Single-crystal type lithium-rich manganese-based precursor, preparation method therefor and use thereof

Abstract

The present application relates to a single-crystal type lithium-rich manganese-based precursor, a preparation method therefor and a use thereof. According to the preparation method for the single-crystal type lithium-rich manganese-based precursor, oxalic acid is used to replace conventional ammonia water to serve as a complexing agent, and the characteristic that the complexing constant of oxalic acid and Mn2+ is high is utilized, so that metal ions in an obtained lithium-rich manganese-based precursor can be mixed at a molecular level, contact between particles is good, and the particle size is uniform. In addition, oxalic acid itself has reducibility, so that a reducing agent does not need to be additionally added in the preparation process; and once the lithium-rich manganese-based precursor is obtained, the lithium-rich manganese-based precursor is directly mixed with lithium carbonate in an air atmosphere, so that a single-crystal type lithium-rich manganese-based positive electrode material having excellent electrochemical performance and stable cycle performance can be obtained.

Description

A single crystal lithium-rich manganese-based precursor and its preparation method and application Technical Field

[0001] The present application belongs to the field of new energy battery technology, and relates to a precursor and a preparation method and application thereof, and in particular to a single-crystal lithium-rich manganese-based precursor and a preparation method and application thereof. Background Art

[0002] Lithium-rich manganese-based cathode materials (LRMs) have attracted widespread attention due to their advantages in specific energy density and cost, and are considered one of the most promising cathode materials for high-energy-density lithium-ion batteries. Currently, the most widely studied LRMs are mostly secondary spherical aggregates composed of primary particles. These materials suffer from structural instability, internal stress, poor robustness, and numerous voids. These materials are prone to structural collapse during charge and discharge, resulting in a large contact area with the electrolyte and increased side reactions, leading to decreased electrochemical performance, poor cycling performance, and poor thermal stability.

[0003] Therefore, it is necessary to prepare lithium-rich manganese-based positive electrode materials with a higher degree of single crystallinity.

[0004] CN108557905A discloses a lithium-rich manganese-based material precursor and a preparation method thereof, a lithium-rich manganese-based positive electrode material and a preparation method thereof, and a lithium battery. The lithium-rich manganese-based material precursor disclosed herein is a lithium-rich manganese-based material carbonate precursor with a flake-like morphology, a particle size of 1-7 μm, and a specific surface area of ​​8-50 m 2 / g. A "leaf-shaped" lithium-rich precursor is synthesized through carbonate co-precipitation, used as a sintering starting material, and fluxes H3BO3 and / or B2O3 are added during sintering. This process is complex, and the carbonate precursor has a low hardness, which easily forms small, irregular particles during ball milling, resulting in a decrease in the electrochemical performance of the resulting lithium-rich manganese-based cathode material.

[0005] Compared with carbonate precursors, hydroxide precursors have relatively higher particle density and tap density, and the particle size of the product is easier to control.

[0006] CN112158889A discloses a method for mass production of single crystal cobalt-free lithium-rich manganese-based binary material precursor, comprising the following steps: (1) nickel salt and manganese salt are prepared into solution A, NaOH solution is used as precipitant B, ammonia water is used as complexing agent C, and sodium sulfite solution is used as reducing agent D; (2) bottom liquid is prepared and N2 is introduced, the pH value of the bottom liquid is 11-13, the ammonia concentration is 3-10g / L, the temperature is controlled at 30-60℃, and the stirring speed is controlled between 200-500rpm; (3) solution A, solution B, solution C and solution D are added to the reactor at the same time, the pH is maintained at 10-12, the ammonia concentration of the supernatant is maintained at 3-10g / L, the temperature is maintained at 30-60℃, and the stirring speed is maintained at 200-500rpm; (4) after D50 reaches the target particle size, the feeding is stopped, and centrifugal washing, drying, screening, iron removal and packaging are performed. However, in this scheme, ammonia water is used as the complexing agent, and the Mn 2+ The complexing strength with ammonia water is low, and it is easily oxidized under alkaline conditions, which is not conducive to industrial production.

[0007] Therefore, it is necessary to provide a single-crystal lithium-rich manganese-based precursor with uniform mixing degree, high inter-particle contact and uniform particle size, as well as a preparation method and application thereof for lithium-rich manganese-based positive electrode materials, especially lithium-rich manganese-based positive electrode material precursors.

[0008] Summary of the Invention

[0009] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0010] The purpose of the present application is to provide a single-crystal lithium-rich manganese-based precursor and its preparation method and application. The preparation method can make the metal ions in the prepared lithium-rich manganese-based precursor reach a molecular-level mixing level, and the contact between particles is good and the particle size is uniform, and the preparation of single-crystal lithium-rich manganese-based positive electrode materials can be achieved under an air atmosphere.

[0011] To achieve this goal, this application adopts the following technical solutions:

[0012] In a first aspect, the present application provides a method for preparing a single-crystal lithium-rich manganese-based precursor, the preparation method comprising the following steps:

[0013] Under a protective atmosphere, a nickel-cobalt-manganese mixed salt solution, a precipitant, and a complexing agent are introduced into the base liquid to perform a coprecipitation reaction until D50 reaches a target particle size, and the solid-liquid is separated and dried to obtain the single crystal lithium-rich manganese-based precursor;

[0014] The precipitant is an alkaline solution, and the alkaline substance in the alkaline solution includes sodium hydroxide and / or potassium hydroxide;

[0015] The complexing agent is oxalic acid solution.

[0016] The preparation method provided in this application uses oxalic acid instead of conventional ammonia as a complexing agent, and utilizes oxalic acid and Mn 2+ The high complexation constant of oxalic acid allows the metal ions in the resulting lithium-rich manganese-based precursor to be mixed at the molecular level, with good contact between particles and uniform particle size. In addition, oxalic acid itself has reducing properties, so no additional reducing agent is required during the preparation process. After obtaining the lithium-rich manganese-based precursor, it is directly mixed with lithium carbonate and sintered in an air atmosphere to obtain a single-crystal lithium-rich manganese-based positive electrode material with excellent electrochemical properties and stable cycle performance. The sintering temperature is as low as 870°C, and the production cost is relatively low.

[0017] In one embodiment, the molar ratio of metal elements in the nickel-cobalt-manganese mixed salt solution is Ni:Co:Mn=x:y:z, wherein x+y+z=1, and z≥0.65, and can further be z≥0.7.

[0018] In the present application, the molar ratio of the metal elements in the nickel-cobalt-manganese mixed salt solution is Ni:Co:Mn=x:y:z, the values ​​of x, y and z are all positive numbers, and the values ​​of x and y are adjusted accordingly according to the value of z, and it is only necessary to satisfy the value of x+y+z=1.

[0019] The value of z satisfies z≥0.65, for example, it can be 0.65, 0.7, 0.75, 0.8, 0.85 or 0.9, but is not limited to the listed values. Other values ​​not listed in the numerical range are also applicable, and z≥0.7 can be further selected. That is, the preparation method provided by the present application utilizes oxalic acid and Mn 2+ The high complex constant makes it particularly suitable for the preparation of single-crystal lithium-rich manganese-based precursors with a high manganese content in nickel-cobalt-manganese.

[0020] In one embodiment, the metal salt in the nickel-cobalt-manganese mixed salt solution includes any one of sulfate, nitrate or chloride salts, or a combination of at least two of them. Typical but non-limiting combinations include a combination of sulfate and nitrate, a combination of nitrate and chloride, a combination of nitrate and chloride, or a combination of sulfate, nitrate and chloride.

[0021] The metal salts in the nickel-cobalt-manganese mixed salt solution of the present application include nickel salt, cobalt salt and manganese salt.

