The 4680 battery is Tesla's new generation cylindrical battery with a diameter of 46mm and a height of 80mm.
P1: 4680 battery display diagram
As for the battery, the power density will decrease when the energy density increases. The diameter of 46mm is the optimal choice for the cylindrical battery with both high energy density and high power density.
P2: Changes in size and performance of cylindrical batteries
1.2. Core innovation
Large cell + full pole ear + dry cell technology
1.3. Performance breakthrough
4680 battery greatly improves the battery power (6 times of 2170 battery), reduces the battery cost (14% of 2170 battery), optimize the heat dissipation performance, production efficiency, charging speed, energy density, cycle performance has further room for improvement.
2. Structural change
2.1. Full pole ear
The 4680 battery greatly improves the battery power, optimizes the heat dissipation performance, production efficiency and charging speed by changing the pole lug structure.
2.1.1. Full pole lug construction
Electrode lug: Metal conductive material that leads the positive and negative electrodes from the cell and is the contact point for charging and discharging of the battery. In the battery work, the electron flows from the positive electrode ear to the negative electrode ear, its flow path is proportional to the battery internal resistance, flow width is inversely proportional to the battery internal resistance, and the battery internal loss power is proportional to the square of the internal resistance, so the larger the contact area of the electrode ear, the shorter the distance between the electrode ear, the higher the battery output power.
Conventional batteries have only two electrodes, one connecting the positive electrode and the negative electrode, but 4680 batteries achieve full electrode ears (directly cut from the positive electrode/negative electrode ear), thus greatly increasing the current path, and shorten the electrode ear spacing, and thus greatly improving the battery power.
2.1.2.Advantages of full pore ear
1. Improved output power: the battery current path becomes wider, and the internal resistance is greatly reduced, so the internal loss is reduced, and the battery power is greatly increased (6 times that of the 2170 battery).
2. Improve safety: cylindrical battery is different from sheet battery. Its heat dissipation is mainly axial, and the heat is scattered from the pole ear. Conventional cylindrical batteries such as 2170 have only two lugs and narrow heat transfer channels, so the heat dissipation effect is not good. The 4680 battery has a large increase in pole ear area and a wide heat transfer channel, which greatly improves the heat dissipation effect (only 20% of the traditional cylindrical battery) and enhances the thermal stability of the battery.
3, fast charging performance is greatly improved: due to the full pole ear structure, electrons are easier to move in the battery, the current ratio is improved, so the charging and discharging speed is faster.
3.Dry cell technology
Dry electrode technology can be used for both positive and negative electrodes.
3.1. Traditional wet process
The material needs to be placed in solution, then dried and pressed into film: Using solvent adhesive materials, including NMP (N-methylpyrrolidone) is one of the common solvents, and will be of adhesive solvent mixes with negative or positive electrode powder, the slurry coating on the electrode set electricity body and dry, the solvent toxic, to be recovered for purification and recycle, the intermediate need large, expensive and complex electrode coating machine.
3.2. Dry cell process
Dry electrode process completely skips the step of adding solution, can omit the complicated coating, drying and other processes, greatly simplifies the production process: the active positive and negative particles and polytetrafluoron (PTFE) mixed, make its fibrosis, directly with powder rolling into a film pressed to aluminum foil or copper foil, the preparation of positive and negative pieces.
3.3. Advantages of dry batteries
1, the process is simple, cost saving: no solvent, eliminating the expensive coating machine.
2, improve production efficiency: dry electrode technology to increase the production speed to seven times before.
3, increase the battery energy density: in the case of solvent, lithium and carbon mixed with lithium metal can not be well integrated with each other, there is a first cycle capacity loss problem, dry battery technology will greatly improve this problem, so as to improve the battery energy density. At the same time, the thickness of positive electrode material was increased from 55μm to 60μm to improve the ratio of active electrode material, and the energy density was increased by 5% while ensuring the power density.
3.4. Dry battery process difficulties
The current process is not mature, the battery should be thick, the cylinder should be rolled up, easy to crack.
4. The silicon anode
1.Higher theoretical energy density: graphite anode theory maximum battery capacity 372Wh/kg, silicon anode theory maximum battery capacity up to 4200Wh/kg.
2.Better safety: silicon voltage platform is higher than graphite, now anode graphite will produce lithium dendrite, because their voltage platform is close to the precipitation potential of lithium, branch crystal pierced diaphragm, positive and negative poles will short-circuit, serious threat to battery safety.
3.Lower cost: silicon material is widely sourced, abundant in reserves, low production cost and environmentally friendly. Lithium-ion batteries using silicon anode materials can increase their mass energy density by more than 8 percent and volume energy density by more than 10 percent, while reducing their cost per kilowatt-hour by at least 3 percent.
1. Poor cycling performance: after embedding lithium, the volume of graphite does not expand significantly after embedding lithium ions, but the volume of silicon expands more than four times after embedding lithium ions, and the battery is scrapped after several times of expansion and contraction.
2.Poor conductivity: the low conductivity of silicon limits the full use of its capacity and the rate performance of silicon electrode materials; The change of volume makes the contact between active substance and conductive binder poor, and the conductivity decreases. SEI film on silicon surface is thick and uneven, which affects the conductivity and the overall specific energy of the battery.
4.3. 4680 Battery Innovative design
Tesla's redesign of the raw material to use a highly elastic material and an ionic polymer coating that increases elasticity can stabilize the silicon surface structure and reduce costs by 5%.
P6:Tesla silicon anode process principle
4680 battery core innovation process: large cell + full pole lug + dry cell technology, enhance battery power and safety, improve production efficiency, fast charging performance, reduce battery cost, energy density, cycle performance has further improved space. At present, the difficulty lies in the fabrication, welding and dry electrode process of the whole electrode lug. 4680 battery was first applied in high nickel system. It is expected that Tesla and Panasonic will start mass production in the first half of 22, which will drive the demand of high nickel positive electrode + silicon carbon negative electrode + carbon nanotube conductive medium + large cylindrical structure parts + new lithium salt, and the corresponding tap will benefit. Yiwei is leading the layout of large cylindrical batteries in China, and plans to invest 20GWh capacity, which is expected to be increased in 23 years.