Positive electrode material for lithium ion battery and preparation method of positive electrode material

Abstract

The invention discloses a positive electrode material for a lithium ion battery, which is characterized in that the positive electrode material comprises a composite lithium-rich manganese-based positive electrode material active substance, a composite conductive agent, a current collector and a binder, the composite lithium-rich manganese-based positive electrode material active substance is a mixture of a lithium-rich manganese-based positive electrode material and lithium iron phosphate; the composite conductive agent is a mixture of carbon black, graphene and carbon nanotubes; the binder is polyvinylidene fluoride, and the current collector is aluminum foil. The lithium-rich manganese-based positive electrode material and the lithium iron phosphate are combined as positive electrode active components, and the lithium iron phosphate is compounded with the lithium-rich manganese-based material by utilizing the excellent cycle stability brought by the olivine structure of the lithium iron phosphate, so that the overall cycle performance of the lithium ion battery is enhanced; a compound of carbon black, graphene and a carbon nano tube is used as a conductive additive, a synergistic effect is formed through mutual complementation of unique attributes of the materials, and the rapid charging and discharging capacity of the lithium ion battery is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of battery materials, more particularly, to a positive electrode material for lithium ion batteries and a preparation method thereof. BACKGROUND

[0002] In the field of lithium ion batteries, the selection of positive electrode materials is crucial as they directly relate to the performance, cost, and environmental impact of the battery. Traditional LiCoO2, while stable in performance, is costly and has limited capacity; LiNiO2 has unstable capacity due to ion mixing problems and requires harsh synthesis conditions; and LiFePO4 has good cycle stability, but its electrical conductivity and lithium ion diffusion coefficient are low, limiting its application range.

[0003] In recent years, lithium-rich manganese-based positive electrode materials xLi2MnO3·(1-x)LiMO2 have become a research hotspot due to their high discharge specific capacity, low cost, and environmental characteristics. However, the disappearance of oxygen vacancies during the first charge and discharge leads to low efficiency and poor cycle stability, and the presence of Li2MnO3 insulating phase reduces the electrical conductivity, affecting the rate performance. In addition, the structural phase change during charging and discharging also limits its development.

[0004] To improve these shortcomings, researchers have adopted various strategies, including optimizing the preparation process, carbon coating, nanocrystallization treatment, and selecting better conductive additives. For example, patent CN201410409799B proposes a preparation method for nano-structured high-rate lithium-rich manganese-based positive electrode materials, which improves the rate capacity by designing intrinsic carriers with short diffusion paths, and maintains the cycle performance by using the stability of microstructures. Although this method has made progress in improving performance, the preparation process is complex and the cycle stability still needs to be further improved.

[0005] Therefore, there is a need for a new type of positive electrode material for lithium ion batteries that can solve the above problems. SUMMARY

[0006] An object of the present application is to provide a new technical solution for a positive electrode material for lithium ion batteries.

[0007] According to a first aspect of the present application, a positive electrode material for lithium ion batteries is provided, comprising a composite lithium-rich manganese-based positive electrode material active substance, a composite conductive agent, a current collector, and a binder, the composite lithium-rich manganese-based positive electrode material active substance being a mixture of lithium-rich manganese-based positive electrode material and lithium iron phosphate; the composite conductive agent being a mixture of carbon black, graphene, and carbon nanotubes; the binder being polyvinylidene fluoride, and the current collector being aluminum foil.

[0008] Preferably, the mass ratio of carbon black, graphene, and carbon nanotubes is 8:1.5:2.5.

[0009] Preferably, the mass of the lithium-rich manganese-based positive electrode material in the composite lithium-rich manganese-based positive electrode material active substance is 75-85%, and the balance is lithium iron phosphate;

[0010] Preferably, the mass of the lithium-rich manganese-based positive electrode material in the composite lithium-rich manganese-based positive electrode material active substance is 77-82%, and the balance is lithium iron phosphate.

[0011] Preferably, the mass ratio of the composite lithium-rich manganese-based positive electrode material active substance, the composite conductive agent, and the binder is 85:15:15.

[0012] According to a second aspect of the present application, a preparation method of the above-mentioned positive electrode material for lithium ion batteries is provided, comprising the following steps:

[0013] Step 1: mixing the lithium-rich manganese-based positive electrode material and lithium iron phosphate uniformly to prepare a composite lithium-rich manganese-based positive electrode material active substance;

[0014] Step 2: mixing carbon black, graphene, and carbon nanotubes uniformly to prepare a composite conductive agent;

[0015] Step 3: dispersing the composite lithium-rich manganese-based positive electrode material active substance and the composite conductive agent uniformly in an organic solvent to obtain a mixed slurry, wherein the organic solvent is N-methyl pyrrolidone or the viscosity of the mixed slurry is 2000-9000 Pa.s;

[0016] Step 4: coating and drying the mixed slurry to obtain a composite lithium-rich manganese-based positive electrode material.

