Iron-doped lithium-rich manganese-based precursor material, preparation method therefor and use thereof

Abstract

The present application provides an iron-doped lithium-rich manganese-based precursor material, a preparation method therefor, and a use thereof. The iron-doped lithium-rich manganese-based precursor material comprises a lithium-rich manganese-based precursor base material and iron element doped on a surface layer of the lithium-rich manganese-based precursor base material. The preparation method comprises the following steps: in a protective atmosphere, concurrently adding a main metal source mixed salt solution, a precipitant solution, and a first complexing agent solution for a first stage of co-precipitation reaction, and then adding an iron source solution to continue a second stage of co-precipitation reaction to obtain the iron-doped lithium-rich manganese-based precursor material. In the present application, after the surface layer of the lithium-rich manganese-based precursor base material is doped with iron to further prepare a positive electrode material, the iron element therein is converted into TMFe2O4 (TM is a main metal element), so that the electrochemical performance of a lithium-rich manganese-based positive electrode material is improved.

Description

An iron-doped lithium-rich manganese-based precursor material and its preparation method and use Technical Field

[0001] The present application belongs to the technical field of lithium-ion batteries and relates to an iron-doped lithium-rich manganese-based precursor material and a preparation method and use thereof. Background Art

[0002] In recent years, the application areas of lithium-ion batteries have continued to expand, from traditional 3C products to current electric vehicles and smart grids. The new energy industry has an increasingly urgent demand for lithium-ion batteries, especially high-energy-density lithium batteries. To meet this demand, a large amount of research has been devoted to the development of electrode materials with high specific capacity. The lithium-rich manganese-based cathode material aLi2MnO3·(1-a)LiMO2 (M = one or more of Ni, Co, Mn, Al, V, Cr, Fe) has a discharge capacity exceeding 250mAh / g and an operating voltage greater than 3.50V. Due to its high specific capacity, good thermal stability, excellent cycle performance, wide charge and discharge voltage range, low price, and environmental friendliness, it has attracted in-depth research from many experts and scholars in the industry and has great development potential.

[0003] Although lithium-rich manganese-based positive electrode materials have a high specific capacity of more than 250mAh / g, there are still many problems in their application in actual production, including low first efficiency (about 75%) and obvious voltage and capacity attenuation during the cycle. At present, the first efficiency can be increased to 85% or close to 90% through surface coating modification or special surface activation process. The problem of rapid voltage and capacity attenuation during the cycle is mainly due to the side reaction between the material and the electrolyte caused by high voltage, and the breakage, pulverization and detachment of the agglomerate particles during the cycle, which causes the exposed fresh internal surface to continue to react with the electrolyte and lead to the formation of other phases, resulting in the deterioration of voltage and capacity.

[0004] In CN112701273B, fluoride ion doping is achieved by soluble fluoride salts, and the electronegativity of fluorine is used to suppress the release of oxygen, thereby improving the cycle stability. In CN113788500A, the sintered lithium-rich manganese-based material is mixed with a stannous salt solution and stirred. After sintering, a surface coated with a double layer of spinel phase layer and SnO2 layer with oxygen vacancies is obtained. Due to the presence of oxygen vacancies, the release of oxygen is effectively suppressed, so that the positive electrode material has a higher first-cycle coulomb efficiency, discharge capacity, cycle stability and rate performance. The current mainstream modification methods are to modify the material based on the sintered finished product. Although it can improve the performance of the material to a certain extent, it cannot change the fact that the lithium-rich manganese-based material is structurally unstable and easy to pulverize. In addition, the structure of the lithium-ion battery prepared from the existing lithium-rich manganese-based material in the cycle process is unstable and the production cost is high.

[0005] Therefore, how to solve the problem of rapid capacity decay during the lithium-rich manganese-based cycle is currently urgently needed.

[0006] Summary of the Invention

[0007] 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.

[0008] The present application provides an iron-doped lithium-rich manganese-based precursor material, its preparation method, and its use. The present application further prepares a positive electrode material by doping the surface layer of the lithium-rich manganese-based precursor matrix with iron, wherein the iron element is converted into TMFe2O4 (TM is the main metal element), thereby improving the electrochemical performance of the lithium-rich manganese-based positive electrode material.