[0022] Exemplarily, the nickel salt includes any one or a combination of at least two of nickel nitrate, nickel sulfate or nickel chloride, typical but non-limiting combinations include a combination of nickel nitrate and nickel sulfate, a combination of nickel sulfate and nickel chloride, a combination of nickel nitrate and nickel chloride, or a combination of nickel nitrate, nickel sulfate and nickel chloride.

[0023] Exemplarily, the cobalt salt includes any one or a combination of at least two of cobalt nitrate, cobalt sulfate or cobalt chloride. Typical but non-limiting combinations include a combination of cobalt nitrate and cobalt sulfate, a combination of cobalt sulfate and cobalt chloride, a combination of cobalt nitrate and cobalt chloride, or a combination of cobalt nitrate, cobalt sulfate and cobalt chloride.

[0024] Exemplarily, the manganese salt includes any one or a combination of at least two of manganese nitrate, manganese sulfate or manganese chloride. Typical but non-limiting combinations include a combination of manganese nitrate and manganese sulfate, a combination of manganese sulfate and manganese chloride, a combination of manganese nitrate and manganese chloride, or a combination of manganese nitrate, manganese sulfate and manganese chloride.

[0025] In one embodiment, the mass concentration of the metal salt in the nickel-cobalt-manganese mixed salt solution is 90-100 g / L, for example, it can be 90 g / L, 92 g / L, 95 g / L, 96 g / L, 98 g / L or 100 g / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] In one embodiment, the mass fraction of the precipitant is 30-35wt%, for example, it can be 30wt%, 31wt%, 32wt%, 33wt%, 34wt% or 35wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] In one embodiment, the concentration of the complexing agent is 5-15 g / L, for example, 5 g / L, 8 g / L, 10 g / L, 12 g / L or 15 g / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Illustratively, the solvent of the oxalic acid solution described in the present application is water.

[0029] In one embodiment, the flow rate of the nickel-cobalt-manganese mixed salt solution is 1.2-1.6 kg / h, for example, it can be 1.2 kg / h, 1.3 kg / h, 1.4 kg / h, 1.5 kg / h or 1.6 kg / h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] In one embodiment, the flow rate of the complexing agent is 0.13-0.16 kg / h, for example, 0.13 kg / h, 0.14 kg / h, 0.15 kg / h or 0.16 kg / h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] In one embodiment, the flow rate of the precipitant is such that the pH value of the coprecipitation reaction is maintained at 10-11, for example, 10, 10.2, 10.5, 10.6, 10.8 or 11, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0032] If the flow rate of the precipitant makes the pH value of the coprecipitation reaction too high, the complexation effect of oxalic acid will be poor, and the OH in the solution will - It will compete for metal ions from the metal ion oxalate complex, resulting in too fast precipitation of metal ions. In addition, under high pH conditions, manganese hydroxide does not precipitate, but manganese oxide is preferentially generated. If the flow rate of the precipitant makes the pH value of the coprecipitation reaction too low, the metal ion precipitation will be incomplete, resulting in the loss of metal ions.

[0033] In one embodiment, the temperature of the coprecipitation reaction is 40-60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] In one embodiment, the coprecipitation reaction is carried out under stirring conditions.

[0035] If the temperature of the coprecipitation reaction is too high, the oxidation tendency of manganese will increase, and manganese will not precipitate in the form of hydroxide but will preferentially generate manganese oxide; when the reaction temperature is too low, the reaction rate will be slow, and there will be adsorption of impurity ions by the precipitate, which is not conducive to obtaining precursor particles with higher purity and larger particle size.

[0036] In one embodiment, the stirring speed is 300-700 rpm, for example, it can be 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm or 700 rpm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] In one embodiment, the base liquid is a combination of a precipitant, a complexing agent and water.

