Lithium battery positive electrode material and preparation method thereof
By designing a modified binder, the problems of insufficient adhesion and poor mechanical properties of PVDF in lithium-ion battery cathodes were solved, achieving stability and safety of high-energy-density electrodes and improving the cycle life and safety of batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-11
- Publication Date
- 2026-03-13
AI Technical Summary
Existing lithium-ion battery cathode binder PVDF suffers from insufficient adhesion, poor mechanical properties, and poor thermal stability in high-load, high-pressure electrodes, leading to easy damage to the electrode structure and affecting battery cycle life and safety.
A modified binder is used, which introduces cyano groups and flexible segments of polydimethylsiloxane, and combines the cross-linking reaction of maleic anhydride and p-phenylenediamine to form a strong interfacial bond and a three-dimensional network structure, thereby improving the mechanical strength and electrolyte wettability of the binder and enhancing the adhesion between the active particles and the current collector.
High adhesion, toughness, excellent charge transport dynamics and thermal safety are achieved at low dosage, improving the mechanical integrity of the electrode and the cycle life and safety of the battery.
Smart Images
Figure SMS_1
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a lithium battery cathode material and its preparation method. Background Technology
[0002] With the rapid development of portable electronic devices, electric vehicles, and large-scale energy storage systems, the market is placing increasingly stringent demands on the energy density, power density, cycle life, and safety performance of lithium-ion batteries. One effective way to improve battery energy density is to increase the areal density and compaction density of the electrode active materials, while minimizing the proportion of inactive components (such as conductive agents and binders). Against this backdrop, the role of binders, as a key auxiliary material ensuring the integrity and functionality of the electrode structure, is becoming increasingly prominent. They not only need to firmly bond and fix the active material particles and conductive agents to the current collector to build a stable electron and ion transport network, but also need to withstand changes in the volume of the active material, erosion from high-potential electrolytes, and potential thermal shocks during long-term charge and discharge processes, ensuring the stable operation of the electrode and even the entire battery.
[0003] Currently, polyvinylidene fluoride (PVDF) is commonly used as a binder in the cathode of commercial lithium-ion batteries. PVDF possesses certain electrochemical stability and flexibility, but its bonding effect relies primarily on relatively weak van der Waals forces, resulting in insufficient inherent affinity for polar surfaces (such as most layered oxide cathode materials) and limited intramolecular cohesion. This defect is particularly prominent in high-load, high-pressure electrodes: when reducing the amount of PVDF to decrease the content of inactive materials, the structural integrity of the electrode is easily compromised, the contact resistance between the active material and the current collector increases, and even active material peeling may occur, severely damaging the battery's cycle life and rate performance. Furthermore, PVDF is a semi-crystalline linear polymer, and its mechanical properties make it difficult to balance strength and toughness. Under the stress generated during electrode rolling or battery cycling, the electrode is prone to brittle cracks or plastic deformation. More importantly, PVDF has a low melting point (about 160°C), moderate thermal stability, and exhibits some swelling in carbonate electrolytes. These factors may exacerbate the risk of interfacial side reactions and thermal runaway in batteries under harsh conditions such as high voltage and high temperature.
[0004] In recent years, researchers have been dedicated to developing novel cathode binders to overcome the performance limitations of PVDF. However, many reported binder systems often focus only on optimizing a single property, or their design strategies lack universality, making it difficult to simultaneously meet the multiple synergistic requirements of high-energy-density electrodes for binders, such as "low dosage, high adhesion, strong toughness, excellent interface, and high thermal stability." For example, while some highly polar polymers can provide high adhesion, their rigid chain segments may lead to decreased electrode flexibility and processing difficulties; while some flexible polymers may lack in mechanical strength and thermal stability.
[0005] Therefore, developing a novel high-performance cathode binder that can achieve a balance and synergy of multiple properties at the molecular level, while still ensuring excellent mechanical integrity, efficient charge transport kinetics, stable electrode / electrolyte interface, and improved thermal safety at a low dosage, is of vital importance for promoting the development of next-generation high-energy-density and high-safety lithium-ion batteries. Summary of the Invention
[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0007] This invention provides a lithium battery cathode material, characterized in that it comprises functional components and a solvent, wherein the functional components include a cathode active material, a modified binder, and a conductive agent, and the modified binder accounts for 0.3-2% of the mass content of the functional components.
[0008] Furthermore, the positive electrode active material is selected from one or more of the group consisting of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, and lithium nickel cobalt oxide.
[0009] Furthermore, the conductive agent includes one or more of conductive graphite, conductive carbon black, acetylene black, carbon nanotubes, and graphene, and the conductive agent accounts for 2-5% of the mass content of the functional components.