[0009] In a first aspect, the present application provides an iron-doped lithium-rich manganese-based precursor material, wherein the iron-doped lithium-rich manganese-based precursor material comprises a lithium-rich manganese-based precursor matrix material and iron elements doped in the surface layer of the lithium-rich manganese-based precursor matrix material.

[0010] In this application, iron is doped into the surface layer of a lithium-rich manganese-based precursor matrix material, and the iron is evenly distributed in the surface layer. After further preparation of the positive electrode material, the iron element therein is converted into TMFe2O4 (TM is the main metal element), thereby improving the electrochemical performance of the lithium-rich manganese-based positive electrode material.

[0011] In the present application, iron is doped only on the surface of the lithium-rich manganese-based precursor matrix material, which can form a protective layer on the surface of the lithium-rich manganese-based material, thereby improving the cycle performance of the lithium-rich manganese-based material; if the entire precursor matrix material is doped with iron, it will lead to an excessively high proportion of Fe elements, thereby reducing the material capacity; at the same time, if iron is directly doped in the positive electrode material, it cannot achieve uniform doping of Fe elements, and the protective layer formed has poor bonding strength; and if iron is not doped, the problem of surface stability of the lithium-rich manganese-based material cannot be solved.

[0012] In one embodiment, the chemical formula of the lithium-rich manganese-based precursor matrix material is Mn x M y (OH)2, wherein M includes a transition metal element, 0<x<1, 0<y<1, and x+y=1, for example, the x can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, etc., and the y can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, etc.

[0013] In one embodiment, the M comprises Ni and / or Co.

[0014] In a second aspect, the present application provides a method for preparing the iron-doped lithium-rich manganese-based precursor material as described in the first aspect, the preparation method comprising the following steps:

[0015] Under a protective atmosphere, the main metal source mixed salt solution, the precipitant solution and the first complexing agent solution are added in parallel to carry out a first-stage coprecipitation reaction, and then the iron source solution is added to continue the second-stage coprecipitation reaction to obtain the iron-doped lithium-rich manganese-based precursor material.

[0016] The preparation method provided in this application is a preparation of a pure lithium-rich manganese-based precursor matrix material in the first stage. After the first stage, an iron source is further added on the basis of the original preparation to carry out a co-precipitation reaction in the second stage to achieve surface iron doping. At the same time, an iron-based lithium-rich manganese-based precursor material is obtained in the second stage, that is, iron is evenly distributed on the surface of the matrix material. The preparation method is simple, does not require a complicated preparation process, and is suitable for large-scale production.

[0017] In one embodiment, the concentration of the main metal source mixed salt solution is 2 to 4 mol / L, for example, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L.

[0018] In one embodiment, in the main metal source mixed salt solution, the molar ratio of nickel, cobalt and manganese elements is (0.2-0.4):(0-0.1):(0.5-0.75).

[0019] In one embodiment, the precipitant solution comprises sodium hydroxide solution.

[0020] In one embodiment, the first complexing agent solution includes any one of an aqueous ammonia solution, an oxalic acid solution, or a sodium oxalate solution, or a combination of at least two thereof.

[0021] In one embodiment, the temperature of the first stage coprecipitation reaction is 25-80°C, for example, 25°C, 30°C, 40°C, 50°C, 60°C, 70°C or 80°C.

[0022] In one embodiment, the rotation speed of the coprecipitation reaction in the first stage is 200-400 r / min, for example, 200 r / min, 230 r / min, 250 r / min, 280 r / min, 300 r / min, 330 r / min, 350 r / min, 380 r / min or 400 r / min.

[0023] In one embodiment, the pH of the coprecipitation reaction in the first stage is 10-12, for example, 10, 10.3, 10.5, 10.8, 11, 11.3, 11.5, 11.8 or 12.

[0024] In one embodiment, the reaction time of the first stage coprecipitation reaction accounts for 88-91% of the total reaction time during the coprecipitation reaction, such as 88%, 88.5%, 89%, 89.5%, 90%, 90.5% or 91%.

[0025] In the present application, the total reaction time in the co-precipitation reaction process is the sum of the reaction time of the co-precipitation reaction in the first stage and the reaction time of the co-precipitation reaction in the second stage; if the reaction time in the first stage accounts for too little, it will lead to excessive iron doping, which is not only distributed on the surface, thereby affecting the final capacity of the material; and if the reaction time in the first stage accounts for too much, it will lead to too little iron doping, which is not conducive to the formation of an effective protective layer.

