阅读说明：本技术 一种改性磷酸锰铁锂正极材料，其制备方法及锂离子电池 (Modified lithium iron manganese phosphate cathode material, preparation method thereof and lithium ion battery ) 是由 张秀奎 陈梦婷 李芳芳 赵成龙 王正伟 于 2021-08-10 设计创作，主要内容包括：本发明公开了一种改性磷酸锰铁锂正极材料的制备方法,包括：a.将微米级的磷酸锰铁锂、分散剂进行纳米化,得到纳米级的磷酸锰铁锂浆料；将微米级的固态电解质进行纳米化,得到纳米级固态电解质浆料；b.将磷酸锰铁锂浆料和固态电解质浆料烘干,再混合均匀,得到复合材料；c.将复合材料在惰性气氛下进行煅烧,得到改性磷酸锰铁锂正极材料；其中,分散剂为聚乙烯吡咯烷酮、聚乙二醇、聚乙烯醇中的一种或多种,其添加量为磷酸锰铁锂的1wt％～5wt％；改性磷酸锰铁锂正极材料中固态电解质的含量为0.3wt％～3wt％。本发明的改性磷酸锰铁锂正极材料,能够改善磷酸锰铁锂电子和离子电导率低的问题,更好的构筑电子和离子通道,提高循环性能。(The invention discloses a preparation method of a modified lithium iron manganese phosphate anode material, which comprises the following steps: a. carrying out nanocrystallization on the micron-sized lithium manganese iron phosphate and a dispersing agent to obtain a nanoscale lithium manganese iron phosphate slurry; carrying out nanocrystallization on the micron-sized solid electrolyte to obtain nanoscale solid electrolyte slurry; b. drying the lithium iron manganese phosphate slurry and the solid electrolyte slurry, and uniformly mixing to obtain a composite material; c. calcining the composite material in an inert atmosphere to obtain a modified lithium iron manganese phosphate anode material; wherein the dispersant is one or more of polyvinylpyrrolidone, polyethylene glycol and polyvinyl alcohol, and the addition amount of the dispersant is 1 to 5 weight percent of the manganese lithium iron phosphate; the content of the solid electrolyte in the modified lithium iron manganese phosphate anode material is 0.3 wt% -3 wt%. The modified lithium iron manganese phosphate cathode material can solve the problem of low electronic and ionic conductivity of lithium iron manganese phosphate, better constructs electronic and ionic channels and improves the cycle performance.)

1. A preparation method of a modified lithium iron manganese phosphate cathode material is characterized by comprising a method A or a method B;

the method A comprises the following steps:

a. carrying out nanocrystallization on the micron-sized lithium manganese iron phosphate and a dispersing agent to obtain a nanoscale lithium manganese iron phosphate slurry; carrying out nanocrystallization on the micron-sized solid electrolyte to obtain nanoscale solid electrolyte slurry;

b. drying the lithium iron manganese phosphate slurry obtained in the step a and the solid electrolyte slurry, and then uniformly mixing to obtain a composite material;

c. calcining the composite material obtained in the step b in an inert atmosphere to obtain a modified lithium iron manganese phosphate anode material;

the method B comprises the following steps:

d. simultaneously carrying out nanocrystallization on the micron-sized lithium manganese iron phosphate, the solid electrolyte and the dispersing agent to obtain composite slurry;

e. drying the composite slurry obtained in the step d to obtain a composite material;

f. calcining the composite material obtained in the step e in an inert atmosphere to obtain a modified lithium iron manganese phosphate anode material;

in the method A and the method B, the dispersing agent is one or more of polyvinylpyrrolidone, polyethylene glycol and polyvinyl alcohol, and the addition amount of the dispersing agent is 1 to 5 weight percent of the manganese lithium iron phosphate;

in the modified lithium iron manganese phosphate cathode material, the content of solid electrolyte is 0.3 wt% -3 wt%.

