With the development of science and technology and the maturity of technology, the application of forklift lithium battery is more and more extensive. Forklift lithium battery has the advantages of high single voltage, relatively light weight and environmental friendliness, etc., but after several cycles of charge and discharge cycle, the performance of battery capacity and so on will decline. Under the same condition, the faster the battery capacity decays, the worse the battery quality will be. The cycle performance of forklift lithium battery is an important index to measure its quality.

The cycle of charge and discharge of forklift lithium battery is a complex process of physical and chemical reaction. On the one hand, it is related to the characteristics of the battery itself, such as design, manufacturing process and degradation of material performance. On the other hand, the battery is affected by the outside world, such as the operating environment and charging and discharging system. The factors affecting the cycle life of forklift lithium battery are analyzed below.

Brief introduction to structure and principle of lithium battery for forklift truck

Forklift lithium battery is mainly composed of anode and cathode materials, electrolyte, diaphragm, collector fluid and battery shell. Anode and cathode materials are composed of two different lithium ion imbedding compounds. During charging, the lithium ions are released from the positive electrode and embedded into the negative electrode through the electrolyte and the membrane. In the first charge and discharge process of forklift lithium battery, a passivation film can be formed on the phase interface between anode and electrolyte. It ACTS as a diaphragm between the electrode and the electrolyte. It is an electronic insulator but a good conductor of lithium ions. Lithium ions can be freely embedded and disintegrated through the passivation layer, and it has the characteristics of solid electrolyte.

Influence of design and manufacturing process

Material selection is the most important factor in battery design. Different materials have different properties and the developed batteries have different performance. The cycle life of the battery will be long if the materials of positive and negative electrodes are well matched. In the aspect of ingredients, we should pay attention to the addition of positive and negative materials. Generally speaking, in the design and assembly process, the negative electrode capacity is generally required to be more than the positive electrode. If not, lithium will be precipitated from the negative electrode in the charging process, and lithium dendrites will be formed, thus affecting the safety. Too much of the negative pole relative to the positive pole, the positive pole may be excessive de-lithium, causing structural collapse.

Electrolyte is also an important factor in the reversible capacity of the battery. The process of the electrode material removing and intercalating lithium ions is always the process of interaction with the electrolyte, which has an important influence on the interface state and internal structure of the electrode material [3]. Electrolyte loss during interaction with anode and cathode materials and consumption of electrolyte when battery is converted into SEI film and precharge also affect battery life.

Forklift lithium battery manufacturing process mainly includes: positive and negative electrode batching, coating, production, winding, into the shell, liquid injection, sealing, into and so on. In the process of battery production, every step of the process is very strict. Any process not well controlled may affect the battery cycle performance.

In the process of positive and negative electrode batching, attention should be paid to the amount of binder, mixing speed, slurry concentration, temperature and humidity, and ensure that the material can be dispersed evenly.

In the process of coating, under the premise of ensuring the high specific energy of the battery, reasonable control of positive (negative) electrode coating amount and appropriate reduction of electrode thickness are conducive to reducing the battery attenuation rate. The coated electrode sheet should be further compaction by roller press. Appropriate positive electrode compaction density can increase the discharge capacity of the battery, reduce the internal resistance, reduce the polarization loss, and extend the cycle life of the battery.

When winding, the coiled cell should be tight, not loose. The more tightly the diaphragm and the positive and negative poles are rolled, the smaller the internal resistance will be. However, the more tightly the membrane is rolled, the more difficult it will be to wet the plate and the diaphragm, resulting in a smaller discharge capacity. Too loose coiling will cause excessive expansion of the plate in the filling and releasing process, increase the internal resistance, reduce the capacity and shorten the cycle life.