 1.23 higher than that in spinel-type lithium manganese oxide, and the average valence state of manganese in the amorphous lithium-manganese-oxygen layer is 0.17 to 0.6 higher than that in spinel-type lithium manganese oxide.

[0013] Preferably, in the first precursor, the molar ratio of Li:Mn is 0.4 to 0.6.

[0014] Preferably, the manganese source compound is one or more of manganese dioxide, manganese trioxide, manganese tetroxide, manganese monoxide, manganese carbonate, manganese oxalate, manganese acetate, and manganese nitrate.

[0015] Preferably, the first lithium source compound is one or more of lithium hydroxide, lithium carbonate, lithium oxalate, lithium nitrate, lithium chloride, lithium fluoride, and lithium acetate.

[0016] Preferably, in the mixture, the molar ratio of Li in the second lithium source compound to Mn in spinel-type lithium manganese oxide is 0.5 to 100, and the molar ratio of the oxidant to the spinel-type lithium manganese oxide matrix is ​​0.1 to 100.

[0017] Preferably, the second lithium source compound is one or more of lithium hydroxide, lithium carbonate, lithium oxalate, lithium nitrate, lithium chloride, lithium fluoride, and lithium acetate.

[0018] Preferably, the oxidant is one or more of hydrogen peroxide, ammonium thiosulfate, sodium thiosulfate, potassium thiosulfate, ammonium persulfate, sodium persulfate, potassium persulfate, peracetic acid, sodium percarbonate, sodium perborate, and potassium perborate.

[0019] Preferably, the solid-state sintering conditions are as follows:

[0020] The sintering temperature is 600–1000℃, the heating rate is 1–15℃ / min, the holding time is 2–24h, and the cooling rate after sintering is 1–15℃ / min.

[0021] Preferably, the conditions for the hydrothermal treatment are as follows:

[0022] The hydrothermal treatment temperature is 100–250℃, and the holding time is 0.5–24h.

[0023] According to a second aspect of the present invention, a surface-modified spinel-type lithium manganese oxide cathode material is also provided, which is prepared by the aforementioned method for preparing surface-modified spinel-type lithium manganese oxide cathode materials.

[0024] Preferably, the cathode material has a spinel-type lithium manganese oxide core, and the surface of the spinel-type lithium manganese oxide has an amorphous lithium-manganese-oxygen layer that is directly converted in situ, forming a core-shell structure with spinel-type lithium manganese oxide core and amorphous lithium-manganese-oxygen layer as outer shell;

[0025] Among them, the Li:Mn molar ratio in the amorphous lithium-manganese-oxygen layer is 1.07 to 1.23 higher than that in spinel-type lithium manganese oxide, and the average valence state of manganese in the amorphous lithium-manganese-oxygen layer is 0.17 to 0.6 higher than that in spinel-type lithium manganese oxide.

[0026] Preferably, the Li:Mn molar ratio in the amorphous lithium-manganese-oxygen layer is 1.7 to 2, and the average valence state of manganese is +3.7 to +4.

[0027] The Li:Mn molar ratio in spinel-type lithium manganese oxide is 0.47 to 0.53, and the average valence state of manganese is +3.4 to +3.53.

[0028] Preferably, the thickness of the amorphous lithium-manganese-oxygen layer is 2 to 15 nm.

[0029] According to a third aspect of the present invention, a lithium battery is also provided, wherein the positive electrode of the lithium battery is prepared by the aforementioned method for preparing surface-modified spinel-type lithium manganese oxide positive electrode material.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. The preparation method of the surface-modified spinel-type lithium manganese oxide cathode material of the present invention firstly obtains spinel-type lithium manganese oxide by solid-state sintering, and then directly transforms the surface of lithium manganese oxide into a uniform amorphous lithium-manganese-oxygen layer with high lithium content and high manganese valence state under hydrothermal treatment in solution conditions, thus preparing a core-shell structure with the same constituent elements but different element content and valence state on the surface and inside, wherein the core is spinel lithium manganese oxide with a near stoichiometric ratio, and the surface is an amorphous lithium-manganese-oxygen layer with high lithium content and high manganese valence state.

[0032] The cathode material obtained by the method of the present invention can effectively suppress the dissolution of Mn and the side reactions of the electrolyte on the surface of lithium manganese oxide, thereby improving the cycle performance of the material. In addition, the surface layer is directly converted from lithium manganese oxide and has good chemical bonding and mechanical contact with the core lithium manganese oxide, which can maintain stability and provide continuous protection during long-term electrode cycling.

[0033] 2. The surface-modified spinel-type lithium manganese oxide cathode material of the present invention can remain stable during long-term charge and discharge processes. After 1400 cycles at 1C rate, it can still retain more than 80% of the initial capacity and has excellent cycle life.

[0034] 3. Compared with methods of doping lithium manganese oxide with heterogeneous elements or coating the surface of lithium manganese oxide with other materials, the method of the present invention can uniformly transform the surface of lithium manganese oxide into a highly stable layer under solution conditions. The material preparation process is simple, has a good compatibility with existing lithium manganese oxide production processes, is low in cost, and is easy to industrialize. Therefore, it has significant practical significance for industrial application. Attached Figure Description

[0035] Figure 1 This is a process flow diagram of the preparation method of the surface-modified spinel-type lithium manganese oxide cathode material of the present invention.

[0036] Figure 2 This is the XRD pattern of the surface-modified lithium manganese oxide cathode material obtained in Example 1 of the present invention.

[0037] Figure 3 This is a SEM image of the surface-modified lithium manganese oxide cathode material obtained in Example 1 of this invention.

[0038] Figure 4 a and 4b are TEM images of the surface-modified lithium manganese oxide cathode material obtained in Example 1 of this invention at different magnifications.

[0039] Figure 5 This is the XRD pattern of the lithium manganese oxide cathode material obtained in Comparative Example 1 of this invention.

[0040] Figure 6 This is a SEM image of the lithium manganese oxide cathode material obtained in Comparative Example 1 of this invention.

[0041] Figure 7 a and 7b are TEM images of the lithium manganese oxide cathode material obtained in Comparative Example 1 of this invention at different magnifications.

[0042] Figure 8 a is the XPS image of the surface-modified lithium manganese oxide cathode material obtained in Example 1 of this invention.

[0043] Figure 8 b is the XPS image of the surface-modified lithium manganese oxide cathode material obtained in Example 1 of this invention via Mn 3s.

[0044] Figure 9 a is the XPS diagram of the lithium manganese oxide cathode material obtained in Comparative Example 1 of this invention.

[0045] Figure 9 b is the XPS diagram of the lithium manganese oxide cathode material obtained in Comparative Example 1 of this invention through Mn 3s.

[0046] Figure 10 This is a cycle performance diagram of the surface-modified lithium manganese oxide composite cathode material obtained in Example 1 of the present invention.

[0047] Figure 11 This is a cycle performance diagram of the lithium manganese oxide cathode material obtained in Comparative Example 1 of this invention. Detailed Implementation

[0048] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0049] Various aspects of the invention are described in this disclosure with reference to the accompanying drawings, in which numerous illustrative embodiments are shown. The embodiments of this disclosure are not necessarily intended to encompass all aspects of the invention. It should be understood that the various concepts and embodiments described above, as well as those described below in more detail, can be implemented in any of a number of ways.

[0050] This invention provides a method for preparing a surface-modified spinel-type lithium manganese oxide cathode material. Through solid-state co-sintering and subsequent hydrothermal treatment, a more uniform surface-modified layer than surface coating is achieved in a solution environment, resulting in a core-shell structure with the same constituent elements but different element content and valence states on the surface and inside.

[0051] Compared with existing technologies that coat the surface of lithium manganese oxide with heterogeneous materials, the present invention can firstly achieve a more uniform surface modification layer in a solution environment than surface coating; secondly, the modified layer obtained by the present invention is directly converted from the surface layer of lithium manganese oxide particles, which has better chemical bonding and mechanical stability compared with heterogeneous contact of other materials coating the surface of lithium manganese oxide, and can remain stable during long-term cycling.

[0052] Combination Figure 1 As shown, in a preferred embodiment of the present invention, a method for preparing a surface-modified spinel-type lithium manganese oxide cathode material is provided, comprising the following steps:

[0053] The first precursor is obtained by uniformly mixing the manganese source compound and the first lithium source compound. The first precursor is then placed in a muffle furnace for solid-state sintering to obtain spinel-type lithium manganese oxide.

[0054] Spinel-type lithium manganese oxide is mixed with an oxidant and a second lithium source compound in an aqueous solution to obtain a mixture. The mixture is then subjected to hydrothermal treatment to directly and in situ convert the surface of the spinel-type lithium manganese oxide into an amorphous lithium-manganese-oxygen layer. After the reaction is completed, the mixture is filtered or centrifuged, washed, and dried to obtain a surface-modified spinel-type lithium manganese oxide cathode material.

[0055] Among them, the Li:Mn molar ratio in the amorphous lithium-manganese-oxygen layer is 1.07 to 1.23 higher than that in spinel-type lithium manganese oxide, and the average valence state of manganese in the amorphous lithium-manganese-oxygen layer is 0.17 to 0.6 higher than that in spinel-type lithium manganese oxide.

