Thin-Separator Secondary Battery for High-Voltage Self-Discharge Control
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Solution Overview
Problem
Secondary batteries with high output voltage and thin separators face issues of self-discharge due to weakened separator isolation, leading to series voltage differences and reduced cycling performance in battery modules.
Innovation Solution
Incorporating a thin separator with a thickness of 3-7 μm and using electrolyte and positive electrode nitrile-containing additives within specific mass percentage ranges (0.3≤z≤3.3, 0<x≤2.3, 0<y≤1) to synergistically interact with the separator, reducing transition metal ion dissolution and diffusion impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a thin separator is used to enhance energy density, then the energy density is improved, but the separator's isolation effect is weakened leading to self-discharge
Solution Approach 1:
The separator is constructed as a composite structure with a base film layer and a coating layer containing Al2O3 particles and PVDF binder. This composite structure provides both the thin profile needed for high energy density (3-7 μm base film) and the enhanced isolation properties to prevