Modified material for lithium-rich manganese-based positive electrode of lithium ion battery

Abstract

The invention relates to the technical field of positive electrode materials of lithium ion batteries, in particular to a modified material for a lithium-rich manganese-based positive electrode of a lithium ion battery, the modified material comprises a composite binder suitable for a positive electrode material with the chemical formula of Li1. 2Ni0. 13Co0. 13Mn0. 54O2, and a complexing agent for preparing a hydroxide precursor; the composite binder is prepared from humic acid, carboxymethyl guar gum and carboxymethyl chitosan; according to the modified material for the lithium-rich manganese-based positive electrode of the lithium ion battery, the complexing agent is creatively used for preparing the hydroxide precursor, so that the positive electrode material with good structural compactness can be obtained; meanwhile, due to the arranged composite binder, relatively high mechanical properties can be obtained among particles of the positive electrode material, a three-dimensional conductive binder network is formed, good structural stability is obtained, and meanwhile, good first cycle specific capacity and capacity retention rate are further obtained; and the electrochemical performance of the lithium-rich manganese-based positive electrode of the lithium ion battery can be improved and maintained on the whole.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery positive electrode materials, and in particular to a modified material for a lithium-manganese-rich positive electrode of a lithium ion battery. Background Art

[0002] Lithium-ion batteries are widely used in electronic products, electric vehicles and other fields. With the development of the new energy industry, the performance requirements of lithium-ion batteries are increasing, and the positive electrode material is the key to improving the performance of lithium-ion batteries.

[0003] Lithium-rich manganese-based positive electrode material is one of the lithium-ion battery materials with high energy density and excellent electrochemical properties. However, during the charge and discharge process, there is a defect that the multi-component alternating stacking structure is easy to collapse due to factors such as volume expansion. This defect causes poor structural stability during the cycle, which in turn leads to poor capacity cycle retention during the cycle. This problem seriously affects the commercial value of lithium-rich manganese-based positive electrode materials. At present, in order to improve the service life of positive electrode materials, most of them adopt a coating modification process to form a coating structure on the surface of the positive electrode material. Its main function is to slow down the damage caused by the erosion of the material structure by the side reaction product HF generated by the battery during the charge and discharge cycle. However, the structural stability of the positive electrode material itself has not been effectively improved and improved. Therefore, it is considered to improve the structural stability of the lithium-rich manganese-based positive electrode material itself to maintain stable performance during the cycle. In view of this, we propose a modified material for lithium-rich manganese-based positive electrode of lithium-ion batteries. Summary of the invention

[0004] The purpose of the present invention is to solve the deficiencies mentioned in the above background technology and provide a modified material for lithium-rich manganese-based positive electrode of lithium-ion batteries.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: A modified material for a lithium-ion battery lithium-manganese-rich positive electrode, the modified material comprising a 1.2 Ni 0.13 Co 0.13 Mn 0.54 Composite binders for O2 cathode materials, and complexing agents for preparing hydroxide precursors; The composite binder comprises humic acid, carboxymethyl guar gum and carboxymethyl chitosan.

[0006] Preferably, the composite binder accounts for 2-6% of the mass of the positive electrode material.

[0007] Preferably, the mass ratio of the humic acid, carboxymethyl guar gum and carboxymethyl chitosan is 1:1:2-3.

[0008] Preferably, the complexing agent is one of sodium tartrate, ammonia water, sodium lactate and citric acid.

[0009] Preferably, the complexing agent is set to 0.2-1 mol / L.

