Cobalt-free lithium-rich manganese-based positive electrode material based on bulk phase anion doping modification and preparation method of cobalt-free lithium-rich manganese-based positive electrode material

Abstract

The invention discloses a cobalt-free lithium-rich manganese-based positive electrode material based on bulk phase anion doping modification and a preparation method thereof, the chemical formula of the positive electrode material is 0.7 LiNi < 1-x > Mn < x > O < 2-0.3 > Li < 2 > Mn < O3 >, x is greater than 0 and less than 1, and the molar doping amount of PO4 < 3-> is 0.5-3%. The preparation method comprises the following steps: dissolving a nickel source, a lithium source, a manganese source and phosphate in deionized water to prepare a metal ion mixed solution, adding a dispersing agent, and uniformly stirring to obtain a dispersed solution; dissolving a complexing agent into deionized water to obtain a complexing agent solution; adding a complexing agent solution into the dispersion solution, and uniformly stirring to obtain a mixed solution; and carrying out spray drying and sintering to obtain the positive electrode material. The positive electrode material is a cobalt-free lithium-rich manganese-based positive electrode material which is doped with phosphate ions in a bulk phase or co-doped with the combination of the bulk phase and the body surface, so that the first coulombic efficiency of 0.1 C of the positive electrode material can reach about 80%, the capacity retention rate of 1C can reach 90% or above, and the positive electrode material has excellent electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of cobalt-free lithium-rich manganese-based cathode materials, and particularly relates to a cobalt-free lithium-rich manganese-based cathode material modified by bulk anion doping and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have the advantages of light weight, high energy density, stable cycling, and no memory effect, and are currently widely used in electric vehicles, portable electronic devices (such as laptop computers, mobile phones, digital cameras, etc.), and large-scale energy storage power stations. In lithium-ion batteries, the performance of the cathode material determines the performance and application scenarios of the lithium-ion battery. With the development of energy technology, there is a need for lithium-ion battery cathode materials with higher energy density to meet social needs. After lithium cobaltate and ternary lithium iron phosphate cathode materials, lithium-rich manganese-based cathode materials are considered to be the next generation of high-performance lithium-ion battery cathode materials. It has a discharge specific capacity of more than 250 mAh g -1 and an energy density of more than 1000 Wh kg -1 At the same time, by reducing the content of cobalt element with higher cost, the cost of the cathode material is further reduced.

[0003] Lithium-rich manganese-based cathode materials are formed by layered LiMO2 (M = Ni, Co, Mn) and Li2MnO3 in different proportions. So far, lithium-rich manganese-based cathode materials have been developed and promoted to industrialization by many well-known lithium-ion battery cathode material companies.

[0004] However, the large-scale commercial application of lithium-rich manganese-based cathode materials is still limited by many problems. For example, the loss of lattice oxygen results in a low initial Coulombic efficiency of lithium-rich manganese-based cathode materials; the low conductivity of the Li2MnO3 component and the high Mn reaction barrier limit the rate performance of the material; the limited two-dimensional diffusion path perpendicular to the (001) crystal plane leads to a decrease in ionic conductivity; side reactions occur between the electrolyte and the material surface, generating harmful substances, which further increases the material resistance, etc.

[0005] Therefore, in order to solve the above problems, it is of practical and profound significance to modify lithium-rich manganese-based cathode materials and promote their commercialization. Doping is one of the most common and effective modification methods. Classified by the type of doping element, doping is divided into anion doping and cation doping. According to the different doping positions of the doping element, it is divided into bulk and near-surface doping. The type of doping element and the doping position both have a great influence on the performance of the material.

[0006] Based on this, a cobalt-free lithium-rich manganese-based cathode material modified by anion doping is currently studied, that is, an anion bulk doping or a co-doping of bulk and near-surface is formed to improve the structural stability and electrochemical performance of the cathode material. Summary of the Invention

[0007] Objective of the Invention: The technical problem to be solved by the present invention is to provide a cobalt-free lithium-rich manganese-based cathode material with in-vivo anion doping and a preparation method thereof to improve its structural stability and electrochemical performance.

