Method for measuring first coulombic efficiency of lithium batteries and material system preference method

Abstract

The invention discloses a method for measuring the first coulombic efficiency of lithium batteries and a material system preference method. The preference method comprises the following steps: a) preparing a plurality of lithium batteries of different material systems, and connecting the batteries after liquid injection and ageing to a coulombic metering device; b) vacuumizing the interiors of thebatteries by using a vacuumizing device; c) charging the batteries, recording charging coulombic values, then discharging the batteries, and recording discharging coulombic values; d) calculating thefirst coulombic efficiency of each lithium battery according to the recorded coulombic values; and e) comparing the first coulombic efficiency of each battery, and preferably selecting a material system of an lithium ion battery. The method vacuumizes the interiors of the batteries to eliminate bubbles generated in the pre-charging process when the batteries are charged and discharged for the first time so that the measured first coulombic efficiency is not affected by pre-charging gas production to better reflect the electrochemical properties of a battery system, and the preference of the battery material system is achieved.

Description

technical field [0001] The invention relates to the field of battery manufacturing, in particular to a method for measuring the first coulombic efficiency of a lithium battery and an optimal method for its material system. Background technique [0002] The first charge-discharge coulombic efficiency of lithium-ion batteries can directly reflect the electrochemical performance of the battery system. The battery system with different materials will be reflected in the Coulombic efficiency measured for the first time. Generally, the low efficiency of battery negative electrode materials will affect the performance of the corresponding positive electrode capacity. For example, the same lithium cobalt oxide positive electrode system corresponds to two batteries with two different negative electrodes. If the measured Coulombic efficiencies of the two systems are 92% and 91% respectively %, because it is significantly lower than the efficiency of lithium cobaltate, it shows that t...

AI Technical Summary

Problems solved by technology

When the gas exists as tiny bubbles in the liquid, under the action of surface tension, the bubbles will not float up due to density differences (equivalent to capillaries), but will stick to places with high interfacial tension such as pole pieces and shells. The current opening formation cannot completely remove the gas

The air bubbles between the pole pieces are equivalent to insulators, which will partially prevent the extraction and insertion of lithium ions, which will have a greater impact on the initial charge and discharge capacity of the battery cell.

Moreover, the opening method cannot prevent the moisture in the air, CO 2 When the gas enters the battery, it will cause side reactions, because water will interact with LiPF 6 The reaction produces LiF, which reduces the total amount of active lithium and reduces the reversible capacity of the battery. 2 O and HF can also react with the SEI film, causing the SEI layer formed during the formation of the battery to be destroyed and generate gas, which will have a negative impact on the battery, such as reducing the capacity of the battery cell and causing the shell of the battery cell, thus affecting the battery. The first coulombic efficiency value measurement of lithium-ion battery, resulting in the measured coulombic efficiency value cannot effectively evaluate the performance of the battery and guide the design of the battery material system

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