[0010] Furthermore, the solvent is N-methylpyrrolidone.
[0011] Further, the modified binder preparation method includes the following steps: S1, under nitrogen protection, acrylonitrile, monovinyl-terminated polydimethylsiloxane and maleic anhydride are added to DMF solvent and stirred to form a mixture, the temperature is raised to 75°C, and an initiator is added dropwise to the mixture while stirring to initiate polymerization for 30 minutes, followed by constant temperature reaction for 4 hours;
[0012] S2. Cool the system to 5°C, add the DMF solution of p-phenylenediamine dropwise while stirring, and condense at a constant temperature for 2 hours. Wash the obtained precipitate twice with deionized water and twice with ethanol, and then dry it in an oven to finally obtain the modified binder.
[0013] Furthermore, in step S1, the molar ratio of acrylonitrile, monovinyl-terminated polydimethylsiloxane, and maleic anhydride is 100:20:3-5.
[0014] Preferably, the weight-average molecular weight of the adhesive is 1-2 million.
[0015] If the content of maleic anhydride in the modified binder is too low, the cross-linking network will be sparse, resulting in insufficient mechanical strength and adhesion, which will not be able to adequately protect the electrode. At the same time, the increase in free volume will be limited, and the improvement on ion transport will not be significant. If the content is too high, an overly dense cross-linking network will be formed, and the molecular chains will be "tightened", which will lead to a decrease in free volume and a contraction in the interchain spacing. This will narrow the ion transport channel, reduce the kinetic performance, and thus impair the rate performance.
[0016] Furthermore, in step S1, the number-average molecular weight of the monovinyl-terminated polydimethylsiloxane is 500-2000 g / mol.
[0017] Furthermore, the initiator in step S1 is azobisisobutyronitrile, and the amount of initiator used is 1%-3% of the total weight of each component in step S1.
[0018] Furthermore, the molar ratio of p-phenylenediamine used in step S2 to maleic anhydride used in step S1 is 1:2.
[0019] Furthermore, the viscosity of the positive electrode slurry is 5000-15000 mPa·s, preferably 7000-8000 mPa·s.
[0020] The present invention also provides a method for preparing a lithium battery cathode material, which specifically includes the following steps: mixing a cathode active material, a conductive agent and a modified binder evenly, and then adding a solvent to adjust the viscosity to form the lithium battery cathode material.
[0021] The present invention also provides a positive electrode, the positive electrode comprising a current collector foil and a positive electrode active layer disposed on the surface of the current collector foil.
[0022] Furthermore, the positive electrode is prepared by the following method: coating the above-mentioned lithium battery positive electrode material onto the surface of the current collector foil and drying it to obtain the positive electrode.
[0023] Furthermore, the positive electrode slurry is sieved before coating.
[0024] Compared with the prior art, the present invention has the following beneficial effects:
[0025] This invention introduces cyano groups and flexible polydimethylsiloxane segments into a modified binder. The cyano groups have a strong adsorption force on the surface of oxygen-rich, polar layered oxide cathode materials (such as LiCoO2). Especially under low binder dosage conditions, this strong interaction ensures that a tight and firm interfacial bond can be formed between the binder and the active particles. The flexible polydimethylsiloxane segments can effectively absorb and dissipate the micro-mechanical stress generated by the volume change of the active material particles during lithium insertion and extraction, alleviate grain boundary strain, thereby preventing the generation and propagation of microcracks. At the same time, it can also improve electrolyte wettability and promote ion transport. In addition, maleic anhydride monomers are introduced for copolymerization during the preparation of the binder, and then p-phenylenediamine is used as a crosslinking agent. The anhydride group of maleic anhydride and the amino group of p-phenylenediamine undergo a condensation reaction to further establish a three-dimensional network structure. The crosslinking density is controlled by adjusting the amount of maleic anhydride, which significantly improves the storage modulus and mechanical strength of the binder, further inhibits the cracking and structural crushing of active material particles. The crosslinking network provides more physical bonding points, and in synergy with the polar cyano groups, it firmly "anchors" itself to the surface of active particles through strong hydrogen bonding, which greatly enhances the adhesion between the binder and the active particles and current collectors. Detailed Implementation
[0026] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.
[0027] Example 1
[0028] This embodiment provides a lithium battery cathode material, including a functional component and N-methylpyrrolidone, wherein the functional component includes LiNi with a mass content of 98%. 0.8 Co 0.1 Mn 0.1 O2 (NCM811), 0.7% by mass of modified binder and 1.3% by mass of conductive carbon black.
