Introduction to Coin Cell Batteries

Lithium-ion button batteries are mainly composed of the following parts: positive case, negative case, (positive/negative)electrode sheet, battery separator, spacer, spring, electrolyte.

The C in the commonly used regular commercial button battery CR2032 indicates that the positive electrode is MnO2, and there are BR series, and B indicates that the positive electrode is carbon fluoride. C or B stands for the buckle system, and R stands for the shape of the battery is round. The first two digits are the diameter (in mm), the last two digits are the thickness (in 0.1 mm), whichever is closest to the two. For example, the approximate dimensions of CR2032 are 20 mm in diameter and 3.2 mm in thickness.

1.1 Battery Coin Cell Case

The picture below shows the CR2032 button cell battery case, the positive case is larger, and the negative case has a mesh structure on the surface and is smaller, so the general assembly process starts from the negative case.

1.2Electrode sheet

The preparation process of the pole piece has an important influence on whether the electrochemical performance can be fully exerted. The figure below shows the pole piece prepared by the positive electrode material.

The positive and negative current collectors of lithium-ion battery pole pieces are Aluminum Foil and copper foil respectively. If a single-sided smooth foil is selected, it is often coated on the rough surface to increase the bonding force between the current collector and the material. The thickness of the foil is not strictly required, but there are relatively high requirements for the uniformity of the surface density of the foil. Silicon-based anode materials generally use carbon-coated copper foil to improve adhesion, reduce contact resistance, increase the reproducibility of test results, and improve charge-discharge cycle performance. What kind of electrode is a good electrode? The following aspects should be met: (1) The slurry is evenly coated, no obvious uneven thickness can be observed, and even bright-colored aluminum foil can be observed in particularly thin places;(2) The pole piece is kept in a complete round shape without damage, and there are no burrs around it as much as possible; (3) There are no particles in the coating area of the pole piece and no obvious powder falling phenomenon.

1.3 battery separator

(3) The  separator used in the laboratory is generally Celgard2400 or other products of the Celgard series, which are punched into small discs and used, and the diameter is slightly larger than the positive and negative pole pieces. The separator can be selected according to the performance requirements of the battery. What is the function of the diaphragm? To put it simply, if there is no separator, the positive and negative electrodes will be in direct contact, that is, a short circuit will occur. This is why in some batteries, the generation of lithium dendrites should be suppressed to prevent them from piercing the separator and causing a local short circuit. security incident. The separator is generally made of polymer materials such as polyethylene, which is not conductive, and has many micropores in its structure, allowing lithium ions to pass through, although it is an insulator.

1.4 lithium chips (i.e. negative electrode sheet)

The diameter of the negative electrode sheet is slightly smaller than the diameter of the negative electrode shell. The diameter of the lithium sheet of CR2032 is 15.8mm. The laboratory often uses a punching die with a diameter of 14mm (corresponding to the CR2032 button battery) to punch the positive electrode sheet.

Lithium chips are relatively soft and easily deformed, so you can use the positive case (because it is relatively large) to flatten the deformed lithium sheets before installing the battery. Moreover, lithium metal is easily oxidized and deteriorated in the air, and it is easy to explode when exposed to water. Therefore, the purchased lithium metal sheet needs to be opened in the glove box. Be careful not to damage the gloves when opening.

1.5 spacer

The spacer is a circular aluminum sheet with the same diameter as the lithium sheet. In the experiment, different specifications and thicknesses can be purchased according to the needs.

Note: spacer, positive and negative electrode sheet and other components should be ultrasonically cleaned with alcohol before use, and then dried in a blast drying oven.

1.6 spring (support piece)

The spring is mainly to support the battery. If there is no shrapnel, the battery will be flattened during the battery pressing step, and the internal components may be crushed. The shrapnel is only added on the negative electrode side, but if the shrapnel is added to both the positive and negative electrodes, the buckle cannot be closed during the battery pressing step, which will cause the electrolyte to come into contact with the air, and the experiment will fail.

1.7 Electrolyte Different materials generally correspond to different electrolytes.

1.8 Material Selection: Positive and negative polar active materials are generally powder materials, and the particle size should not be too large to facilitate uniform coating. At the same time, it should avoid the limitation of material dynamic properties and the problem of electrode non-uniformity caused by large particles in the test results. The maximum particle diameter (Dmax) of positive and negative electrode materials used for laboratory research generally does not exceed 50 μ m. The Dmax of lithium battery materials for industrial applications is generally less than 30 μ m。 Large particles, aggregates, or nanoscale materials often undergo sieving or grinding treatment. Carbon based conductive agents are commonly used in lithium batteries, including conductive materials such as acetylene black (AB), conductive carbon black, Super P, and 350G. Common binder systems include polyvinylidene fluoride oil-based system [i.e. poly (vinylidene fluoride), PVDF system] and polytetrafluoroethylene water-based system [i.e. poly (fluorotetraethylene), generally lotion, PTFE system for short], SBR (styrene butadiene rubber) lotion, etc. Oil based solvents often use NMP (N-methylpyrroli).