During the use of
lithium-ion batteries, the actual usable capacity will continue to decrease relative to the rated capacity at the time of delivery. Any side reaction that can consume lithium ions may cause a change in the balance of lithium ions in the battery. This change in the balance state is irreversible and can be accumulated through multiple cycles, thereby adversely affecting battery performance.
A charge and discharge of a battery is called a cycle, and the cycle life is an important indicator of battery life performance. The fundamental reason behind the factors that affect the cycle life of lithium-ion batteries is that the number of lithium ions involved in energy transfer is constantly decreasing. The total amount of lithium in the battery has not been reduced, but the "activated" lithium ions are less, they are imprisoned in some places or the transmission channel is blocked, and they cannot freely participate in the process of charging and discharging. Specifically:
(1) The precipitation of metallic lithium: generally occurs on the surface of the negative electrode. When the lithium ions migrate to the negative electrode surface, some of the lithium ions do not enter the negative electrode active material to form a stable compound. Instead, they obtain electrons and deposit on the negative electrode surface to become metallic lithium, and No longer participate in the subsequent cycle process, resulting in a decrease in capacity. For example, when the negative electrode material is insufficient or overcharged, the negative electrode cannot accommodate the lithium ions migrated from the positive electrode, resulting in the deposition of metal lithium; during high-rate charging, the excessive amount of lithium ions reaching the negative electrode in a short period of time causes channel blockage and Precipitate out.
(2) Decomposition of cathode material: The lithium-containing metal oxide of the positive electrode material will continue to decompose during long-term use, producing some electrochemical inert substances and some flammable gases, destroying the capacity balance between the electrodes and causing irreversible loss of capacity.
(3) SEI film on the electrode surface: For carbon anode materials, during the initial cycle, the electrolyte will form a solid electrolyte (SEI) film on the surface of the electrode. The formation process of the SEI film will consume lithium ions, and the SEI film is not stable and will be in the cycle process. The continuous rupture of the battery will expose the new negative electrode surface and then react with the electrolyte to form a new SEI film, which will continue to cause the continuous loss of lithium ions and electrolyte, resulting in a decrease in the capacity of the battery. In addition, SEI film Lithium ion diffusion channels may be blocked, which will also cause a decrease in battery capacity.
(4) Loss of electrolyte: In the process of continuous circulation, the electrolyte will continue to decompose and volatilize, resulting in a decrease in the total amount of electrolyte, inability to fully infiltrate the positive and negative materials, and incomplete charge and discharge reactions, resulting in a decrease in the actual use capacity. In addition, if the electrolyte contains a certain amount of water, the water will chemically react with LiFP6 to produce LiF and HF. HF then destroys the SEI film and generates more LiF, causing LiF deposition and continuous consumption of active lithium ions. Cause the battery cycle life to decrease.
(5) The diaphragm is blocked or damaged: During the cycle of lithium-ion batteries, the gradual drying up of the diaphragm and failure is also a cause of capacity decline. Due to the drying up of the isolation membrane, the ohmic internal resistance of the battery increases, causing blockage of the charging and discharging channels, incomplete charging and discharging, and the battery capacity cannot be restored to the initial state, which greatly reduces the capacity and service life of the battery.
(6) The positive and negative electrode materials fall off: The active materials of the positive and negative electrodes are fixed on the substrate by the binder. During long-term use, due to the failure of the binder and the mechanical vibration of the battery, the active materials of the positive and negative electrodes continuously fall off and enter the electrolyte solution. , Which leads to the continuous reduction of active materials that can participate in the electrochemical reaction, and the continuous decrease of the cycle life of the battery. The long-term stability of the binder and the good mechanical properties of the battery will be able to delay the decline in the cycle life of the battery.
The current test methods used to evaluate the life of lithium-ion batteries generally undergo continuous charging and discharging cycle tests, which require a long test cycle. Lithium-ion battery standards generally specify cycle life requirements and test methods. In the existing domestic lithium-ion battery standards, the test requirements for the cycle life of lithium-ion batteries are shown in Table 1.
|
Standard
|
Use field
|
Test
current
|
Minimum
life requirement
|
|
GB/T 18287-203
|
cell phone
|
1C5
|
300 times
|
60% capacity
|
|
MT/T 1051-2007
|
Miner's
lamp
|
1C5
|
300 times
|
60% capacity
|
|
GJB 4477-2002
|
-
|
0.2C5
|
400 times
|
70% capacity
|
|
GB/T 36972-2018
|
electric
bicycle
|
0.5C5
|
600 times
|
70% capacity
|
|
GB/T 31484-2015
|
electric
car
|
1C1
|
500 times 1000 times
|
90% capacity 80% capacity
|
|
CEC 171-2018Energy type
|
Power
storage
|
nx Pn constant power
|
1000 times 2000 times
|
90% energy 80% energy
|
|
CEC 171-2018Power type
|
Power
storage
|
nx Pn constant power
|
2000 times 4000 times
|
80% energy 60% energy
|
Conclusion:
To ensure the smooth operation of your application,
EverExceed research and development engineers works day and night to research and design the state of art
Lithium Iron phosphate batteries with the perfect charging and discharging parameters which confirms the longest cycle life available for the battery. So choose EverExceed as your brand for the complete reliability.