[0029] The modified binder preparation method described herein includes the following steps: S1, under nitrogen protection, 1 mol acrylonitrile, 0.2 mol monovinyl-terminated polydimethylsiloxane (number average molecular weight of approximately 1000 g / mol) and 0.05 mol maleic anhydride are added to 500 mL of LDMF solvent and stirred to form a mixture. The mixture is heated to 75°C, and while stirring, 1% of the total weight of the components in step S1, azobisisobutyronitrile, is added dropwise to the mixture to initiate polymerization for 30 minutes, followed by a constant temperature reaction for 4 hours.
[0030] S2. Cool the system to 5°C, and add 0.025 mol of p-phenylenediamine DMF solution dropwise while stirring. The condensation reaction is carried out at a constant temperature for 2 hours. The precipitated product is washed twice with deionized water and twice with ethanol, and then dried in an oven to finally obtain the modified binder. The weight average molecular weight of the binder is about 1.5 million.
[0031] The positive electrode in this embodiment was prepared by the following method: a specified amount of LiNi was used... 0.8 Co 0.1 Mn 0.1 O2 (NCM811), modified binder and conductive carbon black were mixed evenly, and a certain amount of N-methylpyrrolidone was gradually added and stirred at high speed. The initial viscosity of the positive electrode slurry was adjusted to about 8000 mPa·s using a Borlefeld rotational viscometer.
[0032] Example 2
[0033] This embodiment provides a lithium battery cathode material and its preparation method. The difference from Embodiment 1 is that in the preparation process of the modified binder, the molar amounts of acrylonitrile, monovinyl-terminated polydimethylsiloxane and maleic anhydride in step S1 are 1 mol: 0.2 mol: 0.03 mol, respectively. The other components, preparation steps and parameters are the same.
[0034] Example 3
[0035] This embodiment provides a lithium battery cathode material and its preparation method. The difference from Embodiment 1 is that in the preparation process of the modified binder, the molar amounts of acrylonitrile, monovinyl-terminated polydimethylsiloxane and maleic anhydride in step S1 are 1 mol: 0.2 mol: 0.04 mol, respectively. The other components, preparation steps and parameters are the same.
[0036] Comparative Example 1
[0037] This comparative example provides a lithium battery cathode material and its preparation method. The difference from Example 1 is that in the preparation process of the modified binder, the molar amounts of acrylonitrile, monovinyl-terminated polydimethylsiloxane and maleic anhydride in step S1 are 1 mol: 0.2 mol: 0.02 mol, respectively.
[0038] Comparative Example 2
[0039] This comparative example provides a lithium battery cathode material and its preparation method. The difference from Example 1 is that in the preparation process of the modified binder, the molar amounts of acrylonitrile, monovinyl-terminated polydimethylsiloxane and maleic anhydride in step S1 are 1 mol: 0.2 mol: 0.06 mol, respectively.
[0040] Comparative Example 3
[0041] This comparative example provides a lithium battery cathode material and its preparation method. The difference from Example 1 is that in the preparation process of the modified binder, the molar amounts of acrylonitrile, monovinyl-terminated polydimethylsiloxane and maleic anhydride in step S1 are 1 mol: 0.2 mol: 0 mol, respectively.
[0042] Comparative Example 4
[0043] This comparative example provides a lithium battery cathode material and its preparation method. The difference from Example 1 is that in the preparation process of the modified binder, the molar amounts of acrylonitrile, monovinyl-terminated polydimethylsiloxane and maleic anhydride in step S1 are 1 mol: 0 mol: 0.05 mol, respectively.
[0044] The positive electrode materials prepared in the above-described examples and comparative examples were coated onto the surface of aluminum foil and dried to obtain the positive electrode.
[0045] Lithium-ion secondary battery performance testing:
[0046] (1) Preparation of lithium-ion secondary batteries:
[0047] In a dry glove box under an argon atmosphere, lithium-ion coin cells (CR2032 type) were assembled using the positive electrode, negative electrode (lithium metal foil), separator (Celgard 2400), and commercial electrolyte (1 mol / L LiPF6 dissolved in ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC), EC / DMC / EMC = 1 / 1 / 1 volume ratio) prepared in the embodiments and comparative examples of the present invention.
[0048] (2) The above lithium-ion batteries were subjected to the following performance tests.
[0049] Charge / discharge specific capacity:
[0050] The battery is set to a charging state, i.e., lithium is removed from the working electrode, with a charging current density of 0.1 mA / cm². 2 The system stops operating once the charge reaches the cutoff voltage of 4.3V. Calculate the specific capacity of the first charge.