[0010] Preferably, the preparation steps of the hydroxide precursor are specifically as follows: Step 1: Weigh nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate in a molar ratio of 1:1:4 as component raw materials, and prepare a 2 mol / L mixed metal salt solution for standby use; Step 2: setting the reaction temperature to 50-55°C and the stirring speed to 700-900r / min; adding a complexing agent to the standby mixed metal salt solution, and adding sodium hydroxide solution to adjust the pH value to 10-10.5; Step 3: After the complexing agent solution is added dropwise, the stirring speed is reduced to 150-200 r / min, and the slurry is obtained after treating for 10-14 hours; Step 4: washing the slurry in step 4 with deionized water at 50-60° C., filtering and drying in a vacuum oven at 100-120° C. to obtain a hydroxide precursor; Step 5: Using a solid-phase sintering method, weigh the hydroxide precursor and lithium hydroxide, mix them evenly, place them in a muffle furnace for calcination, and then naturally cool them to room temperature to obtain a positive electrode material.

[0011] Preferably, the step of modifying the positive electrode material with the composite binder is specifically as follows: Step 1: Evenly mix the positive electrode material, conductive carbon black and composite binder, wherein the mass ratio of the positive electrode material to the conductive carbon black is 8:1; Step 2: Add deionized water and grind and mix thoroughly for 30 minutes to obtain a uniform slurry, and use a 200um specification applicator to coat the slurry on aluminum foil; Step 3: Dry in a vacuum drying oven at 60-80°C for 12-16 hours, and cut to obtain electrode sheets.

[0012] Preferably, the complexing agent droplet acceleration rate in step 2 is set to 1-3 ml / min.

[0013] Preferably, the calcination parameters in step five are as follows: heating to 500-550°C at a rate of 6-8°C / min, keeping warm for 4-6 hours, and then heating to 850-950°C at a rate of 4-6°C / min, keeping warm for 10-12 hours.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The modified material for the lithium-manganese-rich positive electrode of a lithium-ion battery creatively uses a complexing agent to prepare a hydroxide precursor, which is beneficial to obtaining a positive electrode material with good structural density. At the same time, the composite binder provided can enable the positive electrode material particles to obtain higher mechanical properties and form a three-dimensional conductive binder network, thereby obtaining good structural stability and further obtaining good first cycle specific capacity and capacity retention rate. Overall, it is beneficial to improving and maintaining the electrochemical properties of the lithium-manganese-rich positive electrode of the lithium-ion battery. DETAILED DESCRIPTION

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0016] The present invention describes the above technical solution in detail through the following embodiments:

[0017] Embodiment 1: A modified material for a lithium-ion battery lithium-manganese-rich positive electrode, characterized in that: the modified material includes a chemical formula of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 Composite binders for O2 cathode materials, and complexing agents for preparing hydroxide precursors; Specifically, this embodiment uses humic acid, carboxymethyl guar gum and carboxymethyl chitosan in a mass ratio of 1:1:2, and limits the amount of the composite binder to 5% of the mass of the positive electrode material. The carboxymethyl chitosan and humic acid in this embodiment are purchased from Aladdin Reagent with analytical grade specifications, and the carboxymethyl guar gum is purchased from Sinopharm Group with USP specifications. At the same time, the complexing agent in this embodiment uses 0.75 mol / L sodium tartrate with analytical grade specifications sold by Sinopharm Group.

[0018] It should be explained that, in the process of preparing positive electrode materials, most commonly used binders are polyvinylidene fluoride PVDF, the purpose of which is to maintain cycle performance, but it is easy to react with conductive carbon black or lithium metal to form unsaturated bonds during use, which is easy to show as electrode material peeling, and it is easy to expand and destroy the structure and affect the structural performance, which leads to a high charge and discharge cycle attenuation rate; in this embodiment, the carboxymethyl chitosan of the composite binder is considered to be a double helix structure, which can form a good mechanical interlocking effect, that is, to obtain higher mechanical properties between the positive electrode material particles, so that it can be stably attached to the current collector to avoid peeling; humic acid contains conjugated π bonds and a large number of polar functional groups, which can form a three-dimensional conductive binder network between the positive electrode material and the conductive agent with carboxymethyl chitosan, which is beneficial to improve the conductive cycle performance and mechanical properties of the electrode; there are a large number of exposed hydroxyl groups on the surface of carboxymethyl guar gum, which can cross-link with carboxymethyl chitosan to produce a large adhesive force, and then cooperate with the three-dimensional conductive binder network to maintain good structural stability; on the whole, the purpose of the mutual cooperation of the composite binders is to make the structure more stable, not easy to peel off and have better electrochemical performance.