[0008] Technical Solution: The method for preparing a cobalt-free lithium-rich manganese-based cathode material modified by bulk anion doping according to the present invention is prepared by the following steps:

[0009] (1) Dissolve a nickel source, a lithium source, a manganese source and a phosphate in deionized water to obtain a mixed metal ion solution, and add a dispersant and stir evenly to obtain a dispersed solution; wherein, the molar doping amount of PO4 3- is 0.5-3%;

[0010] (2) Dissolve a complexing agent in deionized water to obtain a complexing agent solution;

[0011] (3) Add the complexing agent solution to the dispersed solution, stir evenly to obtain a mixed solution; then adjust the pH of the mixed solution to 8-10 with an alkali solution to obtain a suspension;

[0012] (4) Spray-dry the suspension at an inlet air temperature of 220-228 °C and an outlet air temperature of 80-120 °C to obtain a precursor; sinter the precursor at 250-350 °C for 2-4 h, 350-500 °C for 2-4 h and 800-950 °C for 8-14 h in sequence to obtain the cathode material.

[0013] In the present invention, by dissolving a nickel source, a lithium source, a manganese source and a phosphate in deionized water, and then adding a dispersant to fully disperse the metal ions to avoid aggregation, based on this condition, a complexing agent solution is added to complex the different uniformly dispersed metal ions, so as to realize the uniform dispersion of phosphate ions in the cathode material system. Subsequently, the pH value is adjusted to an alkaline condition to generate a complex precipitate with uniformly dispersed phosphate ions doped. Through the spray-drying and calcination processes, bulk doping can be formed on the cobalt-free lithium-rich manganese-based cathode material, thereby changing the local structure of the cathode material, appropriately increasing the unit cell parameter, and improving the cycle stability of the prepared cathode material. At the same time, with the increase of the doping amount, co-doping of the bulk and near-surface can be formed, further improving the electrochemical performance of the prepared cathode material.

[0014] In addition, based on the addition of the dispersant and the complexing agent, both of them can decompose to generate gases in the whole system through the spray-drying and calcination processes. The escape of the gases forms pores. On the basis of realizing doping, the specific surface area of the prepared cathode material is increased, and further the number of reactive sites is increased, further promoting the deintercalation reaction of lithium ions and improving the electrochemical performance.

[0015] Furthermore, in step (1) of the method for preparing the cobalt-free lithium-rich manganese-based cathode material of the present invention, the dispersant is polyethylene glycol, polyacrylamide or methyl pentanol, and the addition amount thereof is 2-5% of the mass of the metal ion mixed solution.

[0016] Furthermore, in step (1) of the method for preparing the cobalt-free lithium-rich manganese-based cathode material of the present invention, the nickel source is nickel sulfate, nickel nitrate, nickel acetate or nickel carbonate, and the manganese source is manganese sulfate, manganese nitrate, manganese acetate or manganese carbonate. The concentrations of both in the metal ion mixed solution are 0.5-2 mol / L.

[0017] Furthermore, in step (1) of the method for preparing the cobalt-free lithium-rich manganese-based cathode material of the present invention, the lithium salt is lithium acetate, lithium carbonate or lithium hydroxide.

[0018] Furthermore, in step (1) of the method for preparing the cobalt-free lithium-rich manganese-based cathode material of the present invention, the phosphate is ammonium dihydrogen phosphate, ammonium hydrogen phosphate or lithium dihydrogen phosphate, and the concentration of the phosphate in the metal ion mixed solution is 0.5-2 mol / L.

[0019] Furthermore, in step (2) of the method for preparing the cobalt-free lithium-rich manganese-based cathode material of the present invention, the concentration of the complexing agent solution is 0.5-2 mol / L, the complexing agent is citric acid, oxalic acid or lactic acid, and the molar mass ratio of the complexing agent to the total molar mass of nickel and manganese is (1.2-2):1.

[0020] The cobalt-free lithium-rich manganese-based cathode material prepared by the above preparation method of the present invention has the chemical formula 0.7LiNi 1-x Mn x O2·0.3Li2MnO3, 0 < x < 1. Preferably, 0.4 ≤ x ≤ 0.6.

[0021] Beneficial effects: Compared with the prior art, the remarkable advantages of the present invention are as follows: The preparation method realizes the doping of phosphate ions in the bulk phase of the cobalt-free lithium-rich manganese-based cathode material, or the co-doping of the bulk phase and the surface of the cathode material, improving the structural stability and electrochemical performance of the prepared cathode material. The first Coulombic efficiency at 0.1C can reach about 80%, and the capacity retention rate at 1C can reach more than 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the XRD pattern of the cathode material with a molar doping amount of 0.5% in Example 1 of the present invention;

[0023] Figure 2 It is the XRD pattern of the cathode material with a molar doping amount of 1% in Example 2 of the present invention;

[0024] Figure 3The 0.1C and 1C electrochemical curve graphs of the cathode material prepared in Example 2 of the present invention. Detailed implementation manners

[0025] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0026] Example 1

[0027] The chemical formula of the cobalt-free lithium-rich manganese-based cathode material prepared in this Example 1 is: 0.7LiNi 0.5 Mn 0.5 O2·0.3Li2MnO3, PO4 3- The molar doping amount is 0.5%. The preparation method of this cathode material includes the following steps:

[0028] (1) Weigh lithium acetate dihydrate, nickel acetate tetrahydrate, and manganese acetate tetrahydrate respectively according to the stoichiometric ratio Li:Ni:Mn = 1.3:0.35:0.65, and weigh ammonium dihydrogen phosphate according to the molar doping amount of 0.5%.