[0051] Initial delithiation specific capacity (mAh / g) = Initial delithiation capacity / Mass of active material
[0052] After the initial delithiation is complete, the battery is then set to a discharge state, i.e., lithium insertion at the working electrode, with a discharge current density of 0.1 mA / cm². 2 The discharge ends when the voltage drops to the cutoff voltage of 2.5V. Calculate the specific capacity of the first discharge.
[0053] Initial lithium insertion capacity (mAh / g) = Initial lithium insertion capacity / Mass of active material
[0054] Cyclic performance:
[0055] The battery is charged with a constant current of 0.1mA until the cutoff voltage is reached. Similarly, the battery is discharged with a constant current of 0.1mA until the cutoff voltage is reached. After resting for 10 minutes, the above steps are repeated to perform continuous charge and discharge tests. The battery capacity after 500 cycles is obtained, and the discharge capacity retention rate of the battery after 500 cycles is calculated.
[0056] Discharge capacity retention rate = (Discharge capacity after 500 cycles / Initial discharge capacity) × 100%
[0057] Table 1 Performance Test Results
[0058]
[0059] As shown in Table 1, the modified binder described in this invention significantly improves the electrochemical performance of high-energy-density cathode materials by synergistically designing the strong polarity of cyano groups, the flexible segments of polydimethylsiloxane, and the crosslinking network. With an optimized maleic anhydride molar ratio of 0.03-0.05, the cathode exhibits excellent initial coulombic efficiency and superior long-term cycling stability (capacity retention of 88.9% after 500 cycles). This indicates that at this ratio, the binder achieves an optimal balance between strong interfacial adhesion, stress buffering, and efficient ion transport. If the crosslinking is too low, the binder's mechanical strength and network support are insufficient, leading to a significant decrease in initial charge-discharge efficiency and cycle retention, failing to effectively maintain the electrode structure. An overly dense network restricts segment movement and ion transport channels, resulting in severe initial capacity loss and rapidly deteriorating cycling performance, confirming the inference that excessive crosslinking damages kinetic performance. Without the addition of maleic anhydride, the binder lacks three-dimensional network reinforcement, has low cohesive strength, and the electrode structure is easily damaged during cycling, resulting in the lowest cycle retention. Without the addition of polydimethylsiloxane, volumetric stress cannot be effectively buffered, resulting in severe damage to the material structure, manifested as extremely low initial efficiency and poor cycle stability.
[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any indirect modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.
Claims
1. A lithium battery cathode material, characterized in that, It includes functional components and solvents, wherein the functional components include positive electrode active material, modified binder and conductive agent, and the modified binder accounts for 0.3-2% of the mass content of the functional components.
2. The lithium battery cathode material according to claim 1, characterized in that, The positive electrode active material is selected from one or more of the group consisting of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium nickel cobalt oxide.
3. The lithium battery cathode material according to claim 1, characterized in that, The conductive agent includes one or more of conductive graphite, conductive carbon black, acetylene black, carbon nanotubes, and graphene, and the conductive agent accounts for 2-5% of the mass content of the functional component.
4. The lithium battery cathode material according to claim 1, characterized in that, The solvent is N-methylpyrrolidone.
5. The lithium battery cathode material according to claim 1, characterized in that, The modified adhesive preparation method includes the following steps: S1, under nitrogen protection, acrylonitrile, monovinyl-terminated polydimethylsiloxane, and maleic anhydride are added to DMF solvent and stirred to form a mixture. The mixture is heated to 75°C, and an initiator is added dropwise to the mixture while stirring to initiate polymerization for 30 minutes, followed by a constant temperature reaction for 4 hours; the initiator is azobisisobutyronitrile, and the amount of initiator is 1%-3% of the total weight of each component in step S1. S2. Cool the system to 5°C, add the DMF solution of p-phenylenediamine dropwise while stirring, and condense at a constant temperature for 2 hours. Wash the obtained precipitate twice with deionized water and twice with ethanol, and then dry it in an oven to finally obtain the modified binder.
6. The lithium battery cathode material according to claim 5, characterized in that, In step S1, the molar ratio of acrylonitrile, monovinyl-terminated polydimethylsiloxane, and maleic anhydride is 100:20:3-5.
7. The lithium battery cathode material according to claim 5, characterized in that, In step S1, the number-average molecular weight of the monovinyl-terminated polydimethylsiloxane is 500-2000 g / mol.
8. A method for preparing a lithium battery cathode material as described in any one of claims 1-7, characterized in that, Specifically, the process includes the following steps: mixing the positive electrode active material, conductive agent, and modified binder evenly, and then adding a solvent to adjust the viscosity to form the lithium battery positive electrode material.