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In the dynamic environment of charging and discharging during actual operations, lithium-ion batteries, despite being managed by the battery energy management system to function optimally, are susceptible to mechanical, electrical, and thermal stress under specific conditions like overcharging, over-discharging, and overheating. These occurrences can swiftly deteriorate battery performance, leading to internal short circuits and ultimately resulting in thermal runaway, posing a safety risk.

Investigation of Internal Short Circuit Mechanisms

Internal short circuits persist throughout a battery's life cycle and can be categorized into initial, intermediate, and final stages.

In the early stage, the voltage drop caused by the internal short circuit is gradual, generating minimal heat that the cooling system can disperse, causing insignificant temperature changes. This stage lasts longer and is harder to detect.

The intermediate stage witnesses a notable voltage drop and increased heat generation that accumulates due to insufficient dissipation, significantly raising battery temperature. It's shorter but more detectable.

The final stage sees the battery voltage dropping to 0V due to extensive short circuits, generating substantial instant heat, triggering thermal runaway. This stage is extremely brief and unstoppable.

Measures to Suppress Internal Short Circuits

Factors causing internal short circuits in batteries can broadly be divided into battery materials and processes, as well as battery design and usage. Approaches to inhibit and prevent internal short circuits from these perspectives are outlined below:

Battery Materials and Processes:

Enhancements in diaphragm and electrolyte materials, positive and negative electrode coatings, and improved production processes aim to reduce defects.

Use of ceramic diaphragms with high temperature resistance and low self-discharge rates, along with flame-retardant or ionic liquid electrolytes, effectively suppresses dendrite growth, reducing internal short circuit risks.

Application of low-conductivity coatings or positive temperature coefficient materials on the battery's collector or electrodes decreases internal short-circuit currents and heat generation during a short circuit, reducing the chances of triggering thermal runaway.

Optimization of battery cell production processes and material purification effectively filters out metal impurities, reducing the risk of metal particles piercing the diaphragm, which could lead to internal short circuits.

Employing advanced testing technology ensures battery structure integrity, processing precision, and pole alignment, minimizing potential internal short circuits.

Battery Design and Usage:

Battery Management System (BMS) sets up prudent battery warning and safety control strategies for real-time monitoring, timely detection, and elimination of units with internal short circuits.

Designing redundant cell charging, discharging, and equalization strategies reduces the risk of internal short circuits caused by high battery loads.

Hierarchical management of battery fuses—single fuse, module fuse, battery pack fuse, and vehicle load fuse—enables timely cutoff of internal short circuits, preventing their continuous development.

Reasonable internal battery cooling system design enhances thermal conductivity, preventing thermal runaway due to overheating.

Strategic battery internal heating system design preheats batteries to appropriate working temperatures during low-temperature charging, preventing dendrites from piercing the diaphragm and causing thermal runaway.