[0038] In one embodiment, the concentration of oxalic acid in the base liquid is 0.003-0.009wt%, for example, it can be 0.003wt%, 0.004wt%, 0.005wt%, 0.006wt%, 0.007wt%, 0.008wt% or 0.009wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] In one embodiment, the pH value of the base solution is 11.5-12.5, for example, it can be 11.5, 11.8, 12, 12.2 or 12.5, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0040] In one embodiment, the temperature of the base liquid is 40-60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0041] In one embodiment, the target particle size is 2-5 μm, for example, 2 μm, 3 μm, 4 μm or 5 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0042] In one embodiment, the solid-liquid separation method comprises sequentially performing filtration and washing.

[0043] The washing in this application is conventional washing in the art, and exemplary methods include but are not limited to alkaline solution washing and hot water washing.

[0044] In one embodiment, the drying temperature is 100-150°C, for example, 100°C, 110°C, 120°C, 130°C, 140°C or 150°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] In a second aspect, the present application provides a single-crystal lithium-rich manganese-based precursor, which is obtained by the preparation method described in the first aspect.

[0046] In a third aspect, the present application provides a single-crystal lithium-rich manganese-based positive electrode material, wherein the single-crystal lithium-rich manganese-based positive electrode material is prepared from the single-crystal lithium-rich manganese-based precursor of the second aspect.

[0047] Exemplarily, the method for preparing the single crystal lithium-rich manganese-based positive electrode material according to the third aspect of the present application comprises the following steps:

[0048] A single crystal lithium-rich manganese-based precursor is mixed with lithium carbonate and calcined under an air atmosphere to obtain the single crystal lithium-rich manganese-based positive electrode material.

[0049] Exemplarily, the calcination temperature is 870-930°C, for example, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C or 930°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0050] Exemplarily, the calcination time is ≥8 h, for example, 8 h, 10 h, 12 h, 14 h or 15 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0051] In a fourth aspect, the present application provides a lithium-ion battery, comprising the single-crystal lithium-rich manganese-based positive electrode material described in the third aspect.

[0052] Compared with the prior art, this application has the following beneficial effects:

[0053] The preparation method provided in this application uses oxalic acid instead of conventional ammonia as a complexing agent, and utilizes oxalic acid and Mn 2+ Due to the high complexation constant, the metal ions in the obtained lithium-rich manganese-based precursor can be mixed at the molecular level, with good contact between particles and uniform particle size. In addition, oxalic acid itself has reducing properties, and no additional reducing agent is required during the preparation process. After obtaining the lithium-rich manganese-based precursor, it is directly mixed with lithium carbonate and sintered in an air atmosphere to obtain a single-crystal lithium-rich manganese-based positive electrode material with excellent electrochemical properties and stable cycle performance. The sintering temperature is as low as 870°C, and the production cost is low.

[0054] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0056] FIG1 is a 10,000-fold SEM image of the single-crystalline lithium-rich manganese-based precursor obtained in Example 1;

[0057] Figure 2 is a 30,000x SEM image of the single-crystal lithium-rich manganese-based precursor obtained in Example 1

[0058] FIG3 is a 10,000-fold SEM image of the single-crystalline lithium-rich manganese-based positive electrode material obtained in Example 1;

[0059] FIG4 is a 30,000-fold SEM image of the single-crystalline lithium-rich manganese-based positive electrode material obtained in Example 1. DETAILED DESCRIPTION

[0060] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0061] Example 1

[0062] This embodiment provides a method for preparing a single-crystal lithium-rich manganese-based precursor, the preparation method comprising the following steps:

[0063] Under a nitrogen atmosphere and stirring at 500 rpm, a nickel-cobalt-manganese mixed salt solution, a precipitant, and a complexing agent were introduced into the base liquid, and a coprecipitation reaction was carried out at 50° C. until the D50 reached a target particle size of 4 μm. The product was filtered, washed three times with a saturated sodium hydroxide solution and three times with hot water, and dried at 120° C. to obtain the single crystal lithium-rich manganese-based precursor.

[0064] The mass concentration of the nickel-cobalt-manganese mixed salt solution is 95 g / L, wherein the metal salts are nickel sulfate, cobalt sulfate and manganese sulfate, and the molar ratio of the metal elements is Ni:Co:Mn=0.1:0.1:0.8;

[0065] The precipitant is an alkaline solution, and the alkaline substance in the alkaline solution is sodium hydroxide with a concentration of 32wt%;

[0066] The complexing agent is oxalic acid solution with a concentration of 10g / L;

[0067] The flow rate of the nickel-cobalt-manganese mixed salt solution is 1.5 kg / h, the flow rate of the complexing agent is 0.15 kg / h, and the flow rate of the precipitant is such that the pH value of the coprecipitation reaction is maintained at 10.5;

[0068] The base liquid is a combination of a precipitant, a complexing agent and water, the concentration of oxalic acid in the base liquid is 0.005 wt %, the pH value is 12, and the temperature is 50° C.;

[0069] The SEM images of the single-crystalline lithium-rich manganese-based precursor obtained in this embodiment are shown in Figures 1 and 2. It can be seen from Figures 1 and 2 that the preparation method provided in this embodiment can mix the metal ions in the lithium-rich manganese-based precursor at the molecular level, and the particles have good contact and uniform particle size.

[0070] The single-crystal lithium-rich manganese-based precursor prepared in this example was mixed with lithium carbonate and calcined at 900° C. for 10 h in air atmosphere to obtain a single-crystal lithium-rich manganese-based positive electrode material, whose SEM images are shown in FIG3 and FIG4 .

[0071] Example 2

[0072] This embodiment provides a method for preparing a single-crystal lithium-rich manganese-based precursor, the preparation method comprising the following steps:

[0073] Under a nitrogen atmosphere and stirring at 300 rpm, a nickel-cobalt-manganese mixed salt solution, a precipitant, and a complexing agent were introduced into the base liquid, and a coprecipitation reaction was carried out at 40° C. until the D50 reached a target particle size of 5 μm. The product was filtered, washed three times with a saturated sodium hydroxide solution and three times with hot water, and dried at 100° C. to obtain the single crystal lithium-rich manganese-based precursor.

[0074] The mass concentration of the nickel-cobalt-manganese mixed salt solution is 90 g / L, wherein the metal salts are nickel sulfate, cobalt sulfate and manganese sulfate, and the molar ratio of the metal elements is Ni:Co:Mn=0.1:0.1:0.8;

[0075] The precipitant is an alkaline solution, and the alkaline substance in the alkaline solution is sodium hydroxide with a concentration of 30wt%;

[0076] The complexing agent is oxalic acid solution with a concentration of 5g / L;

[0077] The flow rate of the nickel-cobalt-manganese mixed salt solution is 1.6 kg / h, the flow rate of the complexing agent is 0.16 kg / h, and the flow rate of the precipitant is such that the pH value of the coprecipitation reaction is maintained at 10;

[0078] The base liquid is a combination of a precipitant, a complexing agent and water, the concentration of oxalic acid in the base liquid is 0.003 wt %, the pH value is 11.5, and the temperature is 40° C.;

[0079] The preparation method provided in this embodiment can achieve molecular-level mixing of metal ions in the lithium-rich manganese-based precursor, with good contact between particles and uniform particle size.

[0080] The single-crystal lithium-rich manganese-based precursor prepared in this example was mixed with lithium carbonate and calcined at 900° C. for 10 h in an air atmosphere to obtain a single-crystal lithium-rich manganese-based positive electrode material.

[0081] Example 3

[0082] This embodiment provides a method for preparing a single-crystal lithium-rich manganese-based precursor, the preparation method comprising the following steps:

[0083] Under a nitrogen atmosphere and stirring at 700 rpm, a nickel-cobalt-manganese mixed salt solution, a precipitant, and a complexing agent were introduced into the base liquid, and a coprecipitation reaction was carried out at 60° C. until the D50 reached a target particle size of 2 μm. The product was filtered, washed three times with a saturated sodium hydroxide solution and hot water, respectively, and dried at 150° C. to obtain the single crystal lithium-rich manganese-based precursor.