[0026] In one embodiment, the reaction time of the first stage coprecipitation reaction is 50 to 100 h, for example, 50 h, 55 h, 60 h, 65 h, 70 h, 75 h, 80 h, 85 h, 90 h, 95 h or 100 h.

[0027] In one embodiment, the temperature of the second stage coprecipitation reaction is 25-80°C, such as 25°C, 30°C, 40°C, 50°C, 60°C, 70°C or 80°C.

[0028] In one embodiment, the rotation speed of the coprecipitation reaction in the second stage is 200-400 r / min, for example, 200 r / min, 230 r / min, 250 r / min, 280 r / min, 300 r / min, 330 r / min, 350 r / min, 380 r / min or 400 r / min.

[0029] In one embodiment, the reaction time of the second stage coprecipitation reaction is 5 to 15 hours, for example, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours or 15 hours.

[0030] In one embodiment, a second complexing agent solution is added simultaneously with the addition of the iron source.

[0031] In the present application, a second complexing agent solution is added at the same time as the iron source is added. The second complexing agent solution plays the role of adjusting the co-precipitation parameters, thereby realizing the co-complexation of iron and the main metal element. If the second complexing agent solution is not added, it will be difficult to achieve the co-precipitation of iron and the main metal element, resulting in phase separation precipitation of the Fe element and even the production of Fe(OH)3 colloid, which affects the stability of the reaction system.

[0032] In one embodiment, the iron source solution comprises a ferrous salt solution.

[0033] In the present application, no additional reducing agent is required, and the entire reaction process is carried out in a protective atmosphere (such as nitrogen atmosphere and / or inert atmosphere).

[0034] In one embodiment, the concentration of the second complexing agent solution is 0.1 to 0.3 mol / L, such as 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L or 0.3 mol / L.

[0035] In the present application, if the concentration of the second complexing agent solution is too low, it will be unfavorable for the complexation of Fe; and if it is too high, it will make it difficult for Fe to precipitate.

[0036] In one embodiment, the second complexing agent solution includes any one of citric acid solution, sodium citrate solution, lactic acid solution or tartaric acid solution, or a combination of at least two thereof.

[0037] In the present application, the second complexing agent solution is selected from the above substances, which can better achieve co-precipitation of Fe and the main metal element.

[0038] As an optional technical solution, the preparation method includes the following steps:

[0039] Under a protective atmosphere, a main metal source mixed salt solution, a precipitant solution, and a first complexing agent solution are added in parallel to perform a first-stage coprecipitation reaction, and then an iron source solution and a second complexing agent solution with a concentration of 0.1 to 0.3 mol / L are added to continue the second-stage coprecipitation reaction to obtain the iron-doped lithium-rich manganese-based precursor material;

[0040] The first complexing agent solution includes any one of ammonia solution, oxalic acid solution or sodium oxalate solution, or a combination of at least two of them; the second complexing agent solution includes any one of citric acid solution, sodium citrate solution, lactic acid solution or tartaric acid solution, or a combination of at least two of them; and the reaction time of the coprecipitation reaction in the first stage accounts for 88 to 91% of the total reaction time in the coprecipitation reaction process.

[0041] It should be noted that, in this application, before adding the raw materials in parallel, a base liquid may be added first. The base liquid may be pure water or a prepared liquid.

[0042] Illustratively, the present application provides a base liquid, which is a mixed solution of water, a precipitant solution and a first complexing agent solution; the pH value of the base liquid is 10 to 12.0; the concentration of the first complexing agent solution is 0.1 to 0.3 mol / L; those skilled in the art can adaptively adjust and select according to actual needs.

[0043] In the third aspect, the present application provides an iron-doped lithium-rich manganese-based positive electrode material, wherein the iron-doped lithium-rich manganese-based positive electrode material is obtained by mixing and sintering the precursor material as described in the first aspect with a lithium source; the iron-doped lithium-rich manganese-based positive electrode material includes a lithium-rich manganese-based positive electrode matrix material and a protective layer of TMFe2O4 phase structure on the surface of the lithium-rich manganese-based positive electrode matrix material, wherein TM is the main metal element in the lithium-rich manganese-based positive electrode matrix material.

[0044] The preparation methods of the lithium-rich manganese-based positive electrode materials provided in this application are all conventional technical means. Those skilled in the art can adaptively adjust the type of lithium source, sintering steps and parameters according to actual needs. The sintering process can be carried out only once or in steps.

