Preparation method of modified positive electrode material

Abstract

The present disclosure relates to a preparation method of a modified positive electrode material, comprising: mixing a raw material for preparing the positive electrode material with a modifier, and preparing the modified positive electrode material by using a solid phase method, wherein: the modifier comprises a transition metal carbide, and the positive electrode material is lithium iron phosphate or lithium iron manganese phosphate. The present disclosure modifies lithium iron manganese phosphate and lithium iron phosphate positive electrode materials by using a transition metal carbide as a doping precursor modifier, which can effectively improve the electrical conductivity of the positive electrode material, improve the electrochemical performance of the positive electrode material, and can also be used as a reducing agent without additional addition of a carbon source, and is environmentally friendly and low in cost.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of lithium ion battery cathode material, and particularly relates to a preparation method of modified cathode material. BACKGROUND

[0002] LiMPO4 (M=Fe, Mn, Co, Ni, etc.) with olivine structure is a promising cathode material for lithium ion batteries, but their electrical conductivity and capacity are both low. For example, lithium iron phosphate LiFePO4 (LFP) has lower cost, better safety performance, lower toxicity and extremely flat charge-discharge platform compared with traditional cathodes, and has a reasonable high potential of 3.4 V compared with Li / Li + However, its theoretical capacity is only 175 mAh / g, and its inherent electronic conductivity is poor, and the tap density is small. Recently, LiFe x Mn 1-x PO4 (LMFP) which combines the advantages of LiFePO4 and LiMnPO4 has been widely studied. However, the low electrical conductivity of lithium iron manganese phosphate is still a major problem in practical applications.

[0003] Elemental doping is an important means to improve the intrinsic electrical conductivity of the cathode material. Doping usually has two types, cation doping and anion doping. Among them, cation doping includes transition metal M (Mn and Fe) site substitution and lithium site substitution, and the principle is that when the doping ions occupy the Fe, Li or Mn sites, the lattice spacing is expanded, the Li vacancies are increased, and the Li + transfer channel is expanded to improve the electrical conductivity. In the doping process, the commonly used ones reported are metal oxides, oxalates, acetates, etc. In addition, in the preparation process of lithium iron manganese phosphate and lithium iron phosphate cathode material, in order to prevent Fe 2+ from being oxidized to Fe 3+ , a carbon source or other reducing agent needs to be added.

[0004] Therefore, it is particularly important to provide a modifier which contains the required doping metal elements and can also play a reducing role for the modification of the cathode material. SUMMARY

[0005] In order to solve the above technical problems, the present disclosure provides a preparation method of modified cathode material.

[0006] In a first aspect, the present disclosure provides a preparation method of modified cathode material, the preparation method comprising: mixing a raw material for preparing the cathode material with a modifier, and preparing the modified cathode material by using a solid phase method, wherein:

[0007] The modifier comprises a transition metal carbide, and the cathode material is lithium iron phosphate or lithium iron manganese phosphate.

[0008] The present disclosure modifies lithium manganese iron phosphate and lithium iron phosphate cathode materials by using transition metal carbide as a doping precursor modifier, which can effectively improve the electrical conductivity of the cathode material, improve the electrochemical performance of the cathode material, and also can be used as a reducing agent, without additional addition of carbon source, environmentally friendly and low cost. Specifically:

[0009] In the preparation method of the present disclosure, the transition metal carbide contains the required doping metal elements, which can improve the electrical conductivity and ion diffusion rate of the cathode material, effectively improve the electrochemical performance of the cathode material, and at the same time, the carbon contained in the transition metal carbide can also be used as a reducing agent in the preparation process to prevent Fe 2+ oxidation to Fe 3+ , without additional addition of carbon source, environmentally friendly and low cost, and the carbon can also be attached to the surface of the cathode material to improve the electrical conductivity of the cathode material, while increasing the specific surface area of the cathode material to reduce the diffusion distance of lithium ions and accelerate the electrochemical reaction speed.

[0010] As a preferred technical solution of the present disclosure, the modified cathode material is LiFe x Mn y M 1-x-y PO4;

[0011] Wherein, M is a transition metal, 0.001≤x≤0.999, x can be 0.005, 0.01, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 0.9, etc.; 0≤y≤0.999, y can be 0.005, 0.01, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 0.9, etc., when y is 0, the modified cathode material is a transition metal carbide doped lithium iron phosphate.

[0012] As a preferred technical solution of the present disclosure, 0.5≤x≤0.999, x can be 0.6, 0.7, 0.8, 0.9, etc.

[0013] As a preferred technical solution of the present disclosure, 0.008≤1-x-y≤0.012, 1-x-y can be 0.009, 0.01, 0.011, etc.

