1、 Inconsistency analysis

(1) Definition of inconsistencyThe inconsistency of lithium-ion battery packs refers to the differences in parameters such as voltage, capacity, internal resistance, lifespan, temperature influence, and self discharge rate among individual batteries of the same specification and model after forming a battery pack. After manufacturing, there are certain differences in the initial performance of individual batteries. With the use of batteries, these performance differences continue to accumulate, and due to the different usage environments of individual batteries within the battery pack, the inconsistency of individual batteries gradually amplifies, accelerating battery performance degradation and ultimately leading to premature failure of the battery pack.

(2) The manifestation of inconsistencyThe inconsistency of lithium-ion batteries is mainly manifested in two aspects: differences in battery performance parameters (battery capacity, internal resistance, and self discharge rate) and differences in battery state of charge (SOC).

(3) The causes of inconsistencyThere are many reasons for inconsistency issues in lithium-ion batteries, mainly arising during the manufacturing and usage processes. Each stage of the manufacturing process, such as the uniformity of the slurry during batching, the control of surface density and surface tension during coating, can cause differences in the performance of individual batteries.

2、 Methods to improve battery consistency

(1) Control of production processThe control of the production process is mainly carried out from two aspects: raw materials and production technology. In terms of raw materials, try to select the same batch of raw materials to ensure consistency in particle size and performance. Strict regulation of the entire production process is necessary in terms of production technology, such as ensuring uniform mixing of the slurry and not placing it for a long time, controlling the speed of the coating machine to ensure the thickness and uniformity of the coating, inspecting the appearance of the polarizer, weighing and grading, controlling the amount of liquid injected and the conditions of formation, volume, and storage.

(2) Control of grouping processThe control of the battery pairing process mainly refers to the sorting of batteries. The battery pack adopts a unified specification and model of batteries, and the voltage, capacity, internal resistance, etc. of the batteries need to be measured to ensure the consistency of the initial performance of the batteries.

(3) Control of usage and maintenance processReal time monitoring of batteries. Consistency screening of batteries during grouping can ensure consistency during the initial use of the battery pack. If you want to understand the consistency of the battery during use, it is necessary to monitor the battery in real-time. Timely adjustment or replacement of extreme parameter batteries through real-time monitoring can ensure the healthy operation of the battery pack.

(4) Introduce a balanced management system. Using appropriate balancing strategies and balancing circuits for intelligent management of batteries. The current common balancing strategies include external voltage based balancing strategy, SOC based balancing strategy, and capacity based balancing strategy. The balancing circuit can be divided into passive balancing and active balancing according to the energy consumption mode. Active balancing, which can achieve non-destructive energy flow between batteries, is a hot research topic both domestically and internationally. The commonly used methods in active balancing include battery bypass method, switched capacitor method, switched inductor method, DC/DC conversion method, etc.

(5) Perform thermal management on the battery. In addition to keeping the working temperature of the battery pack within the optimal range as much as possible, thermal management of batteries should also strive to ensure consistent temperature conditions between batteries, thereby effectively ensuring performance consistency among batteries. Adopt reasonable control strategies. When the output power allows, try to reduce the depth of battery discharge as much as possible, while avoiding overcharging of the battery, which can extend the cycle life of the battery pack. Strengthen the maintenance of battery packs. Perform low current maintenance charging on the battery pack at regular intervals, and also pay attention to cleanliness.

3、 Lithium ion battery assembly method

(1) Voltage matching methodThe voltage matching method can be divided into static voltage matching method and dynamic voltage matching method. The static voltage grouping method, also known as the no-load grouping method, does not carry a load and only considers the battery itself. It measures the self discharge rate of the selected individual battery stored in a fully charged state after being left idle for several tens of days, as well as the open circuit voltage of the battery during different storage periods in a fully charged state. This method is the simplest to operate, but not accurate. The dynamic voltage matching method examines the voltage situation under load, but does not take into account factors such as load changes, so it is also inaccurate.

(2) Static capacity grouping methodCharge and discharge the battery under set conditions, calculate the capacity based on the discharge current and discharge time, and group the batteries according to their capacity size. This method is simple and easy to implement, but it can only reflect that the battery has the same capacity under specific conditions, and cannot explain the complete working characteristics of the battery, which has certain limitations.

(3) Internal impedance matching methodMainly considering the internal resistance of individual batteries, this method can achieve rapid measurement, but accurate measurement of internal resistance is difficult because the internal resistance of the battery changes with the discharge process.(4) Multi parameter matching methodBy considering multiple external conditions such as capacity, internal resistance, voltage, and self discharge rate, a battery pack with good consistency can be selected for comprehensive evaluation. But the premise of this method is that it needs to be accurate during single parameter sorting, and it also takes too long.

(5) Dynamic characteristic matching methodThe dynamic characteristic grouping method is to use the charging and discharging characteristic curves of batteries to sort and group them. The charge discharge curve can reflect most of the characteristics of the battery, and the dynamic characteristic grouping method can ensure the consistency of various performance indicators of the battery. The dynamic characteristic matching method has a large amount of data and is usually implemented through computer programs. In addition, this method reduces the utilization rate of battery assembly, which is not conducive to the reduction of battery assembly costs. The determination of standard curve or benchmark curve is also a difficulty in its implementation process.Haibo Industrial Lithium Iron Phosphate Battery Pack

  Haibo ElectricHB-LiFePO4 industrial lithium iron phosphate battery packIt is a professional and serialized product launched for the special needs and application characteristics of industrial enterprises. Mainly used in industrial power backup batteries, industrial special batteries, industrial energy storage and other fields, it can meet the application scenarios of high voltage levels and large capacity.

  HB-LiFePO4 industrial lithium iron phosphate battery packCarrying our companyIntelligent Battery Management System (BMS)By fully utilizing the advantages of high energy density, good temperature characteristics, superior charging and discharging performance, and green environmental protection, lithium batteries have the characteristics of safety, reliability, true maintenance free, and ultra long service life.

 New product promotion:

  HB-HTSM series high-temperature magnetic lithium iron phosphate battery packThe environment temperature in the steel/iron plant workshop is high, metal dust is severe, and vibration is generated during the operation of the train. Lead acid batteries have poor high-temperature performance, short lifespan, and are prone to bulging and leakage, causing short circuits and fires, posing safety hazards. Haibo Electric has launched the HB-HTSM series high-temperature magnetic lithium iron phosphate battery pack for this application scenario.

 

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