[0045] At the same time, the molar ratio of lithium in the lithium source to the sum of the main metal elements in the iron-doped lithium-rich manganese-based precursor material is (1.25-1.4):1.

[0046] In a fourth aspect, the present application further provides a lithium-ion battery, which comprises the iron-doped lithium-rich manganese-based positive electrode material as described in the third aspect.

[0047] Compared with the related art, this application has the following beneficial effects:

[0048] (1) The present application achieves improved electrochemical performance of the lithium-rich manganese-based positive electrode material by doping the surface layer of the lithium-rich manganese-based precursor matrix material with iron, wherein the iron is evenly distributed in the surface layer. After further preparing the positive electrode material, the iron element and the main metal element are transformed into a TMFe2O4 phase structure (TM is the main metal element), forming a uniform protective layer.

[0049] (2) The preparation method provided in the present application is a preparation of a pure lithium-rich manganese-based precursor matrix material in the first stage. After the first stage, an iron source is further added on the basis of the original preparation to carry out a co-precipitation reaction in the second stage, thereby achieving surface iron doping. At the same time, an iron-based lithium-rich manganese-based precursor material is obtained in the second stage, that is, iron is evenly distributed on the surface of the matrix material. The preparation method is simple, does not require a complicated preparation process, and is suitable for large-scale production.

[0050] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0051] The technical solution of the present application is further illustrated below by specific examples. Those skilled in the art should understand that the examples are only for facilitating understanding of the present application and should not be regarded as specific limitations of the present application.

[0052] Example 1

[0053] This embodiment provides an iron-doped lithium-rich manganese-based precursor material, which includes a lithium-rich manganese-based precursor matrix material and iron elements doped in the surface layer of the lithium-rich manganese-based precursor matrix material; the chemical formula of the lithium-rich manganese-based precursor matrix material is Ni 0.375 Mn 0.625 (OH)2.

[0054] The preparation method of the iron-doped lithium-rich manganese-based precursor material is as follows:

[0055] Nickel sulfate and manganese sulfate were weighed according to the stoichiometric ratio of Ni:Mn=37.5:62.5 to prepare a 2 mol / L mixed salt solution; the mixed salt solution, 2 mol / L sodium hydroxide solution, and 0.1 mol / L ammonia solution were added to the bottom liquid of the reactor (water, sodium hydroxide, and ammonia solution were used as the bottom liquid to make its pH value 11.5-11.8, the concentration of ammonia solution was 0.3 mol / L, N2 was introduced, and the temperature was controlled at 40°C), and the mixture was continuously stirred at a speed of 400 r / min to maintain the pH of the reaction system at 10.0-10.5 for the first stage of coprecipitation reaction. After the reaction for 80 hours, 0.1 mol / L ferrous sulfate solution and 0.1 mol / L sodium citrate solution (second complexing agent solution) were additionally added in parallel and the reaction was continued for 10 hours before the reaction was terminated (second stage coprecipitation reaction). After washing, drying, and sieving, Ni-doped with Fe on the surface was obtained. 0.375 Mn 0.625 (OH)2-like spherical lithium-rich manganese-based precursor material;

[0056] Nitrogen was introduced during the entire reaction process. The reaction time of the first stage co-precipitation reaction accounted for 88.9% of the total reaction time of the precipitation process.

[0057] This embodiment also provides a lithium-rich manganese-based positive electrode material, which is prepared from the precursor material prepared above. The specific preparation method is as follows:

[0058] The obtained precursor material was mixed with LiOH in a stoichiometric ratio of Me:Li=1:1.3, and then heated to 800℃, kept at this temperature for 10h, and then cooled in the furnace to obtain a spherical iron-doped lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.3 Mn 0.5 O2, among which the surface doped Fe and the main metal element form a TMFe2O4 phase structure (TM is the main metal element), which plays a protective role.

[0059] Example 2

[0060] This embodiment provides an iron-doped lithium-rich manganese-based precursor material, which includes a lithium-rich manganese-based precursor matrix material and iron elements doped in the surface layer of the lithium-rich manganese-based precursor matrix material; the chemical formula of the lithium-rich manganese-based precursor matrix material is Ni 0.375 Mn 0.625 (OH)2.