2. The method for preparing the modified lithium iron manganese phosphate cathode material of claim 1, wherein the lithium iron manganese phosphate is LiMn_0.5Fe_0.5PO₄、LiMn_0.6Fe_0.4PO₄、LiMn_0.7Fe_0.3PO₄、LiMn_0.8Fe_0.2PO₄、LiMn_0.9Fe_0.1PO₄One kind of (1).

3. The method for preparing the modified lithium iron manganese phosphate cathode material according to claim 1, wherein D of the lithium iron manganese phosphate is₅₀1 to 10 μm.

4. The method for preparing a modified lithium iron manganese phosphate cathode material according to claim 1, wherein the solid electrolyte is one of lithium aluminum titanium phosphate, lithium lanthanum titanate and lithium lanthanum zirconium oxide.

5. The method for preparing the modified lithium iron manganese phosphate cathode material according to claim 1, wherein D of the solid electrolyte is₅₀5 to 100 μm.

6. The preparation method of the modified lithium iron manganese phosphate cathode material as claimed in claim 1, wherein in the steps a and d, a sand mill is adopted for nanocrystallization, the diameter of a zirconia ball used in sand milling is 0.3mm, the mass ratio of the zirconia ball, the material and water is 10:1, the rotation speed of the sand mill is 2000r/min, and the grinding time is 30-120 min.

7. The preparation method of the modified lithium iron manganese phosphate cathode material according to claim 1, wherein in the steps b and e, the drying temperature is 100-150 ℃ and the drying time is 30 min-2 h.

8. The preparation method of the modified lithium iron manganese phosphate cathode material as claimed in claim 6, wherein in the steps c and f, the inert atmosphere is nitrogen or argon, the calcination temperature is 800-1000 ℃, and the calcination time is 4-10 hours.

9. The modified lithium iron manganese phosphate cathode material prepared by the method of any one of claims 1 to 8.

10. A lithium ion battery, comprising a positive plate, a negative plate, electrolyte and a diaphragm, characterized in that the positive plate is prepared from the modified lithium iron manganese phosphate positive material of claim 9.

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a modified lithium iron manganese phosphate cathode material, a preparation method thereof and a lithium ion battery.

Background

Lithium iron manganese phosphate material (LiMn)_1-xFe_xPO₄(0<x<1) Has the characteristics of rich raw materials, low cost, higher specific capacity, good thermal stability and the like, and is compared with lithium iron phosphate (LiFePO)₄) The lithium ion battery cathode material has higher discharge voltage (3.8V vs3.3V), so that the energy density of the battery can be improved by about 15 percent, and the lithium ion battery cathode material is one of the new-generation industrialized lithium ion battery cathode materials. However, lithium iron manganese phosphate has low electronic conductivity, low lithium ion diffusion coefficient, two voltage plateaus (4.1V and 3.4V) and Mn³⁺The Jahn-Teller effect and other defects limit the large-scale application of the method.

By modifying the lithium manganese iron phosphate, a high-speed ion transmission channel is established on the basis of carbon coating, polarization is reduced, and the cycle performance of the lithium manganese iron phosphate can be effectively improved. The current commonly used modification method comprises particle size nanocrystallization, morphology control, conductive phase carbon coating, ion doping and the like, and the performance of the lithium iron manganese phosphate anode material can be greatly improved after the three aspects of comprehensive modification. For example, chinese patent publication No. CN103762362A discloses a hydrothermal preparation method of a nano lithium iron manganese phosphate cathode material, which adopts a hydrothermal method and a spray drying method to prepare a titanium-doped lithium manganese phosphate cathode material. However, the method adopts one-step hydrothermal synthesis of the composite material, which easily causes large consumption of the lithium source, and the spray drying has high requirements on production equipment and large energy consumption. The Chinese patent with publication number CN110247044A discloses a graphene in-situ composite lithium manganese iron phosphate cathode material and a preparation method thereof, the growth of crystal grains is effectively controlled by coating of graphene, the crystal grains in the material are orderly arranged and are densely stacked, and the structural stability of the electrode material is maintained; meanwhile, the excellent conductivity of the graphene accelerates the electron transfer rate of the composite material, and effectively improves the conductivity of the electrode material. However, the scheme only considers the electronic conductivity of the lithium manganese iron phosphate, the ionic conductivity of the material is not well improved, and the graphene is expensive and has high cost. Chinese patent publication No. CN111477862A discloses a carbon-coated lithium manganese iron phosphate positive electrode material for a lithium ion battery and a preparation method thereof, wherein biological rapeseed pollen is used as a template, and a high-pressure hot solvent method and a high-temperature thermal cracking method are used to prepare porous lithium manganese iron phosphate, so that the lithium manganese iron phosphate forms a rich pore structure, which is beneficial to diffusion and transmission of lithium ions and improves the diffusion rate of the lithium ions. However, the method also has the problems of large consumption of lithium resources, poor regulation of porosity and the like.