[0084] The mass concentration of the nickel-cobalt-manganese mixed salt solution is 100 g / L, wherein the metal salts are nickel sulfate, cobalt sulfate and manganese sulfate, and the molar ratio of the metal elements is Ni:Co:Mn=0.1:0.1:0.8;

[0085] The precipitant is an alkaline solution, and the alkaline substance in the alkaline solution is sodium hydroxide with a concentration of 35wt%;

[0086] The complexing agent is oxalic acid solution with a concentration of 15g / L;

[0087] The flow rate of the nickel-cobalt-manganese mixed salt solution is 1.2 kg / h, the flow rate of the complexing agent is 0.13 kg / h, and the flow rate of the precipitant is such that the pH value of the coprecipitation reaction is maintained at 11;

[0088] The base liquid is a combination of a precipitant, a complexing agent and water, the concentration of oxalic acid in the base liquid is 0.009 wt %, the pH value is 12.5, and the temperature is 60° C.;

[0089] The preparation method provided in this embodiment can achieve molecular-level mixing of metal ions in the lithium-rich manganese-based precursor, with good contact between particles and uniform particle size.

[0090] The single-crystal lithium-rich manganese-based precursor prepared in this example was mixed with lithium carbonate and calcined at 900° C. for 10 h in an air atmosphere to obtain a single-crystal lithium-rich manganese-based positive electrode material.

[0091] Example 4

[0092] This embodiment provides a method for preparing a single-crystal lithium-rich manganese-based precursor, and the process steps of the preparation method are the same as those of Example 1.

[0093] The single-crystalline lithium-rich manganese-based precursor prepared in this example was mixed with lithium carbonate and calcined at 870° C. for 12 h in an air atmosphere to obtain a single-crystalline lithium-rich manganese-based positive electrode material.

[0094] Example 5

[0095] This embodiment provides a method for preparing a single-crystal lithium-rich manganese-based precursor, and the process steps of the preparation method are the same as those of Example 1.

[0096] The single-crystal lithium-rich manganese-based precursor prepared in this example was mixed with lithium carbonate and calcined at 930° C. for 8 h in an air atmosphere to obtain a single-crystal lithium-rich manganese-based positive electrode material.

[0097] Example 6

[0098] This embodiment provides a method for preparing a single-crystal lithium-rich manganese-based precursor, which is the same as Example 1 except that the molar ratio of the metal elements in the nickel-cobalt-manganese mixed salt solution is Ni:Co:Mn=0.2:0.1:0.7.

[0099] The single-crystal lithium-rich manganese-based precursor prepared in this example was mixed with lithium carbonate and calcined at 900° C. for 10 h in an air atmosphere to obtain a single-crystal lithium-rich manganese-based positive electrode material.

[0100] Example 7

[0101] This embodiment provides a method for preparing a single-crystal lithium-rich manganese-based precursor, which is the same as Example 1 except that the molar ratio of the metal elements in the nickel-cobalt-manganese mixed salt solution is Ni:Co:Mn=0.25:0.1:0.65.

[0102] The single-crystal lithium-rich manganese-based precursor prepared in this example was mixed with lithium carbonate and calcined at 900° C. for 10 h in an air atmosphere to obtain a single-crystal lithium-rich manganese-based positive electrode material.

[0103] Example 8

[0104] This embodiment provides a method for preparing a single-crystal lithium-rich manganese-based precursor, which is the same as Example 1 except that the molar ratio of the metal elements in the nickel-cobalt-manganese mixed salt solution is Ni:Co:Mn=0.3:0.1:0.6.

[0105] The single-crystal lithium-rich manganese-based precursor prepared in this example was mixed with lithium carbonate and calcined at 900° C. for 10 h in an air atmosphere to obtain a single-crystal lithium-rich manganese-based positive electrode material.