[0061] The preparation method of the iron-doped lithium-rich manganese-based precursor material is as follows:

[0062] Nickel sulfate and manganese sulfate were weighed according to the stoichiometric ratio of Ni:Mn=37.5:62.5 to prepare a 2 mol / L mixed salt solution; the mixed salt solution, 2 mol / L sodium hydroxide solution, and 0.1 mol / L ammonia solution were added to the bottom liquid of the reactor (water, sodium hydroxide, and ammonia solution were used as the bottom liquid to make its pH value 11.5-11.8, the concentration of ammonia solution was 0.3 mol / L, N2 was introduced, and the temperature was controlled at 40°C), and the mixture was continuously stirred at a speed of 350 r / min to maintain the pH of the reaction system at 10.0-10.5 for the first stage of coprecipitation reaction. After the reaction for 90 hours, 0.1 mol / L ferrous sulfate solution and 0.2 mol / L citric acid solution (second complexing agent solution) were additionally added in parallel and the reaction was continued for 10 hours before the reaction was terminated (second stage coprecipitation reaction). After washing, drying, and sieving, Ni-doped with Fe on the surface was obtained. 0.375 Mn 0.625 (OH)2-like spherical lithium-rich manganese-based precursor material;

[0063] Nitrogen was introduced throughout the entire reaction process. The reaction time of the first stage coprecipitation reaction accounted for 90% of the total reaction time of the total precipitation process (first stage plus second stage).

[0064] This embodiment also provides a lithium-rich manganese-based positive electrode material, which is prepared from the precursor material prepared above. The specific preparation method is as follows:

[0065] The obtained precursor material was mixed with LiOH in a stoichiometric ratio of Me:Li=1:1.3, and then heated to 800℃, kept at this temperature for 10h, and then cooled in the furnace to obtain a spherical iron-doped lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.3 Mn 0.5 O2, among which the surface doped Fe and the main metal element form a TMFe2O4 phase structure (TM is the main metal element), which plays a protective role.

[0066] Example 3

[0067] This embodiment provides an iron-doped lithium-rich manganese-based precursor material, which includes a lithium-rich manganese-based precursor matrix material and iron elements doped in the surface layer of the lithium-rich manganese-based precursor matrix material; the chemical formula of the lithium-rich manganese-based precursor matrix material is Ni 0.375 Mn 0.625 (OH)2.

[0068] The preparation method of the iron-doped lithium-rich manganese-based precursor material is as follows:

[0069] Nickel sulfate and manganese sulfate were weighed according to the stoichiometric ratio of Ni:Mn=37.5:62.5 to prepare a 3 mol / L mixed salt solution; the mixed salt solution, 2 mol / L sodium hydroxide solution, and 0.1 mol / L ammonia solution were added to the bottom liquid of the reactor (water, sodium hydroxide, and ammonia solution were used as the bottom liquid to make its pH value 11.3-11.5, the concentration of ammonia solution was 0.3 mol / L, N2 was introduced, and the temperature was controlled at 40°C), and the mixture was continuously stirred at a speed of 300 r / min to maintain the pH of the reaction system at 10.0-10.5 for the first stage of coprecipitation reaction. After the reaction was carried out for 100 h, 0.1 mol / L ferrous sulfate solution and 0.3 mol / L lactic acid solution (second complexing agent solution) were additionally added in parallel to continue the reaction for 10 h before terminating the reaction (second stage coprecipitation reaction). After washing, drying, and sieving, Ni-doped with Fe on the surface was obtained. 0.375 Mn 0.625 (OH)2-like spherical lithium-rich manganese-based precursor material;

[0070] Nitrogen was introduced during the entire reaction process. The reaction time of the first stage coprecipitation reaction accounted for 90.9% of the total reaction time of the precipitation process.

[0071] This embodiment also provides a lithium-rich manganese-based positive electrode material, which is prepared from the precursor material prepared above. The specific preparation method is as follows:

[0072] The obtained precursor material was mixed with LiOH in a stoichiometric ratio of Me:Li=1:1.3, and then heated to 800℃, kept at this temperature for 10h, and then cooled in the furnace to obtain a spherical iron-doped lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.3 Mn 0.5 O2, among which the surface doped Fe and the main metal element form a TMFe2O4 phase structure (TM is the main metal element), which plays a protective role.