[0056] In a preferred embodiment, the molar ratio of Li:Mn in the first precursor is 0.4 to 0.6.

[0057] In a preferred embodiment, the manganese source compound is one or more of manganese dioxide, manganese trioxide, manganese tetroxide, manganese monoxide, manganese carbonate, manganese oxalate, manganese acetate, and manganese nitrate.

[0058] In a more preferred embodiment, the manganese source compound is manganese dioxide, manganese tetroxide, or manganese carbonate.

[0059] In a preferred embodiment, the first lithium source compound is one or more of lithium hydroxide, lithium carbonate, lithium oxalate, lithium nitrate, lithium chloride, lithium fluoride, and lithium acetate.

[0060] In a more preferred embodiment, the first lithium source compound is lithium hydroxide or lithium carbonate.

[0061] In a preferred embodiment, the molar ratio of Li in the second lithium source compound to Mn in spinel-type lithium manganese oxide in the mixture is 0.5 to 100, and the molar ratio of oxidant to spinel-type lithium manganese oxide matrix is ​​0.1 to 100.

[0062] In a preferred embodiment, the second lithium source compound is one or more of lithium hydroxide, lithium carbonate, lithium oxalate, lithium nitrate, lithium chloride, lithium fluoride, and lithium acetate.

[0063] In a more preferred embodiment, the second lithium source compound is lithium hydroxide, lithium nitrate, or lithium chloride.

[0064] In a preferred embodiment, the oxidant is one or more mixtures selected from hydrogen peroxide, ammonium thiosulfate, sodium thiosulfate, potassium thiosulfate, ammonium persulfate, sodium persulfate, potassium persulfate, peracetic acid, sodium percarbonate, sodium perborate, and potassium perborate.

[0065] In a more preferred embodiment, the oxidant is hydrogen peroxide, ammonium thiosulfate, or sodium thiosulfate.

[0066] In a preferred embodiment, the solid-state sintering conditions are as follows:

[0067] The sintering temperature is 700–1000℃, the heating rate is 1–15℃ / min, the holding time is 2–24h, and the cooling rate after sintering is 1–15℃ / min.

[0068] In a more preferred embodiment, the sintering temperature is 700–900°C, the heating rate is 5–10°C / min, the holding time is 10–24 h, and the cooling rate after sintering is 2–15°C / min.

[0069] In a preferred embodiment, the conditions for the hydrothermal treatment are as follows:

[0070] The hydrothermal treatment temperature is 100–250℃, and the holding time is 0.5–24h.

[0071] In a more preferred embodiment, the hydrothermal treatment temperature is 150–200°C, and the holding time is 1–6 hours.

[0072] In a preferred embodiment, the drying temperature is 40–400°C, and the holding time is 0.5–24 h.

[0073] This invention provides, by way of example, a method for preparing a surface-modified spinel-type lithium manganese oxide cathode material, comprising:

[0074] (1) Weigh the manganese source compound and the first lithium source compound at a molar ratio of Li:Mn = 0.4 to 0.6. Put the weighed raw materials into a ball mill jar, add an equal mass of ethanol and agate balls with twice the mass of the raw materials, and ball mill at 250 rpm for 8 hours to obtain the lithium manganese oxide precursor.

[0075] The lithium manganese oxide precursor is placed in a muffle furnace and heated to 700-1000°C at a rate of 1-15°C / min and held at that temperature. Then it is cooled to room temperature at a rate of 1-15°C / min and removed to obtain spinel-type lithium manganese oxide.

[0076] (2) Add spinel-type lithium manganese oxide to an aqueous solution containing a second lithium source compound and an oxidant, wherein the molar ratio of Li in the second lithium source compound to Mn in the spinel-type lithium manganese oxide matrix is ​​0.5 to 100, and the molar ratio of the oxidant to the spinel-type lithium manganese oxide matrix is ​​0.1 to 100.

[0077] The above solution was placed in a polytetrafluoroethylene hydrothermal tank and sealed in a stainless steel reactor. The temperature was raised to 100-250°C and kept at that temperature. After cooling, the solution was filtered and washed with deionized water. Then, it was dried in a vacuum oven to obtain the surface-modified lithium manganese oxide cathode material.

[0078] In another exemplary embodiment, spinel-type lithium manganese oxide is added to an aqueous solution containing a second lithium source compound and an oxidant. The solution is then placed in a three-necked flask, a reflux condenser is added, and the solution is heated to 100–250°C in an oil bath and kept at that temperature. After cooling, the solution is filtered and washed with deionized water. Finally, it is dried in a vacuum oven to obtain a surface-modified lithium manganese oxide cathode material.

