Impact of water on lithium battery productio process

In the process of lithium battery, water is a factor that cannot be ignored. water has a very important impact on the performance and service life of lithium batteries. In this article, we will introduce the effects and hazards of water on the lithium battery process, and how to control water to ensure the quality and performance of lithium batteries.
Table of Contents

Impact of water on lithium battery process

1. Impact of water on the safety of lithium batteries

Water is one of the harmful substances in lithium batteries. Excessive water can lead to safety problems such as short-circuiting, expansion and rupture inside lithium batteries. The main way for water to enter into the interior of lithium battery is the water brought in from raw materials and production process. Therefore, in the production process of lithium battery, the water content must be strictly controlled to ensure the safety of lithium battery.

2. The effect of water on the performance of lithium battery

Water not only affects the safety of lithium battery, but also affects its performance. The right amount of water can promote the electrochemical reaction of lithium battery, improve the capacity and charging and discharging of lithium ion battery.

However, excessive water will lead to a decline in battery performance and shorten the service life of the battery. Therefore, in the production process of lithium batteries, the water content needs to be strictly controlled to obtain the best battery performance.


Hazards of water on lithium batteries

Battery swelling and leakage

If the water content in the lithium-ion battery is too much, it will react with the lithium salt in the electrolyte to form HF:

H2O + LiPF6 → POF3 + LiF + 2HF

Hydrofluoric acid (HF) is a very corrosive acid, which is very destructive to battery performance:

HF will corrode the metal parts inside the battery, the battery case, and the seal, which in turn will eventually cause the battery to break and leak.

HF will destroy the Solid-Electrolyte-Interface inside the battery and will react with the main components of the SEI membrane:

Li2CO3 + 2HF → H2CO3 + 2LiF

Finally, LiF precipitation is generated inside the battery, causing irreversible chemical reactions of lithium ions in the lithium ion battery anode, consuming active lithium ions, and the energy of the battery is reduced.

When there is enough moisture, more gas is produced, and the pressure inside the battery becomes greater, which causes deformation of the battery under stress, and there is a danger of battery bulging and leakage.

On the market during the use of cell phones or digital electronic products encountered in the battery bulging, open the cover of the situation, most of them are due to the high internal water of lithium batteries, gas production caused by bulging.


The internal resistance of the battery becomes bigger

Battery internal resistance is one of the most important performance parameters of the battery, it is the main symbol to measure the difficulty of ion and electron transmission inside the battery, which directly affects the cycle life and operation status of the battery; the smaller the internal resistance is, the smaller the voltage occupied when the battery is discharged, and the more energy it outputs.

When the water content increases, POF3 and LiF precipitation will be generated on the surface of Solid-Electrolyte-Interface of the battery, destroying the denseness and homogeneity of the SEI membrane, resulting in the gradual increase of the internal resistance of the battery, and the discharge capacity of the battery decreases continuously.

Shortened cycle life

Excessive water content destroys the SEI film of the battery, the internal resistance gradually rises, the discharge capacity of the battery becomes smaller and smaller, and the use time of the battery becomes shorter and shorter each time the battery is fully charged, the number of times the battery can be used normally (cycle) will naturally become less, and the use time (life) of the battery will be shortened.


Sources of water in the production of lithium batteries

In the manufacturing process of lithium battery, the source of moisture can be divided into the following aspects:

1. Moisture brought in by raw materials

  • Positive and negative materials: positive and negative active substances are micron and nanometer particles, which are very easy to absorb water in the air; especially the ternary or binary cathode materials with high Ni (nickel) content have a large specific surface area, and the surface of the material is very easy to absorb water and react. If the storage environment of the coated pole piece has high humidity, the surface coating of the pole piece will also absorb the moisture in the air quickly.
  • Electrolyte: the solvent component in the lithium ion battery electrolyte will react with water molecules; the solute lithium salt in the electrolyte is also prone to absorbing water and reacting chemically; therefore, there will be a certain amount of water inside the electrolytic; if the electrolyte is stored for a long time or at too high a temperature in the storage environment, the water content inside the electrolyte will also rise.
  • Separator: The separator is a porous plastic film (PP/PE material) which is also highly absorbent.

2.Water added in the pulping of electrode sheet

Water will be added to the negative electrode pulping and stirred with raw materials, and then coated, so the negative electrode sheet itself contains water. In the subsequent coating process, although there is heating and drying, there is still a considerable part of water adsorbed inside the coating of the pole piece.


3. Workshop environment moisture

  • Moisture contained in the air in the workshop: Moisture in the air, generally measured in relative humidity. Different seasons, different weather, the relative humidity varies greatly; spring, summer air humidity is relatively large (more than 60%), fall, winter air is drier humidity is smaller (less than 40%); rainy day air humidity is larger, sunny day air humidity is smaller. So different air humidity, the water content in the air is different.
  • Water produced by the human body (human sweat, exhaled breath, hand washing water)
  • Water brought in by various auxiliary materials and paper (carton, rags, statements)

How to control the water in llithium batteries

1. Control of raw materials

In the production process of lithium battery, the control of raw materials is very important. Among them, raw materials such as electrolyte, separator, positive and negative electrode materials may contain water. Therefore, during the procurement process, these raw materials need to be strictly quality inspected to ensure that their water content meets the standard.

Meanwhile, in the process of storage and use, corresponding measures need to be taken, such as dry storage and avoiding direct sunlight, etc., in order to prevent the impact of water on raw materials.

2. Production process control

In the lithium battery production process, a series of measures need to be taken to control water. For example, in the electrode preparation process, it is necessary to ensure that the electrode material mixing and coating process does not introduce excessive water.

Meanwhile, in the battery assembly process, it is necessary to select the appropriate diaphragm and electrolyte, and ensure that the assembly environment has low relative humidity. In addition, in the battery formation process, the formation temperature and time need to be controlled to avoid the influence of water on the battery performance.


3. Equipment selection and control

In the production process of lithium battery, the selection and control of equipment is also very important. In order to effectively control the water content, it is necessary to choose the appropriate drying equipment and technology, such as vacuum drying, hot air drying and so on.

At the same time, regular inspection and maintenance of the production equipment is also needed in the production process to ensure its normal operation and prevent water leakage and other problems.

4. Testing and analysis

In order to ensure that the quality and performance of lithium batteries meet the requirements, the battery needs to be tested and analyzed. Among them, water detection is a very important part. Commonly used water detection methods include gas chromatography, mass spectrometry, Karl Fischer method and so on.

The water content in the battery can be effectively detected by these detection methods and controlled and processed accordingly. At the same time, the performance test of the battery also needs to be carried out regularly to understand the use of the battery and the trend of performance changes.


In the process of lithium battery, water is a very important influence factor. In order to ensure that the quality and performance of lithium batteries meet the requirements, the water content must be strictly controlled.

Through the comprehensive control and treatment of raw materials, production process, equipment and testing can effectively ensure that the water content of lithium batteries meet the requirements and obtain the best battery performance and service life.

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