I Introduction

1. Definition

The 4680 battery is a new generation of cylindrical batteries that are 46mm and have a height of 80mm.

4680 battery display

For the battery, when the energy density increases, the power density decreases. A diameter of 46mm is the optimal choice for cylindrical batteries to combine high energy density and high power density.

Cylindrical battery size and performance change

2. Core innovation

Large battery + Tabless + dry battery technology

3. Performance breakthrough

The 4680 battery greatly enhances battery power (6 times in 2170 batteries), reduces battery cost (14% in 2170 batteries), optimizes heat dissipation performance, production efficiency, charging speed, energy density, and relay performance.

II Structure change

1. Tabless design

The 4680 battery changes through the TAB structure, greatly improving battery power, optimizing heat dissipation performance, production efficiency, and charging speed.

1.1. Tabless structure

Tab: The metal conductor that leads from the positive and negative electrodes in the cell is the contact point when the battery is charged and discharged. In battery operation, electrons flow from the positive tab to the negative tab. The path through which they flow is proportional to the internal resistance of the battery. The width of the flow through is inversely proportional to the internal resistance of the battery, while the internal power loss of the battery is proportional to the square of the internal resistance. Therefore, the larger the tab contact area and the shorter the tab spacing, the higher the battery output power.

Usually, two tabs are connected to the positive electrode and the negative electrode, and the 4680 battery has realized Tabless (directly from the positive/negative electrode), thereby greatly increasing the current path, and shortening the tab spacing, which in turn increases the battery power.

1.2. Tabless advantage

1) Improve the output power: the battery current is widened, and the internal resistance is greatly reduced, and the internal loss is reduced, which in turn greatly enhances the battery power (6 times in 2170 batteries).

2) Improve safety: The cylindrical battery is different from the sheet battery. Its heat dissipation is axial, and the heat is scattered from Tab. Traditional cylindrical batteries such as 2170 have two tabs, the heat transfer channel is narrow, so the heat dissipation effect is not good. The 4680 battery TAB area has increased, and the heat transfer channel is wide and greatly improved (only 20% of the traditional cylindrical battery), enhancing the thermal stability of the battery.

3) The fast charge performance is greatly improved: due to the tabless structure, electrons are easier to move in the battery, and the current magnification is improved, so the charge and discharge speed are faster.

4) Improve production efficiency: Eliminate the process and time of the production line to add the tab, save equipment space, and reduce the possibility of manufacturing defects.

2. Large battery

2.1. Performance

The 4680 battery has increased in diameter and height than before. The diameter is increased from 27 mm to 46 mm, and the height is increased from 70 mm to 80mm. The thickness of the battery is increased, the curvature is lowered, and the hollow portion is greater.

2.2. Advantages

1) Reduce battery costs: reduce the proportion of the housing on unit battery capacity, the number of structural members and welding is also significantly reduced (cost reduction by 14% compared to 2170).

2) Improve power density: As battery size increases, the number of batteries in the battery pack is reduced, and the proportion of metal housing is reduced. The proportion of the positive electrode and negative electrode is increased, and the energy density is improved.

3) BMS system is more worry-free: the number of batteries in battery packs is reduced, and it is simpler for battery monitoring and status analysis.

4) Structural strength increases, combined with CTC technology: larger size, higher structural strength. As part of the structural battery, it has become part of the vehicle structure, providing energy. It also serves as a structure, saving space, also reduces weight (10%). Therefore, the endless mileage (14%) is improved.

2.3. Disadvantages

Increased heat generation: The larger the battery size, the more heat generation, the harder heat dissipation, so the heat control is more difficult. Tesla has made a breakthrough in thermal stability performance with tabless technology.

2.4. Actual performance

As the battery size is increased, the number of batteries in the battery pack is reduced, and the proportion of metal casings is reduced, the proportion of the positive pole, and the negative electrode is increased, and the energy density is improved. Compared with 2170 batteries, 4680 battery energy has increased by 5 times. The current endless mileage (16%) is mainly from CTC technology (14%). With the continuous upgrade of the material system, the battery energy density has further enhanced space.

III Dry battery technology

The dry electrode technology can be used simultaneously on the positive and negative electrodes.

1. Traditional wet process

The material needs to be placed in solution, then dried and pressed into a film: solvents with binder materials are used, of which NMP (N-methylpyrrolidone) is one of the common solvents, and the solvent with the binder is mixed with the negative or positive powder, then the paste is applied to the electrode collector and dried, where the solvent is toxic and needs to be recovered, purified and reused, requiring huge, expensive and complex electrode coating in between machines.

2. Dry battery technology

The dry electrode process thoroughly skips the addition of the solution step. It can omit the process of complicated coating, drying, and greatly simplify the production process: The active positive and negative particles are mixed with polytetrafluoroethylene (PTFE) to fibrillate them. The positive and negative electrode sheets are prepared by rolling and grinding the powder directly into a film and pressing it onto aluminum or copper foil.

