What Is The Difference Between Solid-State Batteries And Flow Batteries?
1. Differences in process between solid-state batteries and traditional liquid batteries
Solid-state batteries use solid electrolytes to replace the electrolyte and separator of traditional liquid batteries. Traditional liquid lithium batteries are composed of four key elements: positive electrode, negative electrode, battery electrolyte and separator. Solid-state batteries use solid electrolytes to replace the electrolyte and separator in traditional liquid batteries.
Since all-solid-state batteries use a new material system and battery structure, the existing traditional lithium battery manufacturing process and equipment cannot achieve its industrial production and manufacturing, and corresponding innovation and improvement are required. At present, all-solid-state batteries have not yet been mass-produced, so the production process has not been finalized, and the production process and manufacturing process of different types of solid-state batteries will be different, depending on the design and application of the battery. But it is certain that there are significant differences between the production process of all-solid-state batteries and the existing traditional liquid battery production process. It is mainly reflected in the following aspects:
1.1 Front-end electrode sheet production link
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Traditional lithium batteries: using wet slurry and coating technology, the active material, conductive agent and binder are mixed into slurry and then coated on the current collector, by drying and rolling.
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Solid-state battery: Introducing dry electrode technology, eliminating the use of solvents, and directly preparing electrode sheets through dry slurry and coating processes. In addition, the electrolyte membrane needs to be coated and rolled to form a solid electrolyte layer.
1.2 Mid-stage battery cell assembly link
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Traditional lithium battery: Using winding or lamination process, the positive and negative electrode sheets and diaphragms are wound into battery cells, and then the electrolyte is injected and packaged.
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Solid-state battery: The lamination process is used, combined with electrode sheet glue frame printing and isostatic pressing technology to ensure close contact between the solid electrolyte and the electrode. Since all-solid-state batteries do not require electrolytes, the injection process is omitted.
1.3 Post-stage formation and packaging link
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Traditional lithium battery: After packaging, the battery is activated by low-pressure formation.
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Solid-state battery: Due to the high ionic conductivity requirements of solid electrolytes, the formation process tends to be high-pressure to optimize battery performance.
In general, the main differences between the core production process of all-solid-state batteries and traditional liquid lithium batteries are:
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In the front-end solid electrolyte and electrode sheet production process, all-solid-state batteries are more suitable for dry electrode technology, and dry mixing and dry coating are added to realize the preparation of solid electrolyte membrane;
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In the middle-stage battery cell assembly process, solid-state batteries use "stacking + electrode sheet glue frame printing + isostatic pressing technology" to replace the traditional winding process, and delete the injection process;
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In the back-end formation and packaging process, the conversion from chemical composition to high-voltage chemical composition.
2. Solid-state battery process
2.1 Dry electrode technology is more suitable for solid-state batteries
The biggest advantage of dry electrode technology is that it can increase the compaction density of electrodes, thereby increasing battery energy density. Dry electrode technology is a new type of electrode manufacturing process, and its biggest advantage is that it can increase the compaction density of electrodes. At present, lithium batteries mainly use traditional wet electrode manufacturing technology. In the wet electrode manufacturing process, solvents are needed to mix active materials, conductive agents and binders and then coat them on the current collector, and then dry, recover NMP solvents and roll them. The dry electrode technology directly mixes the electrode materials into dry powder and mechanically presses them onto the current collector to form an electrode sheet. This method can increase the compaction density of the electrode. For solid-state batteries, a higher compaction density means that more positive and negative electrode materials can be accommodated in the same volume, thereby increasing the energy density of the battery.
Dry electrode technology is more suitable for high-energy density batteries such as solid-state batteries. The concept of dry electrode technology is similar to that of solid-state batteries. In all-solid-state batteries, sulfide electrolytes are sensitive to organic solvents, and metallic lithium easily reacts with solvents to cause expansion. The traditional PVDF-NMP system has limited bonding strength, while the two-dimensional network structure composed of PTFE (polytetrafluoroethylene) fibrillation in the dry electrode can inhibit the volume expansion of active material particles and prevent them from falling off the current collector surface.
In addition, using the dry electrode process, the electrode sheet manufacturing process of solid-state batteries can be completely dried, eliminating the problem of residual solvent molecules after drying in the wet process. Therefore, dry electrode technology is more suitable for solid-state battery production.