The above methods do not take into account the electronic conductivity and ionic conductivity of the lithium iron manganese phosphate material, as well as the problems of cost, industrialization and the like, so that a modified lithium iron manganese phosphate positive electrode material and a preparation method thereof are required to overcome the technical and cost problems and obtain the modified lithium iron manganese phosphate positive electrode material which has excellent performance, low cost and is easy for large-scale production.

Disclosure of Invention

The invention aims to provide a modified lithium manganese iron phosphate cathode material, which is obtained by modifying lithium manganese iron phosphate through a nano-scale solid electrolyte and a carbonized dispersing agent, has high electronic and ionic conductivity and small polarization, and can improve the performance of a lithium manganese iron phosphate lithium battery when applied to the lithium ion battery.

The invention provides a preparation method of a modified lithium iron manganese phosphate anode material, which comprises a method A or a method B;

the method A comprises the following steps:

a. carrying out nanocrystallization on the micron-sized lithium manganese iron phosphate and a dispersing agent to obtain a nanoscale lithium manganese iron phosphate slurry; carrying out nanocrystallization on the micron-sized solid electrolyte to obtain nanoscale solid electrolyte slurry;

b. drying the lithium iron manganese phosphate slurry obtained in the step a and the solid electrolyte slurry, and then uniformly mixing to obtain a composite material;

c. calcining the composite material obtained in the step b in an inert atmosphere to obtain a modified lithium iron manganese phosphate anode material;

the method B comprises the following steps:

d. simultaneously carrying out nanocrystallization on the micron-sized lithium manganese iron phosphate, the solid electrolyte and the dispersing agent to obtain composite slurry;

e. drying the composite slurry obtained in the step d to obtain a composite material;

f. calcining the composite material obtained in the step e in an inert atmosphere to obtain a modified lithium iron manganese phosphate anode material;

in the method A and the method B, the dispersing agent is one or more of polyvinylpyrrolidone, polyethylene glycol and polyvinyl alcohol, and the addition amount of the dispersing agent is 1 wt% -5 wt% of the lithium manganese iron phosphate, and preferably 2 wt%.

In the modified lithium iron manganese phosphate cathode material, the content of the solid electrolyte is 0.3 wt% -3 wt%, and preferably 1.5 wt%.

After sanding treatment, the particle size of the lithium manganese iron phosphate is 300-800 nm, and the particle size of the solid electrolyte is 50-300 nm. According to the invention, the micro-scale lithium manganese iron phosphate is subjected to sanding and nanocrystallization treatment and then is mixed with the solid electrolyte to prepare the slurry, and the nano-scale lithium manganese iron phosphate particles enable a lithium ion deintercalation path to be shorter and an ion diffusion coefficient to be higher.

In the invention, the molecular formula of the lithium manganese iron phosphate is LiMn_xFe_1-xPO₄(0<x<1) Including but not limited to LiMn_0.5Fe_0.5PO₄、LiMn_0.6Fe_0.4PO₄、LiMn_0.7Fe_0.3PO₄、LiMn_0.8Fe_0.2PO₄、LiMn_0.9Fe_0.1PO₄One kind of (1).