[0019] The complexing agent and the composite binder are not used synchronously as modifying materials, and they are applied to different stages of the preparation of the positive electrode material. Specifically, the preparation steps of the hydroxide precursor are as follows: first, nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate of analytical grade sold by Shanghai McLean Biochemical Technology Co., Ltd. are weighed in a molar ratio of 1:1:4, and configured into a 2 mol / L mixed metal salt solution for standby use; the reaction temperature is set to 55°C, the stirring speed is 800r / min, and the complexing agent is added dropwise to the standby mixed metal salt solution. In this embodiment, the control of the complexing agent dropping rate is set to 2ml / min; and sodium hydroxide solution is added dropwise to adjust the pH value to stabilize at 10.5; the addition is complete After the complexing agent, the stirring speed is reduced to 200r / min, and the slurry is obtained after treatment for 12h; the slurry is washed with 60℃ deionized water, filtered and placed in a vacuum oven at 100℃ for drying to obtain a hydroxide precursor; this embodiment uses a solid phase sintering method, and 1.45 times the total amount of nickel sulfate hexahydrate and cobalt sulfate heptahydrate sold by Anhui Zesheng Technology Co., Ltd. is weighed. Battery-grade lithium hydroxide is mixed evenly with the hydroxide precursor, and placed in a muffle furnace for calcination. The calcination parameters are specifically controlled as follows: heating to 550℃ at a rate of 8℃ / min, keeping warm for 6h, continuing to heat to 950℃ at a rate of 6℃ / min, keeping warm for 12h, and then naturally cooling to room temperature to obtain the positive electrode material.

[0020] The above process steps are to synthesize the positive electrode material by coprecipitation method, in which the complexing agent sodium tartrate is creatively added. The advantage is that sodium tartrate can further improve the complexing effect of manganese ions in the preparation process of positive electrode materials, thereby reducing the problem of differential complexing ability with nickel and cobalt ions. It should be noted that because Ni 2+ 、Co2+ , Mn 2+ The large difference in the complex constants of the three will lead to different complexing effects of their complexing agents, that is, the metal ions first form metal complex ions with the complexing agent, and then release the metal ions and hydroxide to form hydroxide precipitates. The complex precipitation rates are different, which eventually leads to structural segregation, which is not conducive to obtaining a stable and excellent structural distribution; while the complex constants of sodium tartrate for the three are similar, which are 2.06, 2.1 and 2.49 respectively, which is conducive to promoting the formation of a more uniform and stable structure.

[0021] The steps of modifying the positive electrode material with a composite binder in this embodiment are specifically as follows: uniformly mixing the prepared positive electrode material, conductive carbon black and composite binder, wherein the conductive carbon black is purchased from Sinopharm Group's battery-grade Super-P product; wherein the mass ratio of the positive electrode material to the conductive carbon black is 8:1; deionized water with a material-liquid ratio of 1:0.5 is added to wet the mixture, and the mixture is fully ground and mixed for 30 minutes to obtain a uniform slurry, and the slurry is coated on an aluminum foil using a 200um specification coater; and the mixture is dried in a vacuum drying oven at 80°C for 12 hours, and the electrode sheet is obtained by cutting.

[0022] Example 2: The difference between this example and Example 1 is that the amount of the composite binder in this example remains the same, but humic acid, carboxymethyl guar gum and carboxymethyl chitosan are specifically used in a mass ratio of 1:1:3, and other conditions are the same.

[0023] Example 3: The only difference between this example and Example 1 is that the complexing agent in this example is ammonia water, and other conditions are the same.