The dry electrode technology simplifies the process and improves efficiency, has cost advantages, and is conducive to promoting the commercialization of solid-state batteries. The dry electrode process can simplify the production process, reduce costs, and improve production efficiency. Dry electrode sheet manufacturing does not require NMP solvent, and the drying and solvent recovery links can be reduced in the electrode sheet production process. The electrode manufacturing process is integrated, and the mixing, pulping, coating, drying, rolling and other processes required by the wet process are integrated. The process flow is simpler and the equipment occupies a smaller area. According to Nanoconol's forecast, the mass production of dry electrodes can reduce battery costs by more than 10%. In addition, the simplified dry electrode technology is suitable for large-scale production of battery electrode sheets. Therefore, dry electrode technology is considered to be one of the important technologies to promote the commercialization of solid-state batteries.
The key difficulty of dry electrode technology at present: According to Nanoconol, the key difficulty of dry electrode technology at present lies in the uniformity of mixed electrode material powder and the consistency of film formation. In the field of equipment, the dry process has higher requirements for the accuracy, uniformity and compaction density of rolling.
2.2 Middle section battery cell assembly link: adopt "stacking + electrode sheet glue frame printing + isostatic pressing technology"
① Electrode stacking machine: Solid-state batteries are not suitable for winding equipment, and need to use stacking machines, and higher precision requirements.
Both solid-state batteries and liquid batteries need to use stacking machines, but because the solid electrolyte of solid-state batteries has brittle characteristics and higher requirements for equipment precision and stability, it requires more stacking processes. Therefore, the demand for stacking machines required for solid-state battery manufacturing will also increase.
② Solid-state battery electrode sheet glue frame lamination technology: Improve the fit of solid-state battery electrode sheets and avoid internal short circuit problems.
The existing solid-state battery production process is still immature and has some shortcomings. When the electrode sheet roll is compounded with other electrode sheets after the cutting process to prepare solid-state battery cells, it is difficult to ensure that adjacent electrode sheets have a high fit, which leads to a decrease in the quality of solid-state battery cells. According to the patent technology disclosed by Liyuanheng, it proposes a solid-state battery electrode sheet glue frame lamination method, device and stacking equipment, which can improve the fit between adjacent electrode sheets in solid-state battery cells and ensure the quality of solid-state battery cells.
③ Isostatic press is one of the core incremental equipment: Isostatic pressing technology is used to improve the solid-solid interface contact problem of solid-state batteries.
The production of solid-state batteries is generally to stack the positive electrode, solid electrolyte, and negative electrode together. Considering that the solid electrolyte needs to form a good solid-solid interface contact with the electrode, contact loss will occur during the cycle, and lithium dendrite formation must be suppressed, etc., new press equipment is required during stacking, and a pressure of more than 100MPa is applied to make the materials densely stacked. Traditional hot pressing and roller pressing solutions provide limited pressure and uneven pressure, which makes it difficult to ensure the consistency requirements of dense stacking, thereby affecting the performance of solid-state batteries.
Isostatic pressing technology is based on the Pascal principle. Materials such as metals, ceramics, composite materials and polymers can be densified and pores can be eliminated. For solid-state batteries, isostatic pressing technology can effectively eliminate the gaps inside the battery cell, ensure that the electrolyte material reaches the ideal degree of densification, and improve the contact effect between the interfaces of the components in the battery cell, thereby significantly improving the ion conductivity by more than 30%, reducing the internal resistivity of the battery by more than 20%, and increasing the cycle life by 40%, greatly improving the battery performance. The equipment required for isostatic pressing is an isostatic press.
Challenges currently faced by isostatic pressing technology in the field of solid-state battery manufacturing: Isostatic pressing technology itself is a mature technology and has been widely used in ceramics, powder metallurgy and other fields. However, its application in the field of solid-state batteries is still in the exploration and development stage, and the technical maturity is relatively low. At present, the promotion of isostatic pressing technology in the field of solid-state batteries still faces challenges such as how to select the appropriate pressing temperature and pressure combination, how to control the compaction surface, and how to improve production efficiency and yield.
3. Post-stage formation and packaging link: New high-voltage formation equipment
The conventional lithium battery formation pressure requirement is 3-10 tons, while the solid-state battery formation pressure requirement is increased to 60-80 tons. The core reason why solid-state batteries require high-voltage formation is their unique solid-solid interface characteristics and ion conduction mechanism, which is fundamentally different from the formation process of traditional liquid batteries.
① Solve the solid-solid interface contact problem: The solid electrolyte and the electrode are in rigid contact, with microscopic gaps and poor contact. High pressure (usually 60-100MPa) must be pressed to eliminate the interface gaps and increase the effective contact area; promote the physical/chemical combination of the solid electrolyte and the electrode.
② Activate the ion conduction channel: The solid electrolyte has low ion conductivity, and high-voltage formation is required to force lithium ions to penetrate the solid-solid interface barrier, form an ion conduction network at the interface, and reduce the interface impedance.
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