In the invention, D of the micron-sized lithium manganese iron phosphate₅₀Preferably 1 to 10 μm.

In the present invention, the solid electrolyte may be selected from solid electrolytes commonly used in the art, including but not limited to one or more of Lithium Aluminum Titanium Phosphate (LATP), Lithium Lanthanum Titanate (LLTO), Lithium Lanthanum Zirconium Oxide (LLZO).

In the present invention, D of the micron-sized solid electrolyte₅₀Preferably 5 to 100 μm.

Further, in the steps a and d, a sand mill is adopted for nanocrystallization, the diameter of a zirconia ball used in sand milling is 0.3mm, the mass ratio of the zirconia ball to the materials to water is 10:1, the rotating speed of the sand mill is 2000r/min, and the grinding time is 30-120 min. The zirconia ball is small, the ball material ratio is high, the specific surface area of the ball is large, the contact grinding points of the ball material are more, meanwhile, the sand mill has high rotating speed and large linear speed, the kinetic energy obtained by the ball is large, the shearing, extruding and stripping capabilities of the ball are strong, and the lithium manganese iron phosphate and the solid electrolyte can be fully crushed.

Further, in the steps b and e, the drying temperature is 100-150 ℃, and the drying time is 30 min-2 h.

Further, in the steps c and f, the inert atmosphere is nitrogen or argon, the calcining temperature is 800-1000 ℃, and the calcining time is 4-10 hours. The invention adopts the calcination at a high temperature of 800-1000 ℃ to mainly improve the graphitization degree of the dispersant. The higher the carbonization temperature of the dispersing agent is, the higher the graphitization degree of the dispersing agent is, and the higher the graphitization degree is, the conductivity of the material can be improved, and in addition, the resistance of the grain boundary of the solid electrolyte during high-temperature calcination is smaller, so that the high-temperature calcination can be beneficial to improving the ionic conductivity of the cathode material.

The invention also provides the modified lithium iron manganese phosphate anode material prepared by the method.

The invention also provides a lithium ion battery which comprises a positive plate, a negative plate, electrolyte and a diaphragm, wherein the positive plate is prepared from the modified lithium iron manganese phosphate positive material.

Compared with the prior art, the technical scheme of the invention has the following advantages:

1. the invention creatively introduces the solid electrolyte into the anode material, firstly uses a sand mill to carry out nanocrystallization on the solid electrolyte and the lithium manganese iron phosphate, uses a dispersing agent to ensure that the lithium manganese iron phosphate and the solid electrolyte are better and uniformly mixed, and utilizes the characteristics of high electronic conductivity, small internal resistance and high ionic conductivity of the nano solid electrolyte of the lithium manganese iron phosphate with the nano structure to reduce the polarization and manganese dissolution of the lithium manganese iron phosphate and improve the cycle performance.

2. According to the invention, through high-temperature calcination, the dispersing agent is carbonized into a carbon material coated on the surface of the lithium manganese iron phosphate, so that the electronic conductivity of the lithium manganese iron phosphate material is improved on one hand, the contact between active substances is further improved on the other hand, the side reaction between the active substances and the electrolyte is reduced, and the cycle and rate performance of the material are improved.

3. The invention adopts different preparation methods simultaneously, can ensure that the lithium manganese iron phosphate, the solid electrolyte and the dispersing agent can fully play a role in a synergistic manner, simultaneously solves the problem of low electronic and ionic conductivity of the lithium manganese iron phosphate, better constructs electronic and ionic channels and improves the cycle performance.

Drawings

Fig. 1 is a flow chart of a preparation process of the modified lithium iron manganese phosphate cathode material of the present invention;

fig. 2 is a 1C cycle chart of the button cell prepared in example 1 and comparative example 1;

fig. 3 is a graph comparing the cycle life of square aluminum cell prepared in example 2 and comparative example 2.