[0029] (2) Dissolve lithium acetate dihydrate, nickel acetate tetrahydrate, manganese acetate tetrahydrate, and ammonium dihydrogen phosphate in deionized water to prepare a metal ion mixed solution with a concentration of transition metal ions (nickel and manganese) of 1.5 mol / L, and add polyethylene glycol accounting for 3% of the mass of the metal ion mixed solution, and stir evenly to obtain a dispersion solution.

[0030] (3) Prepare a citric acid solution with a concentration of 1.5 mol / L, and the molar mass ratio of this citric acid to the total molar mass of nickel and manganese is 1.3:1.

[0031] (4) Pump the citric acid solution into the dispersion solution by a peristaltic pump, stir evenly to obtain a mixed solution; adjust the pH value to about 9 with 25% ammonia water to obtain a suspension; then obtain the precursor material by spray drying. The inlet air temperature of the spray drying is controlled at 225 °C, the outlet air temperature is controlled at 100 °C, and the feeding rate is 700 mL / h.

[0032] (5) Place the precursor in a muffle furnace in an air atmosphere, heat it to 300 °C at a heating rate of 5 °C / min and pre-burn for 3 h, then heat it to 500 °C at the same heating rate and calcine for 4 h, and then heat it to 850 °C at a heating rate of 3 °C / min and pre-burn for 12 h to obtain a cobalt-free lithium-rich manganese-based cathode material with anion bulk phase and near-surface co-doping.

[0033] Example 2

[0034] This Example 2 is basically the same as Example 1, the difference is that the molar doping amount of PO4 3- is 1%.

[0035] Example 3

[0036] This Example 3 is basically the same as Example 1, except that the molar doping amount of PO4 3- is 2%.

[0037] Example 4

[0038] This Example 4 is basically the same as Example 1, except that the molar doping amount of PO4 3- is 3%.

[0039] Comparative Example 1 - doping 4% of PO4 3-

[0040] This Comparative Example 1 is basically the same as Example 1, except that the molar doping amount of the doped PO4 3- is 4%.

[0041] Comparative Example 2 - without doping PO4 3-

[0042] The basic steps are basically the same as those of Example 1, except that PO4 is not doped 3- . The chemical formula of the cobalt-free lithium-rich manganese-based cathode material prepared in this Comparative Example 2 is: 0.7LiNi 0.5 Mn 0.5 O2·0.3Li2MnO3. The preparation method specifically includes the following steps:

[0043] (1) Weigh lithium acetate dihydrate, nickel acetate tetrahydrate, and manganese acetate tetrahydrate according to the stoichiometric ratio Li:Ni:Mn = 1.3:0.35:0.65 respectively.

[0044] (2) Dissolve lithium acetate dihydrate, nickel acetate tetrahydrate, and manganese acetate tetrahydrate in deionized water to prepare a metal ion mixed solution with a concentration of 1.5 mol / L of transition metal ions (nickel and manganese), and add 3% of polyethylene glycol based on the mass of the metal ion mixed solution, and stir evenly to obtain a dispersion solution.

[0045] (3) Prepare a citric acid solution with a concentration of 1.5 mol / L, and the molar mass ratio of this citric acid to the total molar mass of nickel and manganese is 1.3:1.

[0046] (4) Pump the citric acid solution into the dispersion solution by a peristaltic pump, and stir evenly to obtain a mixed solution; adjust the pH value to about 9 with 25% ammonia water; then obtain the precursor material through spray drying. The inlet air temperature of the spray drying is controlled at 225°C, the outlet air temperature is controlled at 100°C, and the feeding rate is 700 mL / h.

[0047] (5) Place the precursor in a muffle furnace under an air atmosphere, heat it to 300 °C at a heating rate of 5 °C / min and pre-calcine for 3 h, then heat it to 500 °C at the same heating rate and calcine for 4 h, and then heat it to 850 °C at a heating rate of 3 °C / min and pre-calcine for 12 h to obtain a cobalt-free lithium-rich manganese-based cathode material.

