Modified lithium ferric manganese phosphate positive electrode material as well as preparation method and application thereof

Abstract

The invention discloses a modified lithium ferric manganese phosphate positive electrode material as well as a preparation method and application thereof. The modified lithium ferric manganese phosphate positive electrode material is a mixture composed of a composite material composed of lithium ferric manganese phosphate and carbon and a modifier MFeAsOxF (1-x), wherein M is one of La, Nd, Ce and Pr, and x is more than or equal to 0.8 and less than or equal to 0.9. According to the invention, a composite material composed of carbon and lithium ferric manganese phosphate is mixed with a modifier MFeAsOxF (1-x), such that the modified lithium ferric manganese phosphate positive electrode material is obtained. Carbon and lithium ferric manganese phosphate are subjected to composite modification, so that the conductivity of lithium ferric manganese phosphate can be improved, the conductivity is further enhanced after the carbon and lithium ferric manganese phosphate are mixed with the modifier MFeAsOxF1-x, and the carbon and the modifier MFeAsOxF1-x have a synergistic effect, so that the transmission efficiency of electrons and ions of the lithium ferric manganese phosphate material can be synchronously improved, the energy consumption is reduced, and the service life of the lithium ferric manganese phosphate material is prolonged. And the capacity reversibility and the capacity retention ratio of the lithium ferric manganese phosphate material are effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a modified lithium iron manganese phosphate cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium iron manganese phosphate has the characteristics of high stability and low production cost, and has become one of the candidate cathode materials for current lithium-ion batteries; however, its crystal structure contains PO4 tetrahedrons, which greatly limits the movement space of lithium ions and directly affects the electron and ion diffusion rates of lithium iron manganese phosphate. In order to improve the performance of lithium iron manganese phosphate, the current main modification schemes include carbon coating, ion doping, nanosizing, designing specific morphologies, etc., but these modification schemes have limited improvement in the electrochemical performance of the lithium iron manganese phosphate cathode material, especially the electrochemical performance at low temperatures. Summary of the Invention

[0003] Aiming at the above problems, the purpose of the present invention is to provide a modified lithium iron manganese phosphate cathode material with good electrochemical performance, a preparation method thereof, and an application thereof.

[0004] In the first aspect, the present invention provides a modified lithium iron manganese phosphate cathode material, which is a mixture composed of a composite material of lithium iron manganese phosphate and carbon and a modifier MFeAsO x F 1-x ; wherein: M is one of La, Nd, Ce, and Pr, and 0.8 ≤ x ≤ 0.9.

[0005] Preferably, the chemical formula of the composite material composed of lithium iron manganese phosphate and carbon is LiMn y Fe 1-y PO4 / C, wherein: 0.1 ≤ y ≤ 0.6.

[0006] Preferably, the mass ratio of the composite material composed of lithium iron manganese phosphate and carbon to the modifier MFeAsO x F 1-x is 1:(0.03 - 0.08).

[0007] In the second aspect, the present invention provides a preparation method of a modified lithium iron manganese phosphate cathode material, including the following steps: Solid-phase mixing of the composite material composed of lithium iron manganese phosphate and carbon and the modifier MFeAsO x F 1-x to obtain the modified lithium iron manganese phosphate cathode material.

[0008] Preferably, the preparation method of the composite material composed of lithium iron manganese phosphate and carbon includes the following steps: Disperse a manganese source, an iron source, a lithium source, and a carbon source in water to form a metal salt solution, and dissolve a phosphate in water to form a phosphate solution; add the phosphate solution to the metal salt solution, and after heating and reacting, obtain a lithium iron manganese phosphate precursor material; sinter the lithium iron manganese phosphate precursor material in an inert atmosphere to obtain a composite material composed of lithium iron manganese phosphate and carbon.

[0009] Further preferably, the manganese source is one or both of manganese acetate and manganese nitrate; the iron source is one or both of ferrous acetate and ferrous nitrate; the lithium source is one or both of lithium nitrate and lithium acetate; the carbon source is one or more of glucose, starch, and polyvinylpyrrolidone (PVP); the phosphate is one or both of diammonium hydrogen phosphate and ammonium dihydrogen phosphate.

[0010] Further preferably, the molar ratio of Li, Mn, Fe, and PO4 in the lithium source, manganese source, iron source, and phosphate is (1.01~1.04):y:(1 - y):1, where 0.1 ≤ y ≤ 0.6; the mass ratio of the lithium source to the carbon source is 1:(0.01~0.03). 3-

[0011] Further preferably, the temperature of the heating reaction is 60~90 °C, and the time of the heating reaction is 10~24 h.