[0073] Example 4

[0074] The difference between this embodiment and embodiment 1 is that the chemical formula of the lithium-rich manganese-based precursor matrix material in this embodiment is Ni 0.2 Co 0.1Mn 0.7 (OH)2.

[0075] In the preparation method, nickel sulfate, manganese sulfate and cobalt sulfate are weighed according to the stoichiometric ratio of Ni:Co:Mn=0.20.1:0.7 to prepare a 2 mol / L mixed salt solution.

[0076] The rest of the preparation methods and parameters were the same as those in Example 1.

[0077] The obtained precursor material was mixed with LiOH in a stoichiometric ratio of Me:Li=1:1.3, and then heated to 800℃, kept at this temperature for 10h, and then cooled in the furnace to obtain a spherical iron-doped lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.16 Co 0.08 Mn 0.56 O2, among which the surface doped Fe and the main metal element form a TMFe2O4 phase structure (TM is the main metal element), which plays a protective role.

[0078] Example 5

[0079] The difference between this embodiment and Example 1 is that the reaction time of the coprecipitation reaction in the first stage of this embodiment is 60 hours; that is, nitrogen is introduced throughout the reaction process, and the reaction time of the coprecipitation reaction in the first stage accounts for 85.7% of the total reaction time of the total precipitation process (first stage plus second stage).

[0080] Example 6

[0081] The difference between this embodiment and Example 1 is that the reaction time of the coprecipitation reaction in the first stage of this embodiment is 120 hours; that is, nitrogen is introduced throughout the reaction process, and the reaction time of the coprecipitation reaction in the first stage accounts for 92.3% of the total reaction time of the total precipitation process (first stage plus second stage).

[0082] Example 7

[0083] The difference between this embodiment and embodiment 1 is that in this embodiment, the second complexing agent solution is not added during the second stage coprecipitation reaction.

[0084] The rest of the preparation methods and parameters were the same as those in Example 1.

[0085] Example 8

[0086] The difference between this embodiment and embodiment 1 is that the concentration of the second complexing agent solution in this embodiment is 0.5 mol / L.

[0087] The rest of the preparation methods and parameters were the same as those in Example 1.

[0088] Comparative Example 1

[0089] This embodiment provides a lithium-rich manganese-based precursor material, the chemical formula of which is Ni 0.375 Mn 0.625 (OH)2.

[0090] The preparation method of the lithium-rich manganese-based precursor material is as follows:

[0091] Nickel sulfate and manganese sulfate were weighed according to the stoichiometric ratio of Ni:Mn=37.5:62.5 to prepare a 2 mol / L mixed salt solution; the mixed salt solution, 2 mol / L sodium hydroxide solution, and 0.1 mol / L ammonia solution were added to the bottom liquid of the reactor (water, sodium hydroxide, and ammonia solution were used as the bottom liquid, so that the pH value was 11.5-11.8, the concentration of ammonia solution was 0.3 mol / L, N2 was introduced, and the temperature was controlled at 40°C), and the mixture was stirred continuously at a speed of 400 r / min, and the pH of the reaction system was maintained at 10.0-10.5 for a coprecipitation reaction for 90 hours. After washing, drying, and sieving, Ni 0.375 Mn 0.625 (OH)2-like spherical lithium-rich manganese-based precursor material;

[0092] Nitrogen was introduced throughout the reaction.

[0093] The obtained precursor material was mixed with LiOH in a stoichiometric ratio of Me:Li=1:1.3, and then heated to 800℃, kept at this temperature for 10h, and then cooled in the furnace to obtain a spherical lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.3 Mn 0.5 O2.

[0094] Comparative Example 2

[0095] This embodiment provides an iron-doped lithium-rich manganese-based precursor material, wherein the iron-doped lithium-rich manganese-based precursor material comprises a lithium-rich manganese-based precursor matrix material and iron elements doped in the entire structure of the lithium-rich manganese-based precursor matrix material; the chemical formula of the lithium-rich manganese-based precursor matrix material is Ni 0.375 Mn 0.625 (OH)2.