Detailed Description

The present invention is further described below in conjunction with specific examples to enable those skilled in the art to better understand the present invention and to practice it, but the examples are not intended to limit the present invention.

Example 1

The embodiment provides a preparation method of a modified lithium iron manganese phosphate positive electrode material, which comprises the following steps:

(1) adding 1kg of lithium manganese iron phosphate, 30g of polyethylene glycol and 1.4kg of deionized water into a sand mill for sanding, wherein the lithium manganese iron phosphate is LiMn_0.8Fe_0.2PO₄Particle size 2.5 μm, oxidation in a sand millThe diameter of the zirconium ball is 0.3mm, the mass ratio of the zirconium oxide ball to the materials is 10:1, and the rotating speed of the sand mill is 2000 r/min. Grinding for 30min to obtain nanoscale lithium iron manganese phosphate slurry, and testing the particle size D of the slurry₅₀Is 200 nm. And then drying the lithium iron manganese phosphate slurry in a vacuum box at the drying temperature of 100 ℃ for 1h to obtain the nano lithium iron manganese phosphate (containing the dispersing agent).

(2) 1kg of LATP and 1.4kg of deionized water are added into a sand mill for sand milling, wherein the particle size of the LATP is 50 mu m, the diameter of a zirconia ball in the sand mill is 0.3mm, the mass ratio of the zirconia ball to the materials is 10:1, and the rotating speed of the sand mill is 2000 r/min. Grinding for 30min to obtain nanoscale solid electrolyte slurry, and testing particle size D₅₀Is 500 nm. And then drying the solid electrolyte slurry in a vacuum box at the drying temperature of 120 ℃ for 1h to obtain the nano lithium aluminum titanium phosphate.

(3) Sintering 500g of nano lithium manganese iron phosphate (containing a dispersing agent) and 5g of nano LATP at 800 ℃ for 5 hours in a nitrogen atmosphere, wherein the heating rate is 5 ℃/min, and cooling along with a furnace to obtain a modified lithium manganese iron phosphate anode material D₅₀Is 1 μm.

The button cell assembled by the material is tested under the condition of 1C, and the capacity retention rate of 200 circles is 97.5%.

Example 2

(1) Adding 1kg of lithium manganese iron phosphate, 10g of LATP, 30g of polyvinyl alcohol and 1.7kg of deionized water into a sand mill for sanding, wherein the lithium manganese iron phosphate is LiMn_0.7Fe_0.3PO₄The grain diameter is 2.5 mu m, the diameter of zirconia balls in a sand mill is 0.3mm, the mass ratio of the zirconia balls to materials is 10:1, and the rotating speed of the sand mill is 2000 r/min. Grinding for 30min to obtain nanometer composite slurry, and testing its particle size D₅₀Is 300 nm. And then drying the composite slurry in a vacuum box at the drying temperature of 120 ℃ for 1h to obtain the nano composite material.

(2) Sintering 500g of the nano composite material at 800 ℃ for 5h in a nitrogen atmosphere, wherein the heating rate is 5 ℃/min, and cooling along with a furnace to obtain a modified lithium iron manganese phosphate anode material D₅₀Is 2 μm.

The button cell assembled by the material is tested under the condition of 1C, and the capacity retention rate of 200 circles is 99%.

The material is used as a positive electrode material to assemble a square aluminum shell lithium ion battery, the thickness of the battery is 21mm, the width of the battery is 115mm, the height of the battery is 108mm, the designed capacity is 22Ah, 19.7Ah of capacity remains after the battery is cycled for 800 times at normal temperature, and the capacity retention rate is 89.5%.

