Charging lithium battery self-discharge resonance factor and measurement method

　　Author ：Iflowpower – Portable Power Station Supplier

This paper describes the effects of positive electrode materials, negative electrode materials, electrolytes, and storage environments on the self-discharge rate of lithium ion batteries. At the same time, it introduces the current commonly used traditional lithium-ion battery self-discharge rate measurement method and new self-discharge rate rapid measurement method. From Guoxuan high-tech engineer, welcome everyone to share! Lithium-ion battery self-discharge reactions are not preventable, but there is not only the reduction in battery itself, but also seriously affect the battery or cycle life.

The self-discharge ratio of the lithium-ion battery is generally 2% to 5% per month, and can fully meet the requirements of the monomer battery. However, once the monomer lithium ion battery is assembled into a module, due to the characteristics of each monomer lithium ion battery, the end voltage of each monomer lithium ion battery cannot be completely consistent after each charge and discharge, so that A monomer battery in a lithium-ion battery module appears, the performance of monomer lithium ion battery will deteriorate. As the number of charge and discharges have increased, the degree of deterioration will further exacerbate, and the cycle life has dropped sharply than the unpaired monomer battery.

Therefore, in-depth research on the self-discharge rate of the lithium ion battery is the urgent need of battery production. First, the self-discharge of the self-discharge factor battery self-discharge phenomenon refers to the phenomenon of self-loss when the battery is in turn, and it is also known as a chargeable capacity. Self-discharge can generally be divided into two types: reversible self-discharge and irreversible self-discharge.

The loss capacity can be reversible to compensate for reversible self-discharge, and the principle is similar to the normal discharge reaction of the battery. The loss capacity cannot obtain compensation self-discharge to irreversible self-discharge, and it is important reason that the inside of the battery has occurred inveracted, including the positive electrode and the electrolyte reaction, the electrolytic electrolytic solution, the reaction caused by the electrolyte autobiosis, and when manufactured The irreversible reaction caused by micro short circuits caused by impurities. The influencing factors of self-discharge are as described below.

1 The influence of positive electrode material is important is that the positive electrode material transition metal and impurities are short-discharged within the negative electrode precipitation, thereby newly discharged from a lithium-ion battery. Yah-Meiteng et al. Studied the physical and electrochemical properties of two LIFEPO4 positive materials.

The study found that the self-discharge rate of the iron impurity content in the raw materials and the charge and discharge process were high, the reason was that the iron was gradually reduced by the negative electrode, piercing the diaphragm, resulting in short circuit in the battery, thereby causing a higher self-discharge. 2 The effect of the negative electrode material on the self-discharge is important due to the irreversible reaction of the negative electrode material and the electrolyte. As early as 2003, Aurbach et al.

Proposed that the electrolyte was restored and released the gas, so that the surface of the graphite part was exposed to the electrolyte. During the charge and discharge process, lithium ion is inherently, the graphite layered structure is easily destroyed, resulting in larger self-discharge ratios. 3 Impact of the electrolytic solution electrolyte: the corrosion of the electrolyte or impurities on the surface of the negative electrode; the electrode material is dissolved in the electrolyte; the electrode is dissolved by the electrolytic solution is dissolved by the insoluble solid or gas to form a passivation layer, etc.

At present, a large number of research workers are committed to developing new additives to inhibit the effects of electrolyte on self-discharge. Junliu et al. MCN111 battery electrolyte additive to add additives, found that the battery high temperature cycle performance is improved, and the self-discharge rate is generally lowered.

The reason is that these additives can improve the SEI membrane to protect the battery negative electrode. 4 Storage status storage status General influencing factors are storage temperature and battery SOC. In general, the higher the temperature, the higher the SOC, the larger the battery's self-discharge.

TAKASHI et al. Capable experiments on phosphate ion batteries under resetting conditions. The results show that the capacity retention ratio gradually decreases with the shelf time, and the battery is raised.

Liu Yunjian and others use a commercial lithium manganate powered lithium battery. It has found that the relative potential of the positive electrode is getting higher and higher. The relative potential of the negative electrode is increasingly Low, its reducing property is also getting stronger, both can accelerate MN precipitation, resulting in an increase in self-discharge rate.

5 Other factors affect the factors of battery self-discharge rate, except for several described above, there are also the following aspects: In the production process, the burrs that occur when the pole is cut, and the production environment is introduced in the battery. Impurities, such as dust, metal powder on the plate, etc., these may cause the internal micro-short circuit of the battery; there is an external electronic circuit when the external environment is wet, the outer line insulation is not completely, the battery case is poor, resulting in an external electronic circuit, resulting in Self-discharge; during long-term storage, the active material of the electrode material and the bonding of the current collector, resulting in a decrease in capacity, and the self-discharge increases.

