Positive Electrode Protective Film for Li-Ion Thermal Stability
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Solution Overview
Problem
Lithium-ion batteries face challenges in achieving higher energy density, safety performance, cycling performance, and longer service life, particularly in maintaining thermal stability and preventing side reactions at high temperatures.
Innovation Solution
The electrochemical apparatus incorporates a positive electrode plate with a specific DSC curve profile, featuring exothermic peaks that indicate a stable interfacial protective film, and controlled parameters such as electrolyte injection coefficient, formation voltage, and standing time, along with a positive electrode active material containing lithium transition metal composite oxides with doping elements like Al and Nb, to enhance thermal stability and prevent side reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the positive electrode active material is used without adequate protective film, then the energy density can be increased, but the thermal stability deteriorates and side reactions occur at high temperature
Solution Approach 1:
The patent applies preliminary action by forming an adequate protective film on the positive electrode active material surface through controlled formation processes (electrolyte injection coefficient, formation voltage, temperature, and standing time) before the battery enters service. This pre-formed protective film prevents thermal degradation and side reactions during subsequent high-temperature operation, resolving the contradiction between energy density and thermal stability.
2Reliability
If the protective film on positive electrode active material is enhanced, then the safety performance and cycling performance are improved, but the rate performance may be compromised due to increased interfacial resistance
Solution Approach 1:
The patent applies parameter changes by precisely controlling formation parameters (electrolyte injection coefficient from 3.0-6.0 mL/Ah, formation voltage 3.0-4.4 V, formation temperature 20-40°C, standing time 0.5-24 hours) to achieve optimal protective film properties. This balances film adequacy for safety with controlled interfacial resistance for acceptable rate performance.
3Duration of action of stationary object
If the formation temperature and standing time are increased to improve protective film quality, then the cycling performance is improved, but the manufacturing time and energy consumption increase
Solution Approach 1:
The patent applies parameter changes by optimizing formation temperature (20-40°C) and standing time (0.5-24 hours) within specific ranges to achieve adequate protective film formation. This balanced approach ensures sufficient cycling performance while controlling manufacturing time and energy consumption, avoiding excessive formation conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration improves the cycling performance, rate performance, and safety performance of the electrochemical apparatus by maintaining thermal stability and preventing side reactions, leading to better protection of the positive electrode active material and extended battery life.
Implementation Method 1
a DSC (differential scanning calorimetry) curve of the positive electrode plate has a first exothermic peak A1 and a second exothermic peak A2
Implementation Method 2
a DSC (differential scanning calorimetry) curve of the positive electrode plate has a first exothermic peak A1 and a second exothermic peak A2
Data Source
AI summary
An electrochemical apparatus, including a positive electrode plate, the positive electrode plate includes a positive electrode active material. When a state of charge of the electrochemical apparatus ranges from 90% to 100%, a DSC curve of the positive electrode plate has a first exothermic peak A1 and a second exothermic peak A2 in a temperature range of 150° C. to 400° C.; where based on a mass of the positive electrode active material, the first exothermic peak A1 is an exothermic peak closest to 400° C. with a peak intensity greater than 0.1 mW/mg, the second exothermic peak A2 is an exothermic peak closest to 150° C. with a peak intensity greater than 0.1 mW/mg, a difference between a peak position Ta of the first exothermic peak A1 and a peak position Tb of the second exothermic peak A2 ranges from 20° C. to 150° C. The electrochemical apparatus has good cycling, rate, and safety performances.