LR6 alkaline battery.The bumpy lithium battery technology is still on the way to maturity

　　The bumpy lithium battery technology is still on the way to maturity

　　The invention of lithium batteries has a history of 49 years, but the safety, energy density and price are still not close to the people. Looking at various information, all of them say that the process of lithium batteries is complicated, there are many preparation processes, thermal runaway is prominent, and failure analysis and verification are difficult to verify.

　　The invention of lithium batteries has a history of 49 years, but the safety, energy density and price are still not close to the people. Looking at various information, all of them say that the process of lithium batteries is complicated, there are many preparation processes, thermal runaway is prominent, and failure analysis and verification are difficult to verify.

　　First, let’s popularize the knowledge about lithium batteries. If you don’t like, skip it.

　　The capacity of lithium batteries is determined by the lithium ion content in the positive active material. Excessive positive electrode and uneven lithium ion gradient distribution in the electrolyte will precipitate lithium and produce dendrites, which can easily cause safety threats. The electrolyte plays a role in transporting lithium ions, and the amount must be guaranteed. The moisture in the battery will consume lithium ions and affect the capacity. At the same time, it is easy to react with the electrolyte and cause bloating. The diaphragm plays a filtering role and cannot be damaged, otherwise the positive and negative electrodes will come into contact and short circuit will occur.

　　If operated at high temperatures, the battery capacity will decrease faster and the lifespan will be shortened.

　　Low temperature lithium iron phosphate battery 3.2V 20A -20℃ charging, -40℃ 3C discharge capacity ≥70%

　　In particular, the abuse of lithium batteries is obvious, mainly thermal abuse, electrical abuse and mechanical abuse. Excessive heat and fire exposure are examples of thermal abuse. Overcharge, overdischarge, and external/internal short circuits are electrical abuses. Mechanical abuse includes impact, penetration, and bending.

　　All in all, for lithium battery production, the most important thing is to learn failure analysis. The methodology is to find the cause of quality problems, find the correct conclusion in a short period of time, and choose practical measures.

　　Failure analysis is very simple and mainly includes: clarifying the analysis object, determining the failure mode, studying the failure mechanism, determining the cause of the failure, and proposing preventive measures (including design improvements).

　　Whether a failure event is a major accident or a minor failure, the reasons always include six aspects: operators, mechanical equipment systems, materials, manufacturing processes, environment and management. The solutions are as follows.

　　First, comparison methods. Select a system that has not failed and can be compared with the failed system to identify differences. This will help identify the cause of the failure as quickly as possible.

　　Low temperature and high energy density 18650 3350mAh-40℃ 0.5C discharge capacity ≥60%

　　Charging temperature: 0~45℃ Discharge temperature: -40~+55℃ Specific energy: 240Wh/kg -40℃ Discharge capacity retention rate: 0.5C Discharge capacity ≥ 60%

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　　Second, historical method. The objective basis of the historical method is the movement changes and causal constraints of the material world. It is to infer the possible reasons for the current failure based on the past performance and change patterns of the equipment under the same service conditions.

　　Third, logical method. It is to analyze, compare, synthesize, and summarize based on background information (design, materials, manufacturing conditions, etc.) and failure site investigation materials as well as information obtained from analysis and testing, to make judgments and inferences, and then to derive possible causes of failure.

　　Regarding lithium battery failure, it is mainly divided into two categories: performance failure and safety failure.

　　Performance failure is when the performance of lithium batteries fails to meet the usage requirements and related indicators. It mainly includes capacity attenuation or diving, short cycle life, poor rate performance, poor consistency, easy self-discharge, high and low temperature performance attenuation, etc.

　　Safety failure refers to the failure of lithium batteries with certain safety risks due to improper use or abuse, mainly including thermal runaway, flatulence, leakage, lithium precipitation, short circuit, expansion and deformation, etc.

　　Fundamentally, however, failure boils down to the destruction of material properties and structure.

　　The author has a master's degree in materials and knows that behind all great creations are material innovations.

　　Material failure mainly refers to abnormalities in material structure, properties, morphology, etc. and mismatch between materials.

　　For example, the particles of the cathode material are broken due to uneven stress on the material caused by inconsistent local Li+ deintercalation rates. The silicon anode material is broken and pulverized due to volume expansion and contraction during charging and discharging. The electrolyte is decomposed or deteriorated due to the influence of humidity and temperature. The solvent co-embedded between the graphite anode and the additive propylene carbonate (PC) in the electrolyte. The problem is lithium precipitation caused by too small N/P (the ratio of the capacity of the negative electrode sheet to the capacity of the positive electrode sheet).

　　For today's moderately popular electric vehicles and hybrid vehicles, the core technology is the battery. Compared with 3C consumer batteries, although power batteries are expensive and have poor safety performance, they have high specific energy, long cycle life, and wider application scenarios.

　　Wide sea diving, sky high the birds to fly. As the times progress, power battery technology is changing with each passing day, and future improvements should focus on capacity and structure.

　　One thing is certain, no matter which technical route the battery manufacturer adopts, it must meet the conditions of high safety, wide range of environmental temperature differences, strong charging and discharging functionality, good rate discharge usability, and low cost.

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