About Self-discharge of Lithium ion Solar Batteries

What Is The Self-discharge of Lithium ion Solar Batteries?

Self-discharge of lithium ion solar batteries is a normal chemical phenomenon, which refers to the loss of charge of a lithium battery over time when it is not connected to any load. The speed of self-discharge determines the percentage of the original stored power (capacity) that is still available after storage. A certain amount of self-discharge is a normal property caused by the chemical reactions that occur within the battery. Lithium-ion batteries typically lose about 0.5% to 1% of their charge per month.

When we put a battery containing a certain amount of charge at a certain temperature and keep it for a certain period of time, To make a long story short, self-discharge is a phenomenon in which Solar lithium battery itself is lost due to subsidiary Knowledge of self-discharge is important for selecting the right lithium-ion battery system for certain applications.

The Importance Li ion Solar Battery of Self-discharge.

Currently, li ion battery are used more and more widely in laptop,digital camera and other digital devices, besides, it also  have board prospects in vehicle, communication base station, battery energy storage power station and some other areas.Under these circumstances,battery is not only show up alone like in just a cell phone but also will show up in series or in parallel.

In the home off-grid solar system, the capacity and life span of the li ion solar battery pack is not just only related to every single battery, but also more related to the consistency between every single li ion battery.Poor consistency can greatly drag the manifestation of the battery pack.

The consistency of the li ion solar battery self-discharge is one of the important part of the effect factor,the SOC of li ion solar battery with inconsistency self-discharge will have a biggish difference after a period of storage and its capacity and security will be greatly affected. It help us to improve the overall level of our li ion battery pack,get longer life and lower the fraction defective of the products through our studying.

What Causes Solar Lithium Batteries Self-discharge?

Solar lithium batteries are not connected to any load when open circuit, but the power is still decreasing, the following are the possible causes of self-discharge.

1. Internal electron leakage caused by partial electron conduction or other electrolyte internal short circuit

2. External electron leakage caused by poor insulation of Solar lithium battery battery seal or gasket or insufficient resistance between external cases (external conductor, humidity).

a.Electrode/electrolyte reaction, such as anode corrosion or cathode recovery due to electrolyte and impurities.

b.Local decomposition of electrode active material

3.Passivation of electrode due to decomposition products (undissolved substances and adsorbed gases)

4. Mechanical wear of electrode or resistance (between electrode and collector) increases with the increase of current in the collector.

5. Periodic charging and discharging can lead to unwanted lithium metal deposits on the lithium ion anode (negative electrode)

6. Chemically unstable electrodes and impurities in the electrolyte cause self-discharge in solar lithium batteries.

7. The battery is mixed with dust impurities during the manufacturing process, impurities can lead to a slight conduction of the positive and negative electrodes, causing the charge to be neutralized and damage the power supply.

8. The quality of the diaphragm will have a significant impact on the self-discharge of solar lithium battery

9.The higher the ambient temperature of the solar lithium battery, the higher the activity of the electrochemical material becomes, resulting in more capacity loss during the same period.

The Influence of Lithium ion Battery for Solar Self-discharge.

1. Self-discharge of lithium ion solar batteries will cause a decrease in storage capacity.

2. The self-discharge of metal impurities causes the diaphragm aperture to block or even pierce the diaphragm, causing a local short circuit and endangering the safety of the battery.

3. The self-discharge of lithium ion solar batteries causes the SOC difference between the batteries to increase, which reduces the capacity of the solar lithium battery bank.

Due to the inconsistency of self-discharge, the SOC of the lithium battery in the solar lithium battery bank is different after storage, and the function of the solar lithium battery is also reduced. After customers get the solar lithium battery bank that has been stored for a period of time, they can often find the problem of performance degradation. When the SOC difference reaches about 20%, the capacity of the combined lithium battery is only 60% to 70%.

4. If the SOC difference is too large, it is easy to cause overcharge and overdischarge of the lithium ion solar battery.

The difference between chemical self-discharge and physical self-discharge of lithium ion solar batteries

1. lithium ion solar batteries high temperature self-discharge versus room temperature self-discharge.

Physical micro-short circuit is significantly related to time, and long time storage is a more effective option for physical self-discharge.

The way of high temperature 5D and room temperature 14D is: if the self-discharge of lithium ion solar batteries is mainly physical self-discharge, room temperature self-discharge/high temperature self-discharge is about 2.8; if it is mainly chemical self-discharge, room temperature self-discharge/high temperature self-discharge is less than 2.8.

2. Comparison of self-discharge of lithium ion solar batteries before and after cycling

Cycling will cause micro-short circuit melting inside the lithium solar battery, thus reducing the physical self-discharge. Therefore, if the self-discharge of li ion solar battery is mainly physical self-discharge, it will be significantly reduced after cycling; if it is mainly chemical self-discharge, there is no significant change after cycling.

3. Leakage current test under liquid nitrogen.

Measure the leakage current of li ion solar battery under liquid nitrogen with a high voltage tester, if the following conditions occur, it means that the micro short circuit is serious and the physical self-discharge is large.

 >> Leakage current is high at a particular voltage.

>> The ratio of leakage current to voltage varies greatly at different voltages.

4. Comparison of li ion solar battery self-discharge in different SOC

The contribution of physical self-discharge is different in different SOC cases. Through experimental verification, it is relatively easy to distinguish the li ion solar battery with abnormal physical self-discharge at 100% SOC .

Lithium Battery Solar Self-discharge Test

Similar to some chain reactions, the rate and intensity of their occurrence is influenced by the environment. Lower temperature levels are usually much better because the cold slows down the chain reaction and therefore reduces any type of undesirable lithium ion solar battery self-discharge. So, one of the most logical things to do seems to be to keep the battery in the refrigerator, right? No! On the other hand: you must always prevent putting batteries in the refrigerator. Humid air in the refrigerator can likewise cause discharge. Especially when you take the lithium batteries out, condensation can damage them - making them no longer fit for use.

It is best to store your lithium solar batteries in a cool but completely dry place, preferably between 10 and 25°C. For additional advice related to lithium battery storage, please read our previous blog site. Some basic actions can be required to reduce unwanted lithium-ion solar battery self-discharge. If you are not completely sure of the power level of your batteries, you can always recharge them. This way, you can make sure your lithium solar batteries are up to the task - and you can get the most out of your lithium solar battery pack day in and day out.