[0012] Further preferably, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere; the sintering temperature is 800~1000 °C, and the sintering time is 10~30 h.

[0013] Preferably, the preparation method of the modifier MFeAsO x F 1-x comprises the following steps: After ball-milling and mixing raw materials MAs, FeAs, Fe, MF3, and Fe2O3, obtain a mixed powder, and sinter the mixed powder in an oxygen-containing atmosphere to obtain the modifier MFeAsO x F 1-x .

[0014] Further preferably, MAs, FeAs, Fe, MF3, and Fe2O3 are added according to the stoichiometric ratio of the chemical formula of the modifier MFeAsO x F 1-x .

[0015] Further preferably, the oxygen-containing atmosphere is an oxygen atmosphere or an air atmosphere, the sintering temperature is 850~1000 °C, and the sintering time is 10~30 h.

[0016] ​Preferably, the solid-phase mixing is ball-milling mixing, the ball-milling speed is 300-500 rpm, and the ball-milling time is 0.5-2 h.

[0017] In a third aspect, the present invention provides a lithium-ion battery, including the aforementioned modified lithium iron manganese phosphate cathode material.

[0018] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: (1) In the present invention, the composite material composed of carbon and lithium iron manganese phosphate is further mixed with the modifier MFeAsO x F 1-x First, the combination of carbon and lithium iron manganese phosphate can improve the conductivity of lithium iron manganese phosphate. After it is further mixed with the modifier MFeAsO x F 1-x the conductivity will be further enhanced. Moreover, carbon and the modifier MFeAsO x F 1-x have a synergistic effect, which can synchronously improve the electron and ion transport efficiency of the lithium iron manganese phosphate material, reduce energy consumption, and thus effectively improve the capacity reversibility and capacity retention rate of the lithium iron manganese phosphate material. In addition, the presence of carbon can inhibit the formation of trivalent iron in lithium iron manganese phosphate, ensuring the purity and structural stability of lithium iron manganese phosphate.

[0019] (2) The modifier MFeAsO x F 1-x in the present invention has superconductivity, which can effectively improve the conductivity of the cathode material and promote the transport of lithium ions. Moreover, it can still have good conductivity at low temperatures for lithium iron manganese phosphate, and thus effectively improve the structural stability and electrochemical stability of the cathode material at low temperatures. In addition, the modifier MFeAsO x F 1-x can improve the structural stability of lithium iron manganese phosphate, enabling the cathode material to maintain good structural integrity during the electrochemical reaction process, thereby effectively enhancing the long-cycle stability of the cathode material.

[0020] (3) The preparation method in the present invention is simple, easy to operate, and easy to realize large-scale industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a cycle performance graph of the batteries assembled with the modified lithium iron manganese phosphate cathode materials prepared in Examples 1-5 and Comparative Examples 1-3.

[0022] Figure 2 It is a cycle performance graph of the batteries assembled with the modified lithium iron manganese phosphate cathode materials prepared in Example 1 and Comparative Example 1 at 0°C. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] To facilitate the understanding of the present invention, the present invention will be described more comprehensively and in detail below in conjunction with the accompanying drawings of the specification and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0024] Example 1 In this example, a modified lithium iron manganese phosphate cathode material is prepared, including a composite material composed of lithium iron manganese phosphate and carbon (LiMn 0.5 Fe 0.5 PO4 / C) and a modifier LaFeAsO 0.88 F 0.12 . The specific preparation method is as follows: (1) 0.2 mol of manganese acetate, 0.2 mol of ferrous acetate, 0.408 mol (26.9 g) of lithium acetate, and 0.538 g of PVP are dispersed in 400 ml of deionized water to form a metal salt solution. Separately, 0.4 mol of (NH4)2HPO4 is dissolved in 200 ml of deionized water to form a phosphate solution. Under stirring conditions, the phosphate solution is added to the metal salt solution, and then heated at 70 °C for 16 h to fully react to obtain a lithium iron manganese phosphate precursor. After the lithium iron manganese phosphate precursor is dried at 100 °C for 20 h, a dry gel-like lithium iron manganese phosphate precursor material is obtained. After the dry gel-like lithium iron manganese phosphate precursor material is ball-milled and pulverized, it is sintered at 900 °C for 22 h in a nitrogen atmosphere to obtain a composite material composed of lithium iron manganese phosphate and carbon (LiMn 0.5 Fe 0.5 PO4 / C).