[0014] As a preferred technical solution of the present disclosure, the transition metal carbide is selected from any one or a combination of at least two of Mo2C, NbC, TiC, WC or PbC.

[0015] There is no report on the use of transition metal carbide as a doping precursor in the current lithium manganese iron phosphate or lithium iron phosphate doping work, and the present disclosure fills this gap by using transition metal carbide as a doping precursor to modify the preparation method of lithium manganese iron phosphate and lithium iron phosphate cathode materials.

[0016] As a preferred technical solution of the present disclosure, when the positive electrode material is lithium iron phosphate, the preparation raw material of the positive electrode material comprises an iron source, a phosphorus source and a lithium source; when the positive electrode material is lithium iron manganese phosphate, the preparation raw material of the positive electrode material comprises an iron source, a manganese source, a phosphorus source and a lithium source.

[0017] As a preferred technical solution of the present disclosure, the preparation raw material of the positive electrode material further comprises a carbon source.

[0018] In the preparation method of the present disclosure, the modified positive electrode material can be obtained by reaction without additional carbon source, and the carbon source can not only prevent Fe 2+ from being oxidized to Fe 3+ , but also can be attached to the surface of the positive electrode material to form a carbon layer, further improving the electrical conductivity of the positive electrode material, increasing the specific surface area of the positive electrode material, reducing the diffusion distance of lithium ions and accelerating the electrochemical reaction speed.

[0019] As a preferred technical solution of the present disclosure, the molar ratio of Fe:Mn:P:Li:M in the iron source, the optional manganese source, the phosphorus source, the lithium source and the metal carbide is x:y:1:1:1-x-y.

[0020] As a preferred technical solution of the present disclosure, the mass ratio of the lithium source to the carbon source is (50-60):1, for example, 52:1, 54:1, 56:1, 58:1, etc., and preferably 58.3:1.

[0021] As a preferred technical solution of the present disclosure, the iron source is selected from any one or a combination of at least two of ferrous oxide, ferrous oxalate, ferrous acetate, ferrous sulfate, ferrous chloride, ferric nitrate or ferrous phosphate.

[0022] As a preferred technical solution of the present disclosure, the iron source is selected from ferrous oxalate and / or ferrous oxide.

[0023] As a preferred technical solution of the present disclosure, the manganese source is selected from any one or a combination of at least two of manganese carbonate, manganese acetate, manganese sulfate or manganese chloride.

[0024] As a preferred technical solution of the present disclosure, the phosphorus source is selected from any one or a combination of at least two of ammonium dihydrogen phosphate, diammonium hydrogen phosphate or phosphoric acid.

[0025] As a preferred technical solution of the present disclosure, the lithium source is selected from any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium acetate or lithium dihydrogen phosphate.

[0026] As a preferred technical solution of the present disclosure, the carbon source is selected from any one or a combination of at least two of sucrose, glucose, citric acid or polyethylene glycol.

[0027] As a preferred technical solution of the present disclosure, the solid phase method is carried out in an inert atmosphere, the reaction temperature of the solid phase method is 600-800 DEG C, and the reaction time is 10-24 h.

[0028] As a specific embodiment of the present disclosure, the preparation method of the modified positive electrode material comprises: uniformly mixing the iron source, the optional manganese source, the phosphorus source, the lithium source, the optional carbon source and the metal carbide in proportion, and then annealing under the conditions of an inert atmosphere, 600-800 DEG C for 10-24 h to obtain the metal carbide modified lithium manganese iron phosphate or the metal carbide modified lithium iron phosphate LiFe x Mn y M 1-x-y PO4.

[0029] In a second aspect, the present disclosure provides a modified positive electrode material prepared by the preparation method of the first aspect, wherein the modified positive electrode material is a transition metal carbide doped lithium iron phosphate or a transition metal carbide doped lithium manganese iron phosphate, and has excellent electrochemical performance.

[0030] In a third aspect, the present disclosure provides a positive electrode sheet comprising the modified positive electrode material of the second aspect.

[0031] In a fourth aspect, the present disclosure provides an electrochemical device comprising the modified positive electrode material of the second aspect or the positive electrode sheet of the third aspect.

[0032] The technical solution provided by the embodiments of the present disclosure has the following advantages compared with the prior art:

[0033] The present disclosure modifies the lithium manganese iron phosphate and lithium iron phosphate positive electrode material by using the transition metal carbide as a doping precursor modifier, which can effectively improve the electrical conductivity of the positive electrode material, improve the electrochemical performance of the positive electrode material, and can also be used as a reducing agent without additional carbon source, which is environmentally friendly and low in cost. BRIEF DESCRIPTION OF DRAWINGS

[0034] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present disclosure and, together with the specification, serve to explain the principles of the present disclosure.