[0024] Example 4: The only difference between this example and Example 1 is that the complexing agent in this example is sodium lactate, and other conditions are the same.

[0025] Example 5: The only difference between this example and Example 1 is that citric acid is used as the complexing agent in this example, and other conditions are the same.

[0026] Example 6: The only difference between this example and Example 1 is that the drop rate of the complexing agent in this example is set to 3 ml / min, and other conditions are the same.

[0027] Comparative Example 1: The difference between this comparative example and Example 1 is that this comparative example does not use a composite binder, but uses existing polyvinylidene fluoride PVDF instead, and other conditions are the same.

[0028] Comparative Example 2: The difference between this comparative example and Example 1 is that the amount of the composite binder in this comparative example remains the same, but humic acid, carboxymethyl guar gum and carboxymethyl chitosan are specifically used in a mass ratio of 1:1:4, and other conditions are the same.

[0029] Comparative Example 3: The difference between this comparative example and Example 1 is that the drop-adding rate of the complexing agent in this comparative example is set to 5 ml / min, and other conditions are the same.

[0030] The battery assembled in the present application is a CR2025 button battery, the electrode sheet obtained in the above embodiment and comparative example is used as the positive electrode, the metal lithium sheet is used as the counter electrode, the Celgard2500 polypropylene organic film is used as the diaphragm, and the 1 mol / L LiPF6 ethylene carbonate and diethyl carbonate solution is used as the electrolyte. The CR2025 button battery is assembled in a glove box filled with argon atmosphere, and the battery is tested after standing for 12 hours; This application uses a CT2001A blue battery test system to test the cycle performance of the assembled button battery in a constant current charge and discharge mode; the test voltage is in the range of 2.0-4.8V, and the ambient temperature is controlled to be stable at 25°C. The first cycle capacity at a rate of 0.1C and the cycle capacity after 100 cycles of charge and discharge at a rate of 0.5C are tested, and the capacity retention rate is calculated; The specific data is as follows: <![CDATA[Initial cycle specific capacity (mAh·g －1 )]]> <![CDATA[Specific capacity at 100 cycles (mAh·g －1 )]]> Capacity retention rate (%) Example 1 290.3 262.7 90.5 Example 2 288.6 262.9 91.1 Example 3 262.7 225.1 85.7 Example 4 282.3 249.6 88.4 Example 5 270.8 235.3 86.9 Example 6 291.5 261.8 89.8 Comparative Example 1 252.9. 175.3 69.3 Comparative Example 2 254.4 189.5 74.5 Comparative Example 3 279.2 221.7 79.4 According to the data in the above table, from the data of Example 1, Example 2 and Comparative Example 2, within the scope of the present application, as the mass fraction of carboxymethyl chitosan increases, that is, the corresponding humic acid and carboxymethyl guar gum decrease, the data shows that the capacity retention rate tends to be stable, but its first cycle specific capacity has a slight downward trend. Considering that its carboxymethyl chitosan can bring good mechanical properties, it is not easy to collapse during the cycle, so it is not easy to cause cycle collapse and capacity decay; however, when the comparative example 2 is abnormal, when the carboxymethyl chitosan accounts for a large proportion, it causes the problem that the first cycle specific capacity and capacity retention rate are significantly reduced. It is considered that the problem of hindering electrochemical performance may be caused by excessive use. At the same time, considering the commercial cost and comprehensive performance, the high-proportion carboxymethyl chitosan solution is not selected; Different types of complexing agents are used in Example 1 and Examples 3-5, and the sample structures are observed to find that the positive electrode material obtained in Example 1 prepared with sodium tartrate has better compactness, which is considered to be because the structure formed is more stable, so it is beneficial to alleviate the capacity attenuation problem caused by structural degradation during the cycle. At the same time, referring to the data of Example 6 and Comparative Example 3, it is found that when the dropping rate of sodium tartrate is too fast, it will also cause the attenuation of electrochemical performance. Therefore, it is considered that its dropping rate will affect the molding quality of the hydroxide precursor, and then affect the performance of the positive electrode material.