[0025] (2) 0.072 mol of LaAs, 0.003 mol of FeAs, 0.028 mol of Fe, 0.003 mol of LaF3, and 0.022 mol of Fe2O3 materials are weighed in proportion, and after ball-milling and solid-phase mixing, a mixed powder is obtained. The mixed powder is transferred into a magnetic boat and sintered at 950 °C for 18 h in an oxygen atmosphere to obtain the modifier LaFeAsO 0.88 F 0.12 .

[0026] (3) 10 g of LiMn 0.5 Fe 0.5 PO4 / C in step (1) and 0.5 g of the modifier LaFeAsO 0.88 F 0.12 in step (2) are mixed and then ball-milled and mixed at 350 rpm for 1 h to obtain the modified lithium iron manganese phosphate cathode material.

[0027] Comparative Example 1 The cathode material is lithium iron manganese phosphate (LiMn 0.5 Fe 0.5PO4), and the preparation method is basically the same as step (1) in Example 1, except that: PVP is not added in step (1).

[0028] Comparative Example 2 The cathode material is carbon-containing lithium manganese iron phosphate (LiMn 0.5 Fe 0.5 PO4 / C), and the preparation method is the same as step (1) in Example 1.

[0029] Comparative Example 3 In this example, a modified lithium manganese iron phosphate cathode material is prepared, including lithium manganese iron phosphate and a modifier LaFeAsO 0.88 F 0.12 .

[0030] The preparation method is basically the same as that in Example 1, except that: PVP is not added in step (1) of the preparation method, and correspondingly, LiMn 0.5 Fe 0.5 PO4 is prepared.

[0031] Example 2 It is basically the same as Example 1, except that: the addition amount of the modifier LaFeAsO 0.88 F 0.12 in step (3) is 0.3 g.

[0032] Example 3 It is basically the same as Example 1, except that: the addition amount of the modifier LaFeAsO 0.88 F 0.12 in step (3) is 0.8 g.

[0033] Example 4 In this example, a modified lithium manganese iron phosphate cathode material is prepared, including a composite material composed of lithium manganese iron phosphate and carbon (LiMn 0.6 Fe 0.4 PO4 / C) and a modifier CeFeAsO 0.8 F 0.2 . The specific preparation method is as follows: (1) 0.24 mol of manganese acetate, 0.16 mol of ferrous acetate, 0.406 mol (26.8 g) of lithium acetate, and 0.268 g of starch were dispersed in 400 ml of deionized water to form a metal salt solution. Another certain amount of 0.4 mol of (NH4)2HPO4 was dissolved in 200 ml of deionized water to form a phosphate solution. Under stirring conditions, the phosphate solution was added to the metal salt solution, and then heated at 60 °C for 24 h to fully react, obtaining a lithium iron manganese phosphate precursor. After drying the lithium iron manganese phosphate precursor at 100 °C for 20 h, a dry gel-like lithium iron manganese phosphate precursor material was obtained. After the dry gel-like lithium iron manganese phosphate precursor material was ball-milled and pulverized, it was sintered at 800 °C for 30 h under a nitrogen atmosphere, obtaining a composite material composed of lithium iron manganese phosphate and carbon (LiMn 0.6 Fe 0.4 PO4 / C).

[0034] (2) 0.028 mol of CeAs, 0.002 mol of FeAs, 0.012 mol of Fe, 0.002 mol of CeF3, and 0.007 mol of Fe2O3 materials were weighed in proportion, and after ball-milling and solid-phase mixing, a mixed powder was obtained. The mixed powder was transferred into a magnetic boat and sintered at 850 °C for 30 h under an oxygen atmosphere, obtaining a modifier CeFeAsO 0.8 F 0.2 .

[0035] (3) 10 g of LiMn 0.6 Fe 0.4 PO4 / C in step (1) and 0.5 g of the modifier CeFeAsO 0.8 F 0.2 were ball-milled and mixed at a rotation speed of 300 rpm for 2 h, obtaining a modified lithium iron manganese phosphate cathode material.