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0036] Figure 1A CV curve diagram of the modified positive electrode material prepared for Embodiment 6 of the present disclosure;

[0037] Figure 2 A rate performance diagram of the modified positive electrode material prepared for Embodiment 7 of the present disclosure. DETAILED DESCRIPTION

[0038] In order to enable a more clear understanding of the above-mentioned purposes, features and advantages of the present disclosure, the schemes of the present disclosure will be further described below. It should be noted that the embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0039] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present disclosure, but the present disclosure can also be implemented in other manners different from those described herein; obviously, the embodiments described in the specification only constitute a part of the embodiments of the present disclosure, and not all the embodiments.

[0040] Embodiment 1

[0041] The present embodiment provides a LiFe 0.99 Mo 0.01 PO4modified positive electrode material and a preparation method thereof, and the preparation method is as follows:

[0042] 2.16 g of FeC2O4·2H2O (12 mmol), 0.0123 g of Mo2C (0.06 mmol), 2.3 g of NH4H2PO4(20 mmol) and 0.73 g of Li2CO3(10 mmol) are weighed and mixed and ball-milled for 1 h. The molar ratio of Li:Fe:Mo:P is 1:0.99:0.01:1, and then annealed at 700°C for 10 h under argon in a tube furnace to obtain the modified positive electrode material.

[0043] Embodiment 2

[0044] The present embodiment provides a LiFe 0.6 Mo 0.01 Mn 0.39 PO4modified positive electrode material and a preparation method thereof, and the preparation method is as follows:

[0045] Take 2.16 g FeC2O4·2H2O (12 mmol), 0.92 g MnCO3 (7.8 mmol), 0.0203 g Mo2C (0.1 mmol), 2.3 g NH4H2PO4 (20 mmol) and 0.73 g Li2CO3 (10 mmol), and mix ball mill for 1 h. The molar ratio of Li:Fe:Mo:Mn:P is 1:0.6:0.01:0.39:1, and then annealed at 700 ℃ for 10 h in a tube furnace under argon atmosphere to obtain the modified cathode material.

[0046] Example 3-4

[0047] The embodiment provides a modified cathode material and a preparation method thereof, and the difference from the embodiment 2 is that the molar ratio of Fe:Mo:Mn is controlled, so that the modified cathode material is LiFe 0.9 Mo 0.008 Mn 0.092 PO4 (Example 3) and LiFe 0.1 Mo 0.012 Mn 0.888 PO4 (Example 4).

[0048] Example 5

[0049] The embodiment provides a modified cathode material and a preparation method thereof, and the difference from the embodiment 2 is that the modified cathode material is LiFe 0.6 Nb 0.01 Mn 0.39 PO4, the transition metal carbide is NbC, the iron source is diiron trioxide, the manganese source is manganese chloride, the phosphorus source is diammonium hydrogen phosphate, and the lithium source is lithium dihydrogen phosphate.

[0050] Example 6

[0051] The embodiment provides a modified cathode material and a preparation method thereof, and the difference from the embodiment 2 is that 0.471 g of sucrose is further added in the preparation raw material.

[0052] Example 7

[0053] The embodiment provides a modified cathode material and a preparation method thereof, and the difference from the embodiment 2 is that the annealing time is 24 h.

[0054] Example 8

[0055] The embodiment provides a modified cathode material and a preparation method thereof, and the difference from the embodiment 2 is that the annealing temperature is 650 ℃, and the annealing time is 24 h.

[0056] Example 9

[0057] The embodiment provides a modified positive electrode material and a preparation method thereof, and the difference from the embodiment 2 is that the iron source is diiron trioxide, the annealing temperature is 650 DEG C, and the annealing time is 24 h.

[0058] Comparative example 1

[0059] The comparative example provides a positive electrode material and a preparation method thereof, and the difference from the embodiment 2 is that Mo2C is not added.

[0060] Comparative example 2

[0061] The comparative example provides a modified positive electrode material and a preparation method thereof, and the difference from the embodiment 2 is that Mo2C is replaced by MoO.

[0062] Comparative example 3

[0063] The comparative example provides a positive electrode material and a preparation method thereof, and the difference from the embodiment 2 is that Mo2C is replaced by 0.471 g sucrose.

[0064] Comparative example 4

[0065] The comparative example provides a modified positive electrode material and a preparation method thereof, and the difference from the embodiment 2 is that Mo2C is replaced by MoO, and 0.471 g sucrose is additionally added in the preparation raw material.