Comparative example 1

(1) Adding 1kg of lithium manganese iron phosphate, 30g of polyethylene glycol and 1.4kg of deionized water into a sand mill for sanding, wherein the lithium manganese iron phosphate is LiMn_0.8Fe_0.2PO₄The grain diameter is 2.5 mu m, the diameter of zirconia balls in a sand mill is 0.3mm, the mass ratio of the zirconia balls to materials is 10:1, and the rotating speed of the sand mill is 2000 r/min. Grinding for 30min to obtain nanoscale lithium iron manganese phosphate slurry, and testing the particle size D of the slurry₅₀Is 200 nm. And then drying the lithium iron manganese phosphate slurry in a vacuum box at the drying temperature of 100 ℃ for 1h to obtain the nano lithium iron manganese phosphate (containing the dispersing agent).

(2) Sintering 500g of nano lithium manganese iron phosphate (containing a dispersing agent) at 800 ℃ for 5h in a nitrogen atmosphere, wherein the heating rate is 5 ℃/min, and cooling along with a furnace to obtain a modified lithium manganese iron phosphate cathode material D₅₀And was 1.5 μm.

The button cell assembled by the material is tested under the condition of 1C in a circulating way, and the capacity retention rate of 200 circles is 95%.

Comparative example 2

(1) Adding 1kg of lithium manganese iron phosphate, 100g of LATP and 1.7kg of deionized water into a sand mill for sanding, wherein the lithium manganese iron phosphate is LiMn_0.7Fe_0.3PO₄The grain diameter is 2.5 mu m, the diameter of zirconia balls in a sand mill is 0.3mm, the mass ratio of the zirconia balls to materials is 10:1, and the rotating speed of the sand mill is 2000 r/min. Grinding for 30min to obtain nanometer composite slurry, and testing its particle size D₅₀Is 250 nm. And then drying in a vacuum box at the drying temperature of 120 ℃ for 1h to obtain the nano composite lithium iron manganese phosphate anode material.

(2) 500g of nano composite manganese iron phosphateSintering the lithium material at 800 ℃ in a nitrogen atmosphere for 5h at the heating rate of 5 ℃/min, and cooling the lithium material along with the furnace to obtain a modified lithium iron manganese phosphate anode material D₅₀2.5 mu m, and the button cell assembled by the material is tested under the condition of 1C for 200 circles of capacity retention rate of 96 percent.

The material is used as a positive electrode material to assemble a square aluminum shell lithium ion battery, the thickness of the battery is 21mm, the width of the battery is 115mm, the height of the battery is 108mm, the designed capacity is 22Ah, 18.4Ah of capacity remains after the battery is cycled for 800 times at normal temperature, and the capacity retention rate is 83.6%.

Comparing example 1 with comparative example 1, it can be seen that the button cell of example 1 tested under the condition of 1C has a capacity retention rate of 97.5% at 200 cycles, while comparative example 1 only has a capacity retention rate of 95%. The solid electrolyte is added into the lithium iron manganese phosphate positive electrode material in the embodiment 1, so that the ionic conductivity of the lithium iron manganese phosphate is improved, the polarization and manganese dissolution of the lithium iron manganese phosphate are reduced, and the cycle performance is improved.

Comparing example 2 with comparative example 2, it can be seen that the button cell of example 2 tested under the condition of 1C has a capacity retention rate of 99% at 200 cycles, and the capacity retention rate of comparative example 2 is only 96%. The full cell of example 2 tested under 1C conditions, the capacity retention after 800 cycles was 89.5%, while comparative example 2 was only 83.6%. The dispersing agent is added in the preparation process of the lithium manganese iron phosphate positive electrode material in the embodiment 2, so that the lithium manganese iron phosphate and the solid electrolyte are well and uniformly mixed, and in the calcining process, the dispersing agent is carbonized into a carbon material coated on the surface of the lithium manganese iron phosphate, so that the electronic conductivity of the lithium manganese iron phosphate material is improved on one hand, the contact between active substances is further improved on the other hand, the side reaction between the active substances and the electrolyte is reduced, and the cycle performance and the rate capability of the material are improved.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.