[0048] Structural characterization - bulk doping

[0049] Perform XRD characterization on the cathode materials prepared in Example 1 and Example 2, and the obtained results are as follows Figure 1 and Figure 2 as shown. By comparing Figure 1 and Figure 2 the XRD patterns, it can be seen that when the doping ratio is 0.5%, there are no impurity peaks in the XRD pattern, indicating that phosphate is doped into the crystal structure of the material, and this is bulk doping at this time; when the doping amount is 1%, the doping amount is small and the effect of coating the material cannot be achieved. At this time, in the XRD pattern of the material, impurity peaks of Li3PO4 appear, indicating that the phosphate at this time is doped into the bulk and the surface simultaneously.

[0050] Performance detection - electrochemical performance

[0051] Slurry the cathode materials prepared in the examples and comparative examples with polyvinylidene fluoride (PVDF) and acetylene black in a ratio of 8:1:1 to form an electrode sheet, and the compaction density of the electrode sheet is 2.0 g / cm 3 ,, use a lithium metal sheet as the negative electrode, use PE(2400) as the separator, use a 1 mol / L solution of lithium hexafluorophosphate in ethylene carbonate (EC) and dimethyl carbonate (DMC) (the mass ratio of EC to DMC is 2:1) as the electrolyte, assemble a button battery in a glove box filled with argon, and conduct electrochemical performance tests.

[0052] The conditions for the electrochemical performance test are: the charge-discharge voltage range is 2.0 V - 4.8 V, the test temperature is 25 °C, and the cycle performance of the battery is tested at a rate of 1 C starting from 3 cycles at 0.1 C. The obtained results are shown in Table 1 and Figure 1 as shown.

[0053] Table 1 Electrochemical performance test

[0054]

[0055]

[0056] Combined with Table 1 and Figure 3It can be seen that, compared with Comparative Example 2, the cathode materials prepared in Examples 1-4 of the present invention are doped and modified by a solution method, which can effectively improve the electrochemical performance of the prepared cathode materials. On the one hand, based on the solution method for doping and modification, under the action of a dispersant and a complexing agent, the doping can be evenly distributed, realizing the uniformity of distribution under trace doping; on the other hand, based on the use of the dispersant and the complexing agent in the solution method, voids are increased during calcination, thereby increasing the specific surface area of the prepared cathode material, increasing the reactive sites, and further improving the electrochemical performance. And by combining Comparative Example 1 and Example 2, it can be seen that the doping amount of phosphate ions is not the more the better, and excessive amount may form a surface coating, which will instead affect its electrochemical performance.

[0057] Comparative Example 3

[0058] The basic steps are the same as those in Example 1, except that no dispersant is added. The chemical formula of the cobalt-free lithium-rich manganese-based cathode material prepared in this Comparative Example 3 is: 0.7LiNi 0.5 Mn 0.5 O2·0.3Li2MnO3, PO4 3- The molar doping amount is 0.5%. The preparation method of this cathode material includes the following steps:

[0059] (1) Weigh lithium acetate dihydrate, nickel acetate tetrahydrate, and manganese acetate tetrahydrate according to the stoichiometric ratio Li:Ni:Mn = 1.3:0.35:0.65 respectively, and weigh ammonium dihydrogen phosphate according to the molar doping amount of 0.5%.

[0060] (2) Dissolve lithium acetate dihydrate, nickel acetate tetrahydrate, manganese acetate tetrahydrate, and ammonium dihydrogen phosphate in deionized water to prepare a metal ion mixed solution with a concentration of transition metal ions (nickel and manganese) of 1.5 mol / L.

[0061] (3) Prepare a citric acid solution with a concentration of 1.5 mol / L, and the molar mass ratio of this citric acid to the total molar mass of nickel and manganese is 1.3:1.

[0062] (4) Pump the citric acid solution into the metal ion mixed solution by a peristaltic pump, stir evenly to obtain a mixed solution; adjust the pH value to about 9 with 25% ammonia water; then obtain the precursor material by spray drying. The inlet air temperature of the spray drying is controlled at 225 °C, the outlet air temperature is controlled at 100 °C, and the feeding rate is 700 mL / h.

[0063] (5) Place the precursor in a muffle furnace under an air atmosphere, heat it to 300 °C at a heating rate of 5 °C / min for pre-calcination for 3 h, then heat it to 500 °C at the same heating rate for calcination for 4 h, and then heat it to 850 °C at a heating rate of 3 °C / min for pre-calcination for 12 h to obtain a cobalt-free lithium-rich manganese-based cathode material with anion bulk and near-surface co-doping.

