RCinFLA
Solar Wizard
- Joined
- Jun 21, 2020
- Messages
- 3,544
A very critical process step in the fabrication of lithum Ion chemistry batteries, including LiFePO4 battery, is the initial formation of the Solid Electrolyte Interface (SEI) layer. It is crucial in protecting electrolyte from chemical decomposition facilitating long cycle life of battery. It was not originally recognized as a important part when LiIon batteries were first being developed. It is still not fully understood.
The formation process is done on a completed cell assembly. It is the first charging sequence that must be carefully done to ensure the optimum growth of the protective SEI layer with minimal damage to electrolyte layer, and minimal consumption of available Lithium. It begins with a low voltage charge starting at about 0.25v and cycles through several incremental steps of increasing voltage and current to reach its final state. Heating of cell is also used to accelerate the process. This process can take up to a couple weeks to complete. Cell impedance is measured to determine the progression of the SEI layer growth. Charging for SEI growth process is done by manufacturer and is not significantly modifiable by end user when battery is received by customer. The layer is a chemical transformation that is created between the graphite anode (negative side of battery) and the electrolyte interface. It consumes about 5% of the cell's available Lithium and thus reduces the cell's capacity.
Some continued growth of the SEI layer will occur during normal end user cycling of battery. Its continued growth consumes more of the Lithum reducing cell capacity and its increased growth thickness is an additional obsticle to the transfer of Lithium Ions increasing the impedance of cell over time.
This initial growth process is done in multi-cell batches and is one of the criteria in selecting matched cells for multi-cell battery construction. Because it is so process dependent, different batches cannot assure identical results. Because it consumes Lithium, and the amount of Lithium in a cell determines its capacity, it is important to matching capacity between cells. It also impacts cycle life degradation progression which should be closely matched for optimum longevity of multiple cell battery packs.
It is a very time consuming process in the fabration of LiIon batteries and therefore an expensive process step. A lot of work has been put into reducing the time and preciseness required of this process. Additives (manufacturers' special sauce recipes) have been put into electrolyte that are intended to help facilitate the formation of SEI layer, reduce the time required, and reduce the amount of Lithum consumed to get more useable capacity from cell. As in the case of medications, electrolyte additives side-effects may not always be fully understood.
The solid state battery, or 'silicon' battery under development has the promise of storing up to five times more ions then present graphite layer and hopefully reduce, or eliminate, the complexity of SEI layer formation.
The formation process is done on a completed cell assembly. It is the first charging sequence that must be carefully done to ensure the optimum growth of the protective SEI layer with minimal damage to electrolyte layer, and minimal consumption of available Lithium. It begins with a low voltage charge starting at about 0.25v and cycles through several incremental steps of increasing voltage and current to reach its final state. Heating of cell is also used to accelerate the process. This process can take up to a couple weeks to complete. Cell impedance is measured to determine the progression of the SEI layer growth. Charging for SEI growth process is done by manufacturer and is not significantly modifiable by end user when battery is received by customer. The layer is a chemical transformation that is created between the graphite anode (negative side of battery) and the electrolyte interface. It consumes about 5% of the cell's available Lithium and thus reduces the cell's capacity.
Some continued growth of the SEI layer will occur during normal end user cycling of battery. Its continued growth consumes more of the Lithum reducing cell capacity and its increased growth thickness is an additional obsticle to the transfer of Lithium Ions increasing the impedance of cell over time.
This initial growth process is done in multi-cell batches and is one of the criteria in selecting matched cells for multi-cell battery construction. Because it is so process dependent, different batches cannot assure identical results. Because it consumes Lithium, and the amount of Lithium in a cell determines its capacity, it is important to matching capacity between cells. It also impacts cycle life degradation progression which should be closely matched for optimum longevity of multiple cell battery packs.
It is a very time consuming process in the fabration of LiIon batteries and therefore an expensive process step. A lot of work has been put into reducing the time and preciseness required of this process. Additives (manufacturers' special sauce recipes) have been put into electrolyte that are intended to help facilitate the formation of SEI layer, reduce the time required, and reduce the amount of Lithum consumed to get more useable capacity from cell. As in the case of medications, electrolyte additives side-effects may not always be fully understood.
The solid state battery, or 'silicon' battery under development has the promise of storing up to five times more ions then present graphite layer and hopefully reduce, or eliminate, the complexity of SEI layer formation.