3. Dry battery advantage

1) Simple process, cost savings: no solvent, save expensive coating machine.

2) Improve production efficiency: The dry electrode technology enhances the production speed to the previous seven times.

3) Increasing battery energy density: With solvents, lithium and carbon mixed with lithium metal do not fuse well with each other and have the problem of first cycle capacity loss. Dry cell technology will greatly improve this problem and thus enhance the battery energy density. Also increase the thickness of cathode material from 55μm to 60μm to enhance the active electrode material ratio, so that the energy density can be increased by 5% while ensuring the power density.

IV Silicon negative electrode

1. Advantage

1) Theoretical energy density is higher: the maximum battery capacity of graphite negative theory is 372Wh / kg, and the maximum battery capacity of silicon negative polarity can reach 4200Wh / kg.

2) Safety is better: Silicon has a higher voltage plateau than graphite. Nowadays, lithium dendrites are produced in the negative graphite because their voltage plateau is close to the precipitation potential of lithium. If the dendrites pierce the diaphragm, the positive and negative electrodes will be short-circuited, seriously threatening battery safety.

3) The cost is lower: Silicon materials are widely sourced, abundant, cheap to produce, and environmentally friendly. The mass-energy density of lithium-ion batteries with silicon cathode materials can be increased by more than 8% and the bulk energy density by more than 10%, while the cost per kWh of the battery can be reduced by at least 3%.

2. Disadvantage

1) Poor cycle performance: Graphite has no significant volume expansion after the lithium-ion is embedded. But silicon in the lithium-ion embedded volume expansion of more than four times, back and forth several expansion and contraction of the battery will be scrapped.

2) Poor conductivity: The low electrical conductivity of silicon limits the sufficient utilization of its capacity and the magnification performance of the silicon electrode material; the volume change is in contact with the conductive agent binder, the conductivity is lowered; the SEI film of the silicon surface is thick and not Uniform, affecting conductivity and battery overall than energy.

3. 4680 Battery Innovation Design

Tesla redesigned the raw material to take a highly elastic material and by adding an elastic ionomer coating, it was able to stabilize the silicon surface structure and reduce the cost by 5%.

Tesla silicon negative process principle

4. Silicon carbon negative development direction

Battery companies actively apply silicon-carbon cathode: silicon-carbon cathode is currently mainly used in cylindrical batteries, Ningde Time, Lixin Battery, Guoxuan High-tech, and Pryde and other power battery manufacturers high specific capacity battery program, silicon carbon cathode for the clear development direction.

Silicon carbon battery is the inevitable trend of high energy density development, with the technical bottleneck overcome and the end customer acceptance, silicon carbon will cost down, to achieve mass production, CNCET expects that in 23 years China's silicon-carbon anode material production and consumption will reach 60,000 tons, the future silicon-carbon anode market has great prospects.

V Positive electrode

Different electrodes are used in different products. The lithium iron version of 4680 will be used in low range models and energy-saving batteries, focusing on more cycles; the lithium nickel-manganese 4680 battery is used in medium range models and home batteries; the high nickel 4680 battery is used in cybertruck and Semi.

Tesla cathode materials mainly in the direction of high nickel cobalt-free, but did not propose an innovation outside the mainstream route: the use of NCA single crystal route to enhance energy density by increasing the voltage, the thermal stability of the material comparable to lithium iron phosphate.

The trend of 4680 battery positive electrode

4680 battery actually has three different positive electrode materials: ferrets, nickel manganese, high nickel.

1) 4680 battery is currently mainly based on high nickel

The 4680 high-tight nickel version is currently the main direction in Tesla, and in the future, in the high-declarable Cyber Truck and SEMI, long-lasting and high-performance version of Model 3 and Model Y can also be used.

2) 4680 battery nickel manganese version will keep up with high nickel version

After the 4680 high-nickel is mature, 4680 nickel-manganese will be developed, which will be applied to a medium-end battery model, Model Y and household batteries.

3) 4680 Battery will also use iron lithium positive

4680 battery also uses iron lithium positive: Tesla battery conference, did not mention its cycle performance, because silicon-based anode volume expansion reduced charge and discharge, after the nickel manganese version of 4680 battery technology, the lithium version of 4680 battery A large probability is also available, applied to low-cost models, energy savings batteries, main high cycle performance.

VI Conclusion

4680 battery core innovation process is large cell + tabless + dry cell technology. 4680 battery enhanced battery power and safety, improved production efficiency, fast charging performance; reduce the cost of the battery; energy density, cycle performance has further room for improvement. The current technical difficulties lie in the production and welding of the full pole lug, dry electrode process. 4680 battery is the first to be applied to high nickel system, is expected to the first half of 22 years Tesla and Panasonic began mass production, will drive high nickel cathode + silicon-carbon cathode + carbon nanotubes conductive agent + large cylindrical structural components + new lithium salt demand.