[0036] Example 5 In this example, a modified lithium iron manganese phosphate cathode material was prepared, including a composite material composed of lithium iron manganese phosphate and carbon (LiMn 0.1 Fe 0.9 PO4 / C) and a modifier NdFeAsO 0.9 F 0.1 . The specific preparation method is as follows: (1) 0.04 mol of manganese acetate, 0.36 mol of ferrous acetate, 0.408 mol (26.9 g) of lithium acetate, and 0.8 g of glucose were dispersed in 400 ml of deionized water to form a metal salt solution. Separately, a certain amount of 0.4 mol of (NH4)2HPO4 was dissolved in 200 ml of deionized water to form a phosphate solution. Under stirring conditions, the phosphate solution was added to the metal salt solution. Then, after heating at 90 °C for 16 h with sufficient reaction, a lithium iron manganese phosphate precursor was obtained. After drying the lithium iron manganese phosphate precursor at 100 °C for 20 h, a dry gel-like lithium iron manganese phosphate precursor material was obtained. After the dry gel-like lithium iron manganese phosphate precursor material was ball-milled and pulverized, it was sintered at 1000 °C for 10 h under a nitrogen atmosphere to obtain a composite material composed of lithium iron manganese phosphate and carbon (LiMn 0.1 Fe 0.9 PO4 / C).

[0037] (2) 0.029 mol of NdAs, 0.001 mol of FeAs, 0.011 mol of Fe, 0.001 mol of NdF3, and 0.009 mol of Fe2O3 materials were weighed in proportion, and after ball-milling and solid-phase mixing, a mixed powder was obtained. The mixed powder was transferred into a magnetic boat and sintered at 1000 °C for 10 h under an oxygen atmosphere to obtain the modifier NdFeAsO 0.9 F 0.1 .

[0038] (3) 10 g of LiMn 0.1 Fe 0.9 PO4 / C from step (1) and 0.5 g of the modifier NdFeAsO 0.9 F 0.1 were ball-milled and mixed at a rotation speed of 500 rpm for 0.5 h to obtain a modified lithium iron manganese phosphate cathode material.

[0039] The cathode materials prepared in Examples 1 - 5 and Comparative Examples 1 - 3 were assembled into batteries by the following method: The cathode materials prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were respectively mixed with conductive agent acetylene black (AB) and binder polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1. Using N-methylpyrrolidone (NMP) as the solvent, the mixture was placed in a small beaker and stirred at a speed of 800 r / min for 2 h to obtain a slurry. The slurry was coated on the current collector aluminum foil using an automatic coater, laid flat on tempered glass, and transferred to a vacuum drying oven at 85 °C for drying for 4 h. Then, it was punched into a pole piece with a diameter of 12 mm. The pole piece was dried in a vacuum drying oven at 105 °C for 4 h, and then placed in a glove box filled with argon gas with a water content and oxygen content both lower than 0.1 ppm for 4 h to reduce the moisture adsorbed by the pole piece during the transfer process. Then, it was assembled into a CR2032 type button cell in the glove box. The battery used a pure metal lithium sheet with a diameter of 16 mm and a thickness of 0.5 mm as the negative electrode, a porous polyethylene membrane with a diameter of 18 mm and a model of Celgard 2300 as the separator, and a 1 M LiPF6 solution as the electrolyte (the solvent of the electrolyte was composed of DEC, EC, and DMC with a volume ratio of 1:1:1).

[0040] After the battery assembly was completed, it was aged for 12 h. At 25 °C and a voltage of 2 - 4.4 V, after being activated for 3 cycles at a current density of 0.1 C, it was then cycled 100 times at a current density of 2 C. The test results are as Figure 1 shown.

[0041] From Figure 1 it can be seen that the battery assembled with the unmodified lithium iron manganese phosphate cathode material in Comparative Example 1 has poor cycle stability. Compared with the battery in Comparative Example 1, the battery assembled with the carbon-modified lithium iron manganese phosphate cathode material in Comparative Example 2 has improved cycle performance, but the improvement is very limited. Compared with the battery in Comparative Example 1, the battery assembled with the LaFeAsO 0.88 F 0.12 -modified lithium iron manganese phosphate cathode material in Comparative Example 3 also has improved cycle performance, but the improvement is also very limited. However, compared with the batteries assembled with the cathode materials in Comparative Examples 1 to 3, the battery assembled with the modified lithium iron manganese phosphate cathode material in Example 1 has a significantly improved cycle performance.

[0042] Compared with the battery assembled with the modified lithium iron manganese phosphate cathode material in Example 1, the batteries assembled with the modified lithium iron manganese phosphate cathode materials in Example 2 and Example 3 have certain changes in performance, but both have good electrochemical performance.

[0043] By adjusting the material components and process parameters in Example 4 and Example 5, the performance of the batteries assembled with the corresponding prepared cathode materials has certain changes, but both have good electrochemical performance.

[0044] The batteries assembled with the cathode materials of Example 1 and Comparative Example 2 were activated at a current density of 0.1C for 3 cycles at 0 °C and a voltage of 2 - 4.4V, and then cycled 100 times at a current density of 1C. The test results are shown in Figure 2 .

[0045] It can be seen from Figure 2 that the battery assembled with the carbon-modified lithium iron manganese phosphate cathode material in Comparative Example 2 has very poor cycling performance at 0 °C; while the battery assembled with the lithium iron manganese phosphate cathode material co-modified with carbon and LaFeAsO 0.88 F 0.12 in Example 1 has relatively stable cycling performance.

[0046] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A modified lithium iron manganese phosphate cathode material, characterized in that, The positive electrode material is a composite material composed of lithium iron manganese phosphate and carbon and a modifier MFeAsO x F 1-x a mixture formed; wherein: M is one of La, Nd, Ce, and Pr, and 0.8 ≤ x ≤ 0.

9.

2. The modified lithium iron manganese phosphate cathode material according to claim 1, characterized in that The chemical formula of the composite material composed of lithium iron manganese phosphate and carbon is LiMn y Fe 1-y PO4 / C, where: 0.1 ≤ y ≤ 0.

6.

3. The modified lithium iron manganese phosphate cathode material according to claim 1 or 2, characterized in that, The composite material composed of lithium iron manganese phosphate and carbon and the modifier MFeAsO x F 1-x has a mass ratio of 1:(0.03~0.08).

4. A method for preparing the modified lithium iron manganese phosphate cathode material according to any one of claims 1 to 3, characterized in that, comprising the following steps: A composite material composed of lithium iron manganese phosphate and carbon is solid-phase mixed with a modifier MFeAsO x F 1-x to obtain a modified lithium iron manganese phosphate cathode material.

5. The preparation method of the modified lithium iron manganese phosphate cathode material according to claim 4, characterized in that, The preparation method of the composite material composed of lithium iron manganese phosphate and carbon comprises the following steps: dispersing a manganese source, an iron source, a lithium source, and a carbon source in deionized water to form a metal salt solution, and dissolving a phosphate in water to form a phosphate solution; adding the phosphate solution to the metal salt solution, and after heating and reacting, obtaining a lithium iron manganese phosphate precursor material; sintering the lithium iron manganese phosphate precursor material in an inert atmosphere to obtain the composite material composed of lithium iron manganese phosphate and carbon.

6. The preparation method of the modified lithium iron manganese phosphate cathode material according to claim 5, wherein the manganese source is one or two of manganese acetate and manganese nitrate; the iron source is one or two of ferrous acetate and ferrous nitrate; the lithium source is one or two of lithium nitrate and lithium acetate; the carbon source is one or more of glucose, starch, and polyvinylpyrrolidone; the phosphate is one or two of diammonium hydrogen phosphate and ammonium dihydrogen phosphate; The molar ratios of Li, Mn, Fe and PO4 in the lithium source, manganese source, iron source and phosphate 3- are (1.01~1.04):y:(1-y):1, where 0.1≤y≤0.6; the mass ratio of the lithium source to the carbon source is 1:(0.01~0.03).

7. The preparation method of the modified lithium iron manganese phosphate cathode material according to claim 5, characterized in that, the temperature of the heating reaction is 60-90 °C, and the time of the heating reaction is 10-24 h; the inert atmosphere is a nitrogen or argon atmosphere; the sintering temperature is 800-1000 °C, and the sintering time is 10-30 h.

8. The preparation method of the modified lithium iron manganese phosphate cathode material according to claim 4, characterized in that, The modifier MFeAsO x F 1-x The preparation method thereof comprises the following steps: After ball-milling and solid-phase mixing of raw materials MAs, FeAs, Fe, MF3, and Fe2O3, a mixed powder is obtained. The mixed powder is sintered in an oxygen-containing atmosphere to obtain the modifier MFeAsO x F 1-x 。 9. The preparation method of the modified lithium iron manganese phosphate cathode material according to claim 8, characterized in that, the oxygen-containing atmosphere is an oxygen atmosphere or an air atmosphere, the sintering temperature is 850-1000 °C, and the sintering time is 10-30 h.

10. A lithium ion battery, comprising the modified lithium iron manganese phosphate cathode material according to any one of claims 1-3, or the modified lithium iron manganese phosphate cathode material prepared by the preparation method according to any one of claims 4-9.

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