[0106] Example 9

[0107] This embodiment provides a method for preparing a single-crystal lithium-rich manganese-based precursor. Except for controlling the flow rate of the precipitant to maintain the pH value of the co-precipitation reaction at 10.5, the rest is the same as that of Example 1.

[0108] The single-crystal lithium-rich manganese-based precursor prepared in this example was mixed with lithium carbonate and calcined at 900° C. for 10 h in an air atmosphere to obtain a single-crystal lithium-rich manganese-based positive electrode material.

[0109] Example 10

[0110] This embodiment provides a method for preparing a single-crystal lithium-rich manganese-based precursor. Except for controlling the flow rate of the precipitant to maintain the pH value of the co-precipitation reaction at 11.5, the rest is the same as that of Example 1.

[0111] The single-crystal lithium-rich manganese-based precursor prepared in this example was mixed with lithium carbonate and calcined at 900° C. for 10 h in an air atmosphere to obtain a single-crystal lithium-rich manganese-based positive electrode material.

[0112] Comparative Example 1

[0113] This comparative example provides a method for preparing a single-crystal lithium-rich manganese-based precursor, which is the same as Example 1 except that the complexing agent introduced during the coprecipitation reaction is replaced by ammonia water of equal concentration.

[0114] The single-crystal lithium-rich manganese-based precursor prepared in this comparative example was mixed with lithium carbonate and calcined at 900° C. for 10 h in an air atmosphere to obtain a single-crystal lithium-rich manganese-based positive electrode material.

[0115] Comparative Example 2

[0116] This comparative example provides a method for preparing a single-crystal lithium-rich manganese-based precursor, which is the same as Example 1 except that the mass of the complexing agent in the base liquid is replaced by ammonia water, and the complexing agent introduced during the coprecipitation reaction is replaced by ammonia water of the same concentration.

[0117] The single-crystal lithium-rich manganese-based precursor prepared in this comparative example was mixed with lithium carbonate and calcined at 900° C. for 10 h in an air atmosphere to obtain a single-crystal lithium-rich manganese-based positive electrode material.

[0118] Performance Characterization

[0119] The single crystal lithium-rich manganese-based positive electrode materials obtained in each embodiment and comparative example are prepared into lithium-ion batteries by the following preparation method:

[0120] Single-crystal lithium-rich manganese-based positive electrode material, binder polyvinylidene fluoride, and conductive agent Super P were added to N-methylpyrrolidone at a mass ratio of 80:5:5 and stirred to form a positive electrode slurry; the positive electrode slurry was then evenly coated on the positive electrode current collector aluminum foil, dried and rolled to obtain a positive electrode sheet;

[0121] The lithium sheet, separator, electrolyte (the electrolyte is 5V high-voltage electrolyte) and positive electrode sheet are assembled in sequence, and the battery model is a 2032 battery shell to obtain a lithium-ion button battery.

[0122] The specific capacity and cycle capacity retention rate of the obtained lithium-ion button battery were tested, and the results are shown in Table 1.

[0123] The specific capacity test method is as follows: using the Blue Power Battery Test System, at 25°C, the lithium-ion battery is charged and discharged three times in the voltage range of 2V to 4.6V at a charge and discharge rate of 0.1C (1C = 250mAh / g) to measure the battery specific capacity;

[0124] The test method for cycle capacity retention is as follows: the button battery is charged and discharged in the voltage range of 2.0 to 4.6V. Before the cycle test, it is activated three times with a small current density of 0.1C. At 25°C, the charge and discharge mode is 0.1C. After 100 cycles, the discharge capacity of the battery at this time is divided by the discharge capacity of the first cycle, which is the battery's 100-cycle capacity retention rate.

[0125] Charge and discharge testing: The button-type battery was charged and discharged over a voltage range of 2.0-4.6V. Prior to cycling testing, the battery was activated three times at a low current density of 0.1C. Subsequently, discharge was performed over the same voltage range at current densities of 25mA / g, 50mA / g, 125mA / g, 250mA / g (1C), 500mA / g, 1250mA / g, and 2500mA / g, with a charge current density of 25mA / g. All electrochemical performance tests were conducted at room temperature.