[0096] The preparation method of the iron-doped lithium-rich manganese-based precursor material is as follows:

[0097] Nickel sulfate and manganese sulfate were weighed according to the stoichiometric ratio of Ni:Mn=37.5:62.5 to prepare a 2 mol / L mixed salt solution; the mixed salt solution was added into the bottom liquid of the reactor (water, sodium hydroxide and ammonia as the bottom liquid, the pH value of which was 11.5-11.8, the concentration of ammonia was 0.3 mol / L, N2 was introduced, and the temperature was controlled at 40°C) by coprecipitation reaction while stirring at a speed of 400 r / min and maintaining the pH of the reaction system at 10.0-10.5. After the reaction for 90 hours, the Ni-doped Fe-containing product was obtained after washing, drying and sieving. 0.375 Mn 0.625 (OH)2-like spherical lithium-rich manganese-based precursor material;

[0098] Nitrogen was introduced throughout the reaction.

[0099] The obtained precursor material was mixed with LiOH in a stoichiometric ratio of Me:Li=1:1.3, and then heated to 800℃, kept at this temperature for 10h, and then cooled in the furnace to obtain a spherical lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.3 Mn 0.5 O2, among which part of the Fe element forms a TMFe2O4 phase structure (TM is the main metal element) with the main metal element, which plays a protective role.

[0100] A lithium-ion battery was prepared using the positive electrode materials provided in Examples 1-8 and Comparative Examples 1-2:

[0101] A 7% polyvinylidene fluoride solution was prepared using N-methylpyrrolidone as a solvent. The positive electrode materials provided in Examples 1-8 and Comparative Examples 1-2, polyvinylidene fluoride, and conductive carbon black were mixed evenly in a mass ratio of 95:2:3. The mixture was then applied to an aluminum foil. The coated electrode was placed in a vacuum drying oven at 90°C and dried for 4 hours. The electrode was then rolled to a surface density of 4-7 mg / cm 2 For standby use, lithium metal sheet as counter electrode, 1 mol / LLiPF6 three-component mixed solvent with EC:DMC:EMC=1:1:1 (volume ratio) as electrolyte, and then assembled into 2032 button cells in an argon-filled glove box.

[0102] The lithium ion batteries provided in Examples 1-8 and Comparative Examples 1-2 were subjected to electrochemical performance tests under the following test conditions: 2.0-4.5 V, 0.2 C. The test results are shown in Table 1.

[0103] Table 1

[0104] From Table 1 we can conclude that:

[0105] From the data results of Example 1, Example 5 and Example 6, it can be seen that in the present application, the total reaction time in the coprecipitation reaction process is the sum of the reaction time of the coprecipitation reaction in the first stage and the reaction time of the coprecipitation reaction in the second stage; if the reaction time in the first stage accounts for too little, it will lead to excessive iron doping, which is not only distributed on the surface, thereby affecting the capacity; and if the reaction time in the first stage accounts for too much, it will lead to too little iron doping, which is not conducive to forming a good protective layer.

[0106] From the data results of Examples 1, 7 and 8, it can be seen that if the second complexing agent solution is not added at the same time as the iron source is added, it is difficult to achieve uniform distribution of Fe on the surface; and if the concentration of the added second complexing agent solution is too high, it is not conducive to the precipitation of Fe.

[0107] From the data results of Example 1 and Comparative Example 1, it can be seen that if the surface layer of the lithium-rich manganese-based precursor material is not doped with iron, the problem of cycle stability cannot be solved.

[0108] From the data results of Example 1 and Comparative Example 2, it can be seen that if iron is distributed throughout the entire structure of the lithium-rich manganese-based precursor material, the capacity is reduced and the cycle stability is slightly reduced.

[0109] To sum up, the preparation method provided by the present application is the preparation of a pure lithium-rich manganese-based precursor matrix material in the first stage. After the first stage, an iron source is further added on the basis of the original preparation to carry out the co-precipitation reaction in the second stage to achieve surface iron doping. At the same time, an iron-based lithium-rich manganese-based precursor material is obtained in the second stage, that is, iron is evenly distributed on the surface of the matrix material. The preparation method is simple, does not require a complicated preparation process, and is suitable for large-scale production. After further preparation of the positive electrode material, the iron element therein is converted into TMFe2O4 (TM is the main metal element), thereby improving the electrochemical properties of the lithium-rich manganese-based positive electrode material.

[0110] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of this application. It should be understood that the above is only a specific embodiment of this application and is not intended to limit this application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application should be included in the scope of protection of this application.

Claims

1. An iron-doped lithium-rich manganese-based precursor material, which comprises a lithium-rich manganese-based precursor matrix material and iron elements doped on the surface layer of the lithium-rich manganese-based precursor matrix material.