[0066] Performance test 1

[0067] The positive electrode materials obtained from the embodiment 1-9 and the comparative examples 1-4 are subjected to electrical conductivity test. The test method is four-probe method, and the results are shown in Table 1:

[0068] Table 1

[0069]

[0070] It is known from the embodiment 1-9 that the preparation method provided by the present disclosure uses the transition metal carbide as the modifier, which can effectively improve the electrical conductivity of the positive electrode material and improve the electrochemical performance of the positive electrode material. It is known from the comparison between the embodiment 2 and the comparative examples 1-3 that when the transition metal carbide is not added and the carbon source is not additionally added (comparative example 1), or the transition metal element is added but the carbon source is not added (comparative example 2), or the carbon source is added but the transition metal element is not added (comparative example 3), the electrical conductivity of the positive electrode material prepared is low, and it is known from the comparison between the embodiment 2 and the comparative example 4 that the addition of the transition metal carbide and the separate addition of the transition metal element and the carbon source have the same effect, which indicates that the transition metal carbide of the present disclosure simultaneously plays the roles of improving the electrical conductivity of the positive electrode material and the reducing agent.

[0071] Performance test 2

[0072] The modified positive electrode material prepared in Example 6 was tested by cyclic voltammetry, and a CV curve diagram thereof was obtained, as shown in Figure 1 From the diagram, it can be seen that the peak current in the CV curve is high, that is, the prepared modified positive electrode material has excellent kinetic performance.

[0073] Performance test 3

[0074] The positive electrode materials obtained in Examples 1-9 and Comparative Examples 1-4 were subjected to constant current charge-discharge test, and the results are shown in Table 2, wherein the rate performance diagram of the positive electrode material obtained in Example 2 is shown in Figure 2 .

[0075] Table 2

[0076]

[0077] From Table 2 or Figure 2 , it can be seen that the rate performance of the positive electrode material after doping Mo is improved.

[0078] It should be noted that, in this document, relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0079] The above description is merely one specific implementation of the disclosure, and those skilled in the art can understand or implement the disclosure based on the above description. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the disclosure. Therefore, the disclosure will not be limited to these embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a modified cathode material, characterized in that, The preparation method includes: mixing the raw materials for preparing the cathode material with a modifier, and preparing the modified cathode material using a solid-state method, wherein: The modifier includes transition metal carbides, and the cathode material is lithium iron phosphate or lithium iron manganese phosphate. The modified cathode material is LiFe. x Mn y M 1-x-y PO4; Where M is a transition metal, 0.001≤x≤0.999, 0≤y≤0.999; The transition metal carbide is selected from any one or a combination of at least two of Mo2C, NbC, TiC or WC; The solid-phase method is carried out in an inert atmosphere, and the reaction temperature is 600-800℃, with a reaction time of 10-24 h.

2. The preparation method according to claim 1, characterized in that, 0.5≤x≤0.999。 3. The preparation method according to claim 1 or 2, characterized in that, 0.008≤1-xy≤0.

012.

4. The preparation method according to claim 1, characterized in that, When the cathode material is lithium iron phosphate, the raw materials for preparing the cathode material include an iron source, a phosphorus source, and a lithium source; when the cathode material is lithium iron manganese phosphate, the raw materials for preparing the cathode material include an iron source, a manganese source, a phosphorus source, and a lithium source.

5. The preparation method according to claim 4, characterized in that, The raw materials for preparing the cathode material also include a carbon source.

6. The preparation method according to claim 5, characterized in that, The mass ratio of the lithium source to the carbon source is 50-60:

1.

7. The preparation method according to claim 5, characterized in that, The iron source is selected from any one or a combination of at least two of ferric oxide, ferrous oxalate, ferrous acetate, ferrous sulfate, ferrous chloride, ferrous nitrate, or ferrous phosphate. And / or, the manganese source is selected from any one or a combination of at least two of manganese carbonate, manganese acetate, manganese sulfate or manganese chloride; And / or, the phosphorus source is selected from any one or a combination of at least two of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or phosphoric acid; And / or, the lithium source is selected from any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium acetate or lithium dihydrogen phosphate; And / or, the carbon source is selected from any one or a combination of at least two of sucrose, glucose, citric acid or polyethylene glycol.

8. The preparation method according to claim 7, characterized in that, The iron source is selected from ferrous oxalate and / or ferric oxide.

9. The modified cathode material prepared by the preparation method according to any one of claims 1-8.

10. A positive electrode plate, characterized in that, The positive electrode sheet comprises the modified positive electrode material as described in claim 9.

11. An electrochemical device, characterized in that, The electrochemical device includes the modified cathode material of claim 9 or the cathode sheet of claim 10.

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