[0064] Performance testing - Electrochemical performance

[0065] Perform electrochemical performance testing on the cathode material prepared in Comparative Example 3, and the obtained results are shown in Table 2 below.

[0066] Table 2 Electrochemical performance test

[0067]

[0068] Combined with Table 2, it can be seen that in the preparation of the present invention, by not introducing a dispersant, compared with not doping phosphate ions, its electrochemical performance is rather poor, thus verifying the importance of the uniform distribution of trace-doped phosphate ions in the cathode material system. And the addition of the dispersant can also generate gas and escape during the subsequent calcination process, further increasing the specific surface area of the prepared cathode material, increasing the surface active sites, and improving the electrochemical performance.

[0069] In addition to the above embodiments, it should be noted that by adopting the process steps and process parameters defined in the present invention, that is, based on Example 1, expanding adjacent values, the technical effects of improving the electrochemical performance and structural stability claimed above can be achieved from the technical mechanism. Therefore, no further experimental verification will be carried out one by one in the specific implementation part. And the cobalt-free lithium-rich manganese-based cathode material of the present invention can be prepared into a cathode material with a corresponding chemical formula according to the molar ratio of different metal ions. The only difference is the difference in the content of different metal ions, which will affect the electrochemical performance, but as long as 0.5 - 3% of PO4 is ensured to be incorporated 3- All can improve the electrochemical performance compared with non-doping.

Claims

1. A method for preparing a cobalt-free lithium-rich manganese-based cathode material modified by bulk anion doping, characterized in that, It includes the following steps: (1) Dissolve a nickel source, a lithium source, a manganese source, and a phosphate in deionized water to prepare a mixed metal ion solution, and add a dispersant and stir evenly to obtain a dispersion solution; wherein, the molar doping amount of PO4 3- is 0.5-3%; (2) Dissolve the complexing agent in deionized water to obtain a complexing agent solution; (3) Add the complexing agent solution to the dispersion solution and stir evenly to obtain a mixed solution; then adjust the pH of the mixed solution to 8 - 10 with an alkali solution to obtain a suspension; (4) Spray-dry the suspension at an inlet air temperature of 220 - 228 °C and an outlet air temperature of 80 - 120 °C to obtain a precursor; sinter the precursor at 250 - 350 °C for 2 - 4 h, 350 - 500 °C for 2 - 4 h, and 800 - 950 °C for 8 - 14 h in sequence to obtain the cathode material.

2. The method for preparing the cobalt-free lithium-rich manganese-based cathode material modified by bulk anion doping according to claim 1, wherein, In step (1), the dispersant is polyethylene glycol, polyacrylamide or methyl pentanol, and its addition amount is 2 - 5% of the mass of the metal ion mixed solution.

3. The method for preparing a cobalt-free lithium-rich manganese-based cathode material modified by bulk anion doping according to claim 1, characterized in that, In step (1), the nickel source is nickel sulfate, nickel nitrate, nickel acetate or nickel carbonate, the manganese source is manganese sulfate, manganese nitrate, manganese acetate or manganese carbonate, and their concentrations in the metal ion mixed solution are 0.5 - 2 mol / L.

4. The method for preparing the cobalt-free lithium-rich manganese-based cathode material modified by bulk anion doping according to claim 1, wherein In step (1), the lithium salt is lithium acetate, lithium carbonate or lithium hydroxide.

5. The method for preparing a cobalt-free lithium-rich manganese-based cathode material modified by bulk anion doping according to claim 1, characterized in that, In step (1), the phosphate is ammonium dihydrogen phosphate, ammonium hydrogen phosphate or lithium dihydrogen phosphate.

6. The method for preparing a cobalt-free lithium-rich manganese-based cathode material modified by bulk anion doping according to claim 1, wherein In step (2), the concentration of the complexing agent solution is 0.5 - 2 mol / L, the complexing agent is citric acid, oxalic acid or lactic acid, and the molar mass ratio of the complexing agent to the total molar mass of nickel and manganese is (1.2 - 2):

1.

7. The cobalt-free lithium-rich manganese-based cathode material prepared by the preparation method according to claim 1, characterized in that, The chemical formula of this cobalt-free lithium-rich manganese-based cathode material is 0.7LiNi 1-x Mn x O2·0.3Li2MnO3, where 0 < x < 1.

8. The cobalt-free lithium-rich manganese-based cathode material according to claim 7, characterized in that, The value of x is 0.4 ≤ x ≤ 0.6.

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