2. The iron-doped lithium-rich manganese-based precursor material according to claim 1, wherein, The chemical general formula of the lithium-rich manganese-based precursor matrix material is Mn x M y (OH)2, where M includes transition metal elements, 0 < x < 1, 0 < y < 1, and x + y = 1; Optionally, the M includes Ni and / or Co.

3. A preparation method of the iron-doped lithium-rich manganese-based precursor material according to claim 1 or 2, which comprises the following steps: Under a protective atmosphere, a main metal source mixed salt solution, a precipitant solution and a first complexing agent solution are added in parallel flow to carry out a first-stage co-precipitation reaction, then an iron source solution is added, and the second-stage co-precipitation reaction is continued to obtain the iron-doped lithium-rich manganese-based precursor material.

4. The preparation method of the iron-doped lithium-rich manganese-based precursor material according to claim 3, wherein, The concentration of the main metal source mixed salt solution is 2-4 mol / L; Optionally, in the main metal source mixed salt solution, the molar ratio of nickel, cobalt and manganese elements is (0.2-0.4):(0-0.1):(0.5-0.75); Optionally, the precipitant solution includes a sodium hydroxide solution; Optionally, the first complexing agent solution includes any one or a combination of at least two of an ammonia water solution, an oxalic acid solution or a sodium oxalate solution.

5. The preparation method of the iron-doped lithium-rich manganese-based precursor material according to claim 3 or 4, wherein, The temperature of the first-stage co-precipitation reaction is 25-80 °C; Optionally, the pH of the first-stage co-precipitation reaction is 10-12; Optionally, the rotation speed of the first-stage co-precipitation reaction is 200-400 r / min; Optionally, the reaction time of the first-stage co-precipitation reaction accounts for 88-91% of the total reaction time in the co-precipitation reaction process; Optionally, the reaction time of the first-stage co-precipitation reaction is 50-100 h. The temperature of the second-stage co-precipitation reaction is 25-80 °C; 6. The preparation method of the iron-doped lithium-rich manganese-based precursor material according to any one of claims 3-5, wherein, Optionally, the rotation speed of the second-stage co-precipitation reaction is 200-400 r / min; Optionally, the reaction time of the second-stage co-precipitation reaction is 5-15 h. When the iron source is added, a second complexing agent solution is also added; 7. The preparation method of the iron-doped lithium-rich manganese-based precursor material according to any one of claims 3-6, wherein, Optionally, the iron source solution includes a ferrous salt solution; Optionally, the concentration of the second complexing agent solution is 0.1-0.3 mol / L; Optionally, the second complexing agent solution includes any one or a combination of at least two of a citric acid solution, a sodium citrate solution, a lactic acid solution or a tartaric acid solution.

8. A preparation method of the iron-doped lithium-rich manganese-based precursor material according to any one of claims 3-7, which comprises the following steps: Under a protective atmosphere, a main metal source mixed salt solution, a precipitant solution and a first complexing agent solution are added in parallel flow to carry out a first-stage co-precipitation reaction, then an iron source solution and a second complexing agent solution with a concentration of 0.1-0.3 mol / L are added, and the second-stage co-precipitation reaction is continued to obtain the iron-doped lithium-rich manganese-based precursor material; ​ Among them, the first complexing agent solution includes any one or a combination of at least two of ammonia water solution, oxalic acid solution or sodium oxalate solution; the second complexing agent solution includes any one or a combination of at least two of citric acid solution, sodium citrate solution, lactic acid solution or tartaric acid solution; the reaction time of the coprecipitation reaction in the first stage accounts for 88-91% of the total reaction time in the coprecipitation reaction process.

9. An iron-doped lithium-rich manganese-based cathode material, wherein, The iron-doped lithium-rich manganese-based cathode material is obtained by mixing and sintering the precursor material as described in Claim 1 or 2 with a lithium source; the iron-doped lithium-rich manganese-based cathode material includes a lithium-rich manganese-based cathode matrix material and TMFe2O4 doped on the surface layer of the lithium-rich manganese-based cathode matrix material, wherein TM is the main metal element in the lithium-rich manganese-based cathode matrix material.

10. A lithium-ion battery, wherein, The lithium ion battery includes the iron-doped lithium-rich manganese-based cathode material as described in Claim 9.

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