[0017] Preferably, the composite lithium-rich manganese-based positive electrode material active substance is added to the organic solvent in batches.

[0018] According to a third aspect of the present application, a lithium ion battery is provided, characterized in that the positive electrode material for lithium ion batteries according to any one of claims 1-5 is used as the positive electrode material of the lithium ion battery.

[0019] According to one embodiment of the present disclosure, the lithium-rich manganese-based positive electrode material and lithium iron phosphate are combined as the positive active ingredient, the superior cycle stability brought by the olivine structure of lithium iron phosphate is utilized, and the lithium-rich manganese-based material is compounded, which helps to enhance the overall cycle performance of the lithium ion battery; the composite of carbon black, graphene, and carbon nanotube is used as the conductive additive, and through the unique properties of these materials, a synergistic effect is formed, which effectively improves the rapid charge and discharge capability of the lithium ion battery.

[0020] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments thereof. DETAILED DESCRIPTION

[0021] Various exemplary embodiments of the present application will now be described in detail. It should be noted that the relative arrangement of components and steps, numerical expressions, and numerical values set forth in these embodiments are not meant to limit the scope of the present application unless otherwise specifically stated.

[0022] The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the scope of the application its application or uses.

[0023] Techniques, methods, and devices known to those of ordinary skill in the relevant art can not be discussed in detail herein. However, the techniques, methods, and devices should be considered part of the specification.

[0024] In all of the examples shown and discussed herein, any specific values should be interpreted as merely exemplary, and not as a limitation. Thus, other examples of exemplary embodiments can have different values.

[0025] According to one embodiment of the present application, a positive electrode material for a lithium ion battery comprises a composite lithium-rich manganese-based positive electrode material active substance, a composite conductive agent, a current collector, and a binder, wherein the composite lithium-rich manganese-based positive electrode material active substance is a mixture of a lithium-rich manganese-based positive electrode material and lithium iron phosphate; the composite conductive agent is a mixture of carbon black, graphene, and carbon nanotubes; and the binder is polyvinylidene fluoride, and the current collector is aluminum foil.

[0026] The mixture of carbon black, graphene, and carbon nanotubes reduces the impedance between the positive electrode active substance and the current collector, so as to improve the transmission efficiency between the current collector and the active substance using a smaller amount of conductive agent.

[0027] The binder not only plays a role in the composite lithium-rich manganese-based positive electrode material active substance, the composite conductive agent, and the current collector, but also prevents the composite lithium-rich manganese-based positive electrode material active substance from swelling and falling off during charging and discharging, and reduces the impedance between the current collector and the composite lithium-rich manganese-based positive electrode material active substance.

[0028] In one embodiment of the present application, the mass ratio of carbon black, graphene, and carbon nanotubes is 8:1.5:2.5.

[0029] In one embodiment of the present application, the mass of the lithium-rich manganese-based positive electrode material in the composite lithium-rich manganese-based positive electrode material active substance is 75-85%, and the remainder is lithium iron phosphate.

[0030] In one embodiment of the present application, the mass of the lithium-rich manganese-based positive electrode material in the composite lithium-rich manganese-based positive electrode material active substance is 77-82%, and the remainder is lithium iron phosphate.

[0031] In one embodiment of the present application, the mass ratio of the composite lithium-rich manganese-based positive electrode material active substance, the composite conductive agent, and the binder is 785:15:15.

[0032] In an embodiment of the present application, a preparation method of the above-mentioned positive electrode material for lithium ion battery is disclosed, comprising the following steps:

[0033] Step 1: uniformly mixing the lithium-rich manganese-based positive electrode material and lithium iron phosphate to prepare a composite lithium-rich manganese-based positive electrode material active substance;

[0034] In this step, the composite lithium-rich manganese-based positive electrode material active substance is ground for 90 minutes, and then the ground active substance is added to the mixed solution in 6-10 times to avoid agglomeration, and finally a composite lithium-rich manganese-based positive electrode material slurry with a viscosity of 5000 Pa.s is obtained.

[0035] The mixed solution is obtained by dissolving polyvinyl chloride (PVDF) in a certain amount of NMP.

[0036] Step 2: uniformly mixing carbon black, graphene and carbon nanotubes to prepare a composite conductive agent;

[0037] In this step, the carbon black, graphene and carbon nanotubes are ball milled for 4h. Then, the ball milled conductive agent is added to the stirred NMP, and the stirring is continued for 6h;

[0038] Step 3: uniformly dispersing the composite lithium-rich manganese-based positive electrode material active substance and the composite conductive agent in an organic solvent to obtain a mixed slurry, wherein the organic solvent is N-methyl pyrrolidone or the viscosity of the mixed slurry is 2000-9000 Pa.s;

[0039] Step 4: coating and drying the mixed slurry to obtain a composite lithium-rich manganese-based positive electrode material.

[0040] According to a third aspect of the present application, a lithium ion battery is provided, characterized in that the positive electrode material for lithium ion battery of any one of claims 1-5 is used as the positive electrode material of the lithium ion battery.

[0041] The lithium ion battery prepared by using the positive electrode material for lithium ion battery has the performance shown in Table 1 compared with the conventional battery:

[0042] Table 1: Performance comparison of the conventional battery and the battery in the present embodiment

[0043] Charge and discharge current Discharge capacity of prior art lithium ion batteries Discharge capacity of the lithium ion battery of this example 0.1C 247 248 0.5C 207 211 1C 166 179 2C 125 140 5C 70 85

[0044] As can be seen, the battery prepared by using the positive electrode material in the present embodiment has a larger discharge capacity under the same charge and discharge current.

[0045] The lithium-rich manganese-based positive electrode material and the lithium iron phosphate are combined as the positive active components, the superior cycle stability brought by the olivine structure of the lithium iron phosphate is utilized, the lithium-rich manganese-based material is compounded, and the overall cycle performance of the lithium ion battery is helped to be enhanced; the composite of the carbon black, the graphene and the carbon nanotube is used as the conductive additive, the unique properties of these materials are mutually supplemented, a synergistic effect is formed, and the fast charge and discharge capacity of the lithium ion battery is effectively improved.

[0046] Although some specific embodiments of the present application have been described in detail by examples, those skilled in the art should understand that the above examples are only for illustration, and are not intended to limit the scope of the present application. Those skilled in the art should understand that the above embodiments can be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A positive electrode material for lithium-ion batteries, characterized in that, The material includes a composite lithium-rich manganese-based cathode material active material, a composite conductive agent, a current collector, and a binder. The composite lithium-rich manganese-based cathode material active material is a mixture of lithium-rich manganese-based cathode material and lithium iron phosphate. The composite conductive agent is a mixture of carbon black, graphene, and carbon nanotubes. The binder is polyvinylidene fluoride, and the current collector is aluminum foil.

2. The cathode material for lithium-ion batteries as described in claim 1, characterized in that, The mass ratio of carbon black, graphene, and carbon nanotubes is 8:1.5:2.

5.

3. The positive electrode material for lithium-ion batteries as described in claim 1, characterized in that, The active material of the composite lithium-rich manganese-based cathode material comprises 75-85% lithium-rich manganese-based cathode material by mass, with the remainder being lithium iron phosphate.

4. The positive electrode material for lithium-ion batteries as described in claim 3, characterized in that, The active material of the composite lithium-rich manganese-based cathode material contains 77-82% lithium-rich manganese-based cathode material by mass, with the remainder being lithium iron phosphate.

5. The positive electrode material for lithium-ion batteries as described in claim 1, characterized in that, The mass ratio of active material, composite conductive agent, and binder in the composite lithium-rich manganese-based cathode material is 85:15:

15.

6. A method for preparing a positive electrode material for a lithium-ion battery according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Mix lithium-rich manganese-based cathode material with lithium iron phosphate to prepare composite lithium-rich manganese-based cathode material active material; Step 2: Mix carbon black, graphene and carbon nanotubes evenly to prepare a composite conductive agent; Step 3: The active material of the composite lithium-rich manganese-based cathode material and the composite conductive agent are dispersed evenly in an organic solvent to obtain a mixed slurry. The organic solvent is N-methylpyrrolidone or the viscosity of the mixed slurry is 2000-9000 Pa·s. Step 4: After coating and drying the mixed slurry, the composite lithium-rich manganese-based cathode material is obtained.

7. The preparation method according to claim 6, characterized in that, The active material of the composite lithium-rich manganese-based cathode material was added to the organic solvent in batches.

8. A lithium-ion battery, characterized in that, The positive electrode material for lithium-ion batteries according to any one of claims 1 to 5 is used as the positive electrode material of the lithium-ion battery.