[0031] Overall, combined with the data of Comparative Example 1, it can be seen that the first cycle specific capacity and capacity retention rate of the present application are significantly improved, and the comprehensive performance of the positive electrode material modified by the composite binder and the chelating agent has outstanding progress; and its binder ratio, chelating agent type and dripping rate all have an impact on the final performance. It can be seen from the data that the chelating agent can be selected as sodium tartrate to obtain better performance.

[0032] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A modified material for a lithium-ion battery lithium-manganese-rich positive electrode, characterized in that: The modified material includes a material suitable for a chemical formula of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 Composite binders for O2 cathode materials, and complexing agents for preparing hydroxide precursors; The composite binder comprises humic acid, carboxymethyl guar gum and carboxymethyl chitosan.

2. The modified material for lithium-ion battery lithium-manganese-rich positive electrode according to claim 1, characterized in that: The composite binder accounts for 2-6% of the mass of the positive electrode material.

3. The modified material for lithium-ion battery lithium-manganese-rich positive electrode according to claim 2, characterized in that: The mass ratio of the humic acid, carboxymethyl guar gum and carboxymethyl chitosan is 1:1:2-3.

4. The modified material for lithium-ion battery lithium-manganese-rich positive electrode according to claim 1, characterized in that: The complexing agent is one of sodium tartrate, ammonia water, sodium lactate and citric acid.

5. The modified material for lithium-ion battery lithium-manganese-rich positive electrode according to claim 4, characterized in that: The complexing agent is set to 0.2-1 mol / L.

6. The modified material for lithium-ion battery lithium-manganese-rich positive electrode according to claim 5, characterized in that: The preparation steps of the hydroxide precursor are specifically as follows: Step 1: Weigh nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate in a molar ratio of 1:1:4 as component raw materials, and prepare a 2 mol / L mixed metal salt solution for standby use; Step 2: setting the reaction temperature to 50-55°C and the stirring speed to 700-900r / min; adding a complexing agent to the standby mixed metal salt solution, and adding sodium hydroxide solution to adjust the pH value to 10-10.5; Step 3: After the complexing agent solution is added dropwise, the stirring speed is reduced to 150-200 r / min, and the slurry is obtained after treating for 10-14 hours; Step 4: washing the slurry in step 4 with deionized water at 50-60° C., filtering and drying in a vacuum oven at 100-120° C. to obtain a hydroxide precursor; Step 5: Using a solid-phase sintering method, weigh the hydroxide precursor and lithium hydroxide, mix them evenly, place them in a muffle furnace for calcination, and then naturally cool them to room temperature to obtain a positive electrode material.

7. The modified material for lithium-ion battery lithium-manganese-rich positive electrode according to claim 6, characterized in that: The steps of modifying the positive electrode material with the composite binder are specifically as follows: Step 1: Evenly mix the positive electrode material, conductive carbon black and composite binder, wherein the mass ratio of the positive electrode material to the conductive carbon black is 8:1; Step 2: Add deionized water and grind and mix thoroughly for 30 minutes to obtain a uniform slurry, and use a 200um specification applicator to coat the slurry on aluminum foil; Step 3: Dry in a vacuum drying oven at 60-80°C for 12-16 hours, and cut to obtain electrode sheets.

8. The modified material for lithium-ion battery lithium-manganese-rich positive electrode according to claim 6, characterized in that: The complexing agent drop rate in step 2 is set to 1-3 ml / min.

9. The modified material for lithium-ion battery lithium-manganese-rich positive electrode according to claim 6, characterized in that: The calcination parameters in step five are as follows: heating to 500-550°C at a rate of 6-8°C / min, keeping warm for 4-6 hours, and then heating to 850-950°C at a rate of 4-6°C / min, keeping warm for 10-12 hours.