[0126] Table 1

[0127] In summary, the preparation method provided by this application uses oxalic acid instead of conventional ammonia as a complexing agent, and utilizes oxalic acid and Mn 2+ Due to the high complexation constant, the metal ions in the obtained lithium-rich manganese-based precursor can be mixed at the molecular level, with good contact between particles and uniform particle size. In addition, oxalic acid itself has reducing properties, and no additional reducing agent is required during the preparation process. After obtaining the lithium-rich manganese-based precursor, it is directly mixed with lithium carbonate and sintered in an air atmosphere to obtain a single-crystal lithium-rich manganese-based positive electrode material with excellent electrochemical properties and stable cycle performance. The sintering temperature is as low as 870°C, and the production cost is low.

[0128] The above description is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Those skilled in the art should understand that any changes or replacements that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for preparing a single-crystal lithium-rich manganese-based precursor, the preparation method comprising the following steps: Under a protective atmosphere, a nickel-cobalt-manganese mixed salt solution, a precipitant and a complexing agent are introduced into the base liquid to perform a coprecipitation reaction until D50 reaches a target particle size, and the solid-liquid is separated and dried to obtain the single crystal lithium-rich manganese-based precursor; The precipitant is an alkaline solution, and the alkaline substance in the alkaline solution includes sodium hydroxide and / or potassium hydroxide; The complexing agent is oxalic acid solution.

2. The preparation method according to claim 1, wherein The molar ratio of metal elements in the nickel-cobalt-manganese mixed salt solution is Ni:Co:Mn=x:y:z, wherein x+y+z=1, and z≥0.65; Optionally, z ≥ 0.7; Optionally, the metal salt in the nickel-cobalt-manganese mixed salt solution includes any one of sulfate, nitrate or chloride, or a combination of at least two thereof; Optionally, the mass concentration of the metal salt in the nickel-cobalt-manganese mixed salt solution is 90-100 g / L.

3. The preparation method according to claim 1 or 2, wherein The mass fraction of the precipitant is 30-35wt%; Optionally, the concentration of the complexing agent is 5-15 g / L.

4. The preparation method according to any one of claims 1 to 3, wherein: The flow rate of the nickel-cobalt-manganese mixed salt solution is 1.2-1.6 kg / h; Optionally, the complexing agent has an inlet flow rate of 0.13-0.16 kg / h; Optionally, the precipitant is introduced at a flow rate such that the pH value of the coprecipitation reaction is maintained at 10-11; Optionally, the coprecipitation reaction temperature is 40-60°C.

5. The preparation method according to any one of claims 1 to 4, wherein: The coprecipitation reaction is carried out under stirring; Optionally, the stirring speed is 300-700 rpm.

6. The preparation method according to any one of claims 1 to 5, wherein: The base liquid is a combination of a precipitant, a complexing agent and water; Optionally, the concentration of oxalic acid in the base solution is 0.003-0.009wt%; Optionally, the pH value of the base solution is 11.5-12.5; Optionally, the temperature of the base liquid is 40-60°C.

7. The preparation method according to any one of claims 1 to 6, wherein: The target particle size is 2-5 μm; Optionally, the solid-liquid separation method comprises sequentially performing suction filtration and washing; Optionally, the drying temperature is 100-150°C.

8. A single-crystal lithium-rich manganese-based precursor, wherein the single-crystal lithium-rich manganese-based precursor is obtained by the preparation method according to any one of claims 1 to 7.

9. A single crystal lithium-rich manganese-based positive electrode material, wherein the single crystal lithium-rich manganese-based positive electrode material is prepared from the single crystal lithium-rich manganese-based precursor according to claim 8.

10. A lithium-ion battery, comprising the lithium-rich manganese-based positive electrode material according to claim 9.

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