[0079] In another preferred embodiment of the present invention, a surface-modified spinel-type lithium manganese oxide cathode material is also provided, which is prepared by the aforementioned method for preparing surface-modified spinel-type lithium manganese oxide cathode material.

[0080] Preferably, the cathode material uses spinel-type lithium manganese oxide as the core, and the surface of the spinel-type lithium manganese oxide is transformed into an amorphous lithium-manganese-oxygen layer, forming a core-shell structure with spinel-type lithium manganese oxide as the core and the amorphous lithium-manganese-oxygen layer as the outer shell.

[0081] Among them, the Li:Mn molar ratio in the amorphous lithium-manganese-oxygen layer is 1.07 to 1.23 higher than that in spinel-type lithium manganese oxide, and the average valence state of manganese in the amorphous lithium-manganese-oxygen layer is 0.17 to 0.6 higher than that in spinel-type lithium manganese oxide.

[0082] Preferably, the Li:Mn molar ratio in the amorphous lithium-manganese-oxygen layer is 1.7 to 2, and the average valence state of manganese is +3.7 to +4.

[0083] The Li:Mn molar ratio in spinel-type lithium manganese oxide is 0.47 to 0.53, and the average valence state of manganese is +3.4 to +3.53.

[0084] Preferably, the thickness of the amorphous lithium-manganese-oxygen layer is 2 to 15 nm.

[0085] Preferably, the surface-modified spinel-type lithium manganese oxide cathode material consists of large particles composed of primary small particles of 50-100 nm, with a particle size range of 500-1000 nm.

[0086] In another preferred embodiment of the present invention, a lithium battery is also provided, wherein the positive electrode of the lithium battery is prepared by the aforementioned preparation method of surface-modified spinel-type lithium manganese oxide positive electrode material, and the lithium battery has excellent cycle stability.

[0087] The present invention will be further illustrated below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0088] Example 1

[0089] (1) Weigh the raw materials according to the molar ratio of LiOH∶MnCO3=1.05∶2, then put the raw materials into a ball mill jar, add an equal mass of ethanol and twice the mass of agate balls, and ball mill at 250 rpm for 8 h to obtain lithium manganese oxide precursor. Put the above precursor into a muffle furnace, heat it to 800℃ at a rate of 5℃ / min and hold it for 10 h, then cool it to room temperature at a rate of 2℃ / min and take it out to obtain lithium manganese oxide.

[0090] (2) Add 0.5g of lithium manganese oxide to 30mL of a solution containing 0.5M LiOH and 0.1M (NH4)2S2O8. Place the solution into a 50mL polytetrafluoroethylene hydrothermal tank and seal it in a stainless steel reactor. Heat the solution to 180℃ and keep it at that temperature for 3h. After cooling, filter the solution and wash it with deionized water. Then dry the solution in a vacuum oven at 80℃ to obtain the surface-modified lithium manganese oxide cathode material.

[0091] Example 2

[0092] (1) Weigh the raw materials according to the molar ratio of Li2CO3∶MnCO3=0.51∶1, then put the raw materials into a ball mill jar, add an equal mass of ethanol and twice the mass of agate balls, and ball mill at 250 rpm for 8 h to obtain lithium manganese oxide precursor. Put the above precursor into a muffle furnace, heat it to 800℃ at a rate of 5℃ / min and hold it for 10 h, then cool it to room temperature at a rate of 2℃ / min and take it out to obtain lithium manganese oxide.

[0093] (2) Add 0.5g of lithium manganese oxide to 30mL of a solution containing 1M LiOH and 0.2M H2O2. Place the solution into a 50mL polytetrafluoroethylene hydrothermal tank and seal it in a stainless steel reactor. Heat the solution to 150℃ and keep it at that temperature for 6h. After cooling, filter the solution and wash it with deionized water. Then dry the solution in a vacuum oven at 80℃ to obtain the surface-modified lithium manganese oxide cathode material.

[0094] Example 3

[0095] (1) Weigh the raw materials according to the molar ratio of LiOH∶MnO2=1.05∶2, then put the raw materials into a ball mill jar, add an equal mass of ethanol and twice the mass of agate balls, and ball mill at 250 rpm for 8 h to obtain lithium manganese oxide precursor. Put the above precursor into a muffle furnace, heat it to 800℃ at a rate of 5℃ / min and hold it for 10 h, then cool it to room temperature at a rate of 2℃ / min and take it out to obtain lithium manganese oxide.

[0096] (2) Add 5g of lithium manganese oxide to 100mL of a solution containing 1M LiCl and 0.2M (NH4)2S2O3. Place the solution into a 500mL three-necked flask, add a reflux condenser, heat to 150℃ in an oil bath and keep warm for 4h. After cooling, filter and wash with deionized water. Then dry in a vacuum oven at 80℃ to obtain surface-modified lithium manganese oxide cathode material.

[0097] Example 4

[0098] (1) Weigh the raw materials according to the molar ratio of LiOH∶MnCO3=1.03∶2, then put the raw materials into a ball mill jar, add an equal mass of ethanol and twice the mass of agate balls, and ball mill at 250 rpm for 8 h to obtain lithium manganese oxide precursor. Put the above precursor into a muffle furnace, heat it to 900℃ at a rate of 5℃ / min and hold it for 10 h, then cool it to room temperature at a rate of 2℃ / min and take it out to obtain lithium manganese oxide.

[0099] (2) Add 0.5g of lithium manganese oxide to 30mL of a solution containing 0.5M LiNO3 and 0.2M (NH4)2S2O8. Place the solution into a 50mL polytetrafluoroethylene hydrothermal tank and seal it in a stainless steel reactor. Heat the solution to 180℃ and keep it at that temperature for 3h. After cooling, filter the solution and wash it with deionized water. Then dry the solution in a vacuum oven at 180℃ to obtain the surface-modified lithium manganese oxide cathode material.

[0100] Example 5

[0101] (1) Weigh the raw materials according to the molar ratio of LiOH∶MnCO3=1.03∶2, then put the raw materials into a ball mill jar, add an equal mass of ethanol and twice the mass of agate balls, and ball mill at 250 rpm for 8 h to obtain lithium manganese oxide precursor. Put the above precursor into a muffle furnace, heat it to 900℃ at a rate of 5℃ / min and hold it for 10 h, then cool it to room temperature at a rate of 2℃ / min and take it out to obtain lithium manganese oxide.

[0102] (2) Add 0.5g of lithium manganese oxide to 30mL of a solution containing 1M LiNO3 and 0.2M Na2S2O8. Place the solution into a 50mL polytetrafluoroethylene hydrothermal tank and seal it in a stainless steel reactor. Heat the solution to 180℃ and keep it at that temperature for 3h. After cooling, filter the solution and wash it with deionized water. Then dry the solution in a vacuum oven at 180℃ to obtain the surface-modified lithium manganese oxide cathode material.

[0103] Example 6

[0104] (1) Weigh the raw materials according to the molar ratio of LiOH∶Mn3O4=1.05∶3, then put the raw materials into a ball mill jar, add an equal mass of ethanol and twice the mass of agate balls, and ball mill at 250 rpm for 8 h to obtain lithium manganese oxide precursor. Put the above precursor into a muffle furnace, heat it to 700℃ at a rate of 10℃ / min and hold it for 10 h, then cool it to room temperature at a rate of 2℃ / min and take it out to obtain lithium manganese oxide.

[0105] (2) Add 5g of lithium manganese oxide to 100mL of a solution containing 1M LiOH and 0.2M K2S2O3. Place the solution into a 500mL three-necked flask, add a reflux condenser, heat to 200℃ in an oil bath and keep warm for 1h. After cooling, filter and wash with deionized water. Then dry in a vacuum oven at 60℃ to obtain surface-modified lithium manganese oxide cathode material.

[0106] Example 7

[0107] (1) Weigh the raw materials according to the molar ratio of LiOH∶MnO2=1.05∶2, then put the raw materials into a ball mill jar, add an equal mass of ethanol and twice the mass of agate balls, and ball mill at 250 rpm for 8 h to obtain lithium manganese oxide precursor. Put the above precursor into a muffle furnace, heat it to 800℃ at a rate of 5℃ / min and hold it for 10 h, then cool it to room temperature at a rate of 2℃ / min and take it out to obtain lithium manganese oxide.

[0108] (2) Add 0.5g of lithium manganese oxide to 100mL of a solution containing 2M LiOH and 1M (NH4)2S2O3. Place the solution into a 500mL three-necked flask, add a reflux condenser, heat to 120℃ in an oil bath and keep warm for 0.5h. After cooling, filter and wash with deionized water. Then dry in a vacuum oven at 80℃ to obtain surface-modified lithium manganese oxide cathode material.

[0109] Example 8

[0110] (1) Weigh the raw materials according to the molar ratio of LiOH∶MnCO3=1.05∶1, then put the raw materials into a ball mill jar, add an equal mass of ethanol and twice the mass of agate balls, and ball mill at 250 rpm for 8 h to obtain lithium manganese oxide precursor. Put the above precursor into a muffle furnace, heat it to 800℃ at a rate of 5℃ / min and hold it for 10 h, then cool it to room temperature at a rate of 2℃ / min and take it out to obtain lithium manganese oxide.

[0111] (2) Add 0.5g of lithium manganese oxide to 200mL of a solution containing 2M LiOH and 1M (NH4)2S2O3. Place the solution into a 500mL three-necked flask, add a reflux condenser, heat to 120℃ in an oil bath and keep warm for 10min. After cooling, filter and wash with deionized water. Then dry in a vacuum oven at 80℃ to obtain the surface-modified lithium manganese oxide cathode material.

[0112] Comparative Example 1

[0113] Following the method in step (1) of Example 1, raw materials were weighed according to a molar ratio of LiOH:MnCO3 = 1.05:2. These raw materials were then placed in a ball mill jar, and an equal mass of ethanol and twice the mass of agate balls were added. After ball milling at 250 rpm for 8 hours, a lithium manganese oxide precursor was obtained. The precursor was then placed in a muffle furnace, heated to 800°C at a rate of 5°C / min, and held at that temperature for 10 hours. It was then cooled to room temperature at a rate of 2°C / min to obtain the lithium manganese oxide cathode material.

[0114] Comparative Example 2

[0115] According to step (1) of Example 2, the raw materials were weighed at a molar ratio of Li2CO3∶MnCO3=0.51∶1 and placed in a ball mill jar. An equal mass of ethanol was added. Agate balls were used for milling, with a mass ratio of agate balls to raw materials of 2∶1. The mixture was ball-milled at 250 rpm for 8 hours. After natural drying at room temperature, the agate balls were removed to obtain the lithium manganese oxide precursor. The precursor was placed in an air atmosphere reactor and heated to 800°C at a rate of 5°C / min and held for 10 hours. Then, it was cooled to room temperature at a rate of 2°C / min and removed to obtain spinel lithium manganese oxide material.

[0116] XRD, SEM, TEM

[0117] The surface-modified lithium manganese oxide cathode material obtained in Example 1 was subjected to XRD, SEM, and TEM tests, and the results are as follows:

[0118] Figure 2 The image shows the XRD pattern of the surface-modified lithium manganese oxide cathode material obtained in Example 1. As can be seen from the image, the sample has a spinel-structured lithium manganese oxide phase and no impurity phase is present.

[0119] Figure 3 This is a scanning electron microscope (SEM) image of the sample obtained in Example 1. As can be seen from the image, the sample is composed of large particles of uniform primary particles ranging from 50 to 100 nm in size, with the size of the large particles ranging from 500 to 1000 nm.

[0120] Figure 4 a and 4b are transmission electron microscope images of the sample obtained in Example 1 at different magnifications. It can be seen from the images that the surface layer of lithium manganese oxide particles does not have obvious lattice stripes and is in a disordered state. Therefore, a uniform and continuous amorphous lithium-manganese-oxygen layer is formed on the surface of lithium manganese oxide particles, and the thickness of the amorphous layer is about 3.5 nm.

[0121] The samples obtained in Comparative Example 1 were subjected to XRD, SEM, and TEM tests, and the results are as follows:

[0122] Figure 5 The image shows the XRD pattern of the sample in Comparative Example 1. As can be seen from the image, the prepared lithium manganese oxide has no other impurity phases and has high crystallinity.

[0123] Figure 6 The image shows the SEM image of the sample in Comparative Example 1. As can be seen from the image, its morphology is not significantly different from that of the sample in Example 1, and the particle size is similar.

[0124] Figure 7 a and 7b are TEM images of the sample from Comparative Example 1 at different magnifications. As can be seen from the images, the particle surface is smooth and there is no surface heterogeneous layer.

[0125] Therefore, through comparison and in conjunction with the above tests, it can be proven that the cathode material of the present invention has a core-shell structure, and the surface of the lithium manganese oxide particles has an amorphous lithium-manganese-oxygen layer.

[0126] XPS

[0127] XPS tests were performed on the surface-modified lithium manganese oxide cathode material obtained in Example 1, and the results are as follows:

[0128] Figure 8 This is the photoelectron spectrum (XPS) of the sample obtained in Example 1. Figure 8 As can be seen from a, the Li:Mn molar ratio on the surface is 0.64, while the Li:Mn molar ratio inside after etching is 0.51, indicating that the surface layer of the sample is a lithium-rich layer.

[0129] Local nanoscale EELS testing revealed that the Li:Mn molar ratio on the surface was 1.7–2. This is because the XPS testing depth is approximately 10 nm and is a comprehensive signal over a large scale range. The lithium:Mn ratio in the surface XPS may be biased. However, after etching to remove the influence of the surface layer, the lithium:Mn ratio in the internal XPS is accurate. Therefore, XPS testing can still confirm that the lithium:Mn molar ratio on the surface is significantly larger than that in the core, indicating that the surface layer of the sample is a lithium-rich layer.

[0130] Furthermore, the XPS plot of Mn 3s (8b) shows that the spacing between the Mn 3s peaks on the sample surface is smaller than that after etching, indicating that the Mn in the surface layer of the sample has a higher valence state than the interior, and is close to +4 valence.

[0131] The main reason for the dissolution of Mn in lithium manganese oxide is that the trace amounts of water remaining in the electrolyte react with fluorinated phosphate (LiPF6) to form HF, which readily undergoes a disproportionation reaction with Mn in LiMn2O4 to form Mn2O4. 4+ and Mn 2+ Mn 4+ MnO2 is easily formed and remains in the material, Mn 2+ It is easily soluble in the electrolyte. Therefore, the lithium-rich, high-valence manganese surface layer has high stability, which can effectively prevent the electrolyte from corroding the core lithium manganese oxide and inhibit the dissolution of low-valence manganese, thereby improving the cycle stability of the material.

[0132] XPS tests were performed on the samples obtained in Comparative Example 1, and the results are as follows:

[0133] Figure 9 a and 9b are XPS images of the sample in Comparative Example 1. As can be seen from the images, the molar ratio of Li:Mn is 0.52, and the valence state of Mn is close to +3.5.

[0134] Based on the aforementioned tests, it can be demonstrated that the present invention has successfully prepared a core-shell structure with the same constituent elements but different elemental contents and valence states on the surface and inside.

[0135] Electrochemical testing

[0136] The electrochemical testing method involved preparing a slurry by mixing the positive electrode material with a conductive agent (carbon black) and a binder (polyvinylidene fluoride PVDF) in a weight ratio of 80%:10%:10%. This slurry was then coated onto aluminum foil and dried in a vacuum oven to form an electrode sheet. A button cell was prepared using this electrode sheet as the working electrode, a lithium foil as the counter electrode, and 1M LiPF6 dissolved in ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1:1) as the electrolyte to test the electrochemical performance of the material. The test voltage range was 3.3–4.4 V, and the current density at 1C was 148 mA / g.

[0137] Figure 10 The image shows the cycle performance of the sample obtained in Example 1 after it was fabricated into an electrode sheet and tested at a current of 1C.

[0138] As shown in the figure, the electrode retains 81% of its initial capacity after 1400 cycles at a charge-discharge current of 1C at room temperature, indicating that the material has excellent cycle stability. This can be attributed to the fact that the uniform and continuous amorphous lithium-manganese-oxygen layer effectively inhibits the electrolyte's erosion of spinel lithium manganese oxide (the trace amounts of water remaining in the electrolyte react with fluorinated phosphate (LiPF6) to generate HF, which easily leads to the disproportionation reaction of Mn in LiMn2O4 to generate Mn). 4+ and Mn 2+ Mn 4+ MnO2 is easily formed and remains in the material, Mn 2+ It is easy to enter the electrolyte, and the lithium-rich, high-valence Mn in the amorphous layer can effectively eliminate the dissolution of low-valence Mn, thereby improving the cycle stability of the electrode.

[0139] The cycle performance of the cathode prepared in Comparative Example 1 is as follows: Figure 11 As shown, the positive electrode retains only 78.6% of its capacity after 300 cycles at a charge-discharge current of 1C at room temperature.

[0140] After the sample obtained in Example 2 was made into an electrode sheet, the cycling performance of the material was tested at a current of 1C, and it had 82% capacity retention after 1000 cycles.

[0141] After the sample obtained from Comparative Example 2 was made into an electrode sheet, the cycling performance of the material was tested at a charge-discharge current of 1C. It had a capacity retention of 78.1% after 300 cycles.

[0142] Comparing the electrochemical performance of the samples in Example 1 and Comparative Example 1, and the electrochemical performance of the samples in Example 2 and Comparative Example 2, it can be demonstrated that the cathode material of the present invention has superior cycle performance.

[0143] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for preparing a surface-modified spinel-type lithium manganese oxide cathode material, characterized in that, Includes the following steps: The first precursor is obtained by uniformly mixing the manganese source compound and the first lithium source compound. The first precursor is then placed in a muffle furnace for solid-state sintering to obtain spinel-type lithium manganese oxide. Spinel-type lithium manganese oxide is mixed with an oxidant and a second lithium source compound in an aqueous solution to obtain a mixture. The mixture is then subjected to hydrothermal treatment to directly and in situ convert the surface of the spinel-type lithium manganese oxide into an amorphous lithium-manganese-oxygen layer. After the reaction is completed, the mixture is filtered or centrifuged, washed, and dried to obtain a surface-modified spinel-type lithium manganese oxide cathode material. The hydrothermal treatment temperature is 100~250℃. Among them, the Li:Mn molar ratio in the amorphous lithium-manganese-oxygen layer is 1.07~1.23 higher than that in spinel-type lithium manganese oxide, and the average valence state of manganese in the amorphous lithium-manganese-oxygen layer is 0.17~0.6 higher than that in spinel-type lithium manganese oxide. The Li:Mn molar ratio in the amorphous lithium-manganese-oxygen layer is 1.7~2, and the average valence state of manganese is +3.7~+4; the thickness of the amorphous lithium-manganese-oxygen layer is 2~15nm.

2. The method for preparing the surface-modified spinel-type lithium manganese oxide cathode material according to claim 1, characterized in that, In the first precursor, the molar ratio of Li:Mn is 0.4~0.

6.

3. The method for preparing the surface-modified spinel-type lithium manganese oxide cathode material according to claim 1, characterized in that, The manganese source compound is one or more of manganese dioxide, manganese trioxide, manganese tetroxide, manganese monoxide, manganese carbonate, manganese oxalate, manganese acetate, and manganese nitrate.

4. The method for preparing the surface-modified spinel-type lithium manganese oxide cathode material according to claim 1, characterized in that, The first lithium source compound is one or a mixture of lithium hydroxide, lithium carbonate, lithium oxalate, lithium nitrate, lithium chloride, lithium fluoride, and lithium acetate.

5. The method for preparing the surface-modified spinel-type lithium manganese oxide cathode material according to claim 1, characterized in that, In the mixture, the molar ratio of Li in the second lithium source compound to Mn in spinel-type lithium manganese oxide is 0.5~100, and the molar ratio of oxidant to spinel-type lithium manganese oxide matrix is ​​0.1~100.

6. The method for preparing the surface-modified spinel-type lithium manganese oxide cathode material according to claim 1, characterized in that, The second lithium source compound is one or more of lithium hydroxide, lithium carbonate, lithium oxalate, lithium nitrate, lithium chloride, lithium fluoride, and lithium acetate.

7. The method for preparing the surface-modified spinel-type lithium manganese oxide cathode material according to claim 1, characterized in that, The oxidant is one or more of the following: hydrogen peroxide, ammonium thiosulfate, sodium thiosulfate, potassium thiosulfate, ammonium persulfate, sodium persulfate, potassium persulfate, peracetic acid, sodium percarbonate, sodium perborate, and potassium perborate.

8. The method for preparing the surface-modified spinel-type lithium manganese oxide cathode material according to any one of claims 1-7, characterized in that, The conditions for solid-state sintering are as follows: The sintering temperature is 600~1000℃, the heating rate is 1~15℃ / min, the holding time is 2~24 h, and the cooling rate after sintering is 1~15℃ / min.

9. The method for preparing the surface-modified spinel-type lithium manganese oxide cathode material according to any one of claims 1-7, characterized in that, The conditions for the hydrothermal treatment are as follows: The heat preservation time is 0.5~24 h.

10. A surface-modified spinel-type lithium manganese oxide cathode material, characterized in that, It is prepared by the preparation method of surface-modified spinel-type lithium manganese oxide cathode material according to any one of claims 1-9.

11. The surface-modified spinel-type lithium manganese oxide cathode material according to claim 10, characterized in that, The cathode material uses spinel-type lithium manganese oxide as its core, and the surface of the spinel-type lithium manganese oxide directly has an in-situ converted amorphous lithium-manganese-oxygen layer, forming a core-shell structure with spinel-type lithium manganese oxide as the core and the amorphous lithium-manganese-oxygen layer as the outer shell. Among them, the Li:Mn molar ratio in the amorphous lithium-manganese-oxygen layer is 1.07~1.23 higher than that in spinel-type lithium manganese oxide, and the average valence state of manganese in the amorphous lithium-manganese-oxygen layer is 0.17~0.6 higher than that in spinel-type lithium manganese oxide.

12. The surface-modified spinel-type lithium manganese oxide cathode material according to claim 11, characterized in that, The Li:Mn molar ratio in spinel-type lithium manganese oxide is 0.47~0.53, and the average valence state of manganese is +3.4~+3.

53.

13. A lithium battery, characterized in that, The positive electrode of the lithium battery is prepared by the preparation method of the surface-modified spinel-type lithium manganese oxide positive electrode material as described in any one of claims 1-9.

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