Each of the above factors or a combination of multiple factors can cause the self-discharge behavior of the lithium-ion battery, which is difficult to find and estimate the storage performance of the battery. Second, the measurement method of self-discharge ratio can be seen by the above analysis, since the lithium ion battery self-discharge rate is generally low. The self-discharge rate itself is affected by temperature, use of cycles and SOC, so accurate measurement of self-discharging of the battery is very difficult and time consuming.

1 Self-discharge rate Traditional Measurement Method Currently, the traditional self-discharge detection method has the following three types: Discharge to determine the capacity loss of the battery. The self-discharge rate is: in the form of: c is the rated capacity of the battery; C1 is discharge capacity. After the opening is put, the residual capacity of the battery can be obtained for the battery.

At this time, the battery cell is again charged and discharge cycle operation again, determine the full capacity of the electric garlic at this time. This method can determine that the battery is not reversible capacity loss and reversible capacity loss. ● Open-circuit voltage attenuation rate Measurement method The open circuit voltage and battery charge state SOC have a direct relationship, as long as it measures the change rate of the OCV of the battery in a period of time, that is, the method is simple, simply records the voltage of the battery during any time.

Further, according to the correspondence between the voltage and the battery SOC, the charge state of the battery can be obtained. The self-discharge rate of the battery can be obtained by the calculation of the attenuation of the voltage attenuation and the calculation of the attenuation capacity corresponding to the unit time. ● Capacity holding method Measures the battery's desired opening voltage or the power required to save, resulting from the self-discharge rate of the battery.

That is, the charging current when the battery open circuit is measured, and the battery self-discharge rate can be considered as the measured charging current. 2 Self-discharge Rate Rapid Measurement Method Due to the long time required for the conventional measurement method, the self-discharge rate is only a method of filtering the battery in the battery detection process due to the long time required for the conventional measurement method. The emergence of a large number of new and convenient measuring methods, saving a lot of time and energy for battery self-discharging measurements.

● Digital control technology digital control technology is a new self-discharge measurement method of derived self-discharge measurement method based on traditional self-discharge measurement methods. This method has the advantages of short, high precision, high precision, simple equipment. ● Equivalent circuitry equivalent circuit method is a new self-discharge measurement method, which simulates the battery into an equivalent circuit, which can quickly and effectively measure the self-discharge rate of lithium-ion batteries.

Third, measuring the meaning of self-discharge ratio As an important performance index of lithium ion battery, it has an important impact on the screening and gratuation of the battery, so the self-discolidation rate of lithium-ion batteries has far-reaching significance. 1 Predict the problem of the same bobbin in the same bob, the materials used, the materials used and the production control are basically the same. When individual battery is obviously large, the reason is probably due to impurities and burr piercing diaphragm.

Micro short circuit. Because the impact of micro-short to the battery is slow and irreversible. Therefore, the performance of such batteries does not differ much from normal batteries in a short period of time, but with the gradual deepening of internal irreversible reactions, the performance of the battery will be much lower than its factory performance and other normal battery performance.

Therefore, in order to ensure the quality of the factory battery, the self-discharged battery must be removed. 2 To group the battery to group lithium ion batteries to be better consistency, including capacity, voltage, internal resistance, and white discharge rate, etc. The impact of the battery's self-discharge rate on the battery pack is an important manifestation.

Once assembled into a module, due to the self-discipline of each monomer lithium ion battery, the voltage will decrease in different degrees, in series during the shelving or cycle Under charging, it is currently equal, so it may be overcharged or unfilled in the lithium-ion battery module after charging, and the performance will gradually deteriorate with the number of charge and discharges. Circulating life compared to unpaired monomer batteries. Therefore, the battery pack requires accurate measurement and screening of the self-discipline of lithium ion batteries.

3 Battery SOC estimation The correcting the load is also called the remaining power, which represents the ratio of the battery used for a period of time or long-term she holds the remaining capacity and its fully charged state, which is commonly used. Self-discharge rate about SOC estimation of lithium ion batteries has important reference value. After the self-discharge current, the correction of the start value of the SOC can improve the SOC estimation accuracy.

On the one hand, the customer can estimate the time or travel distance of the product according to the remaining power; on the other hand, the SOC prediction accuracy of BMS can effectively prevent the battery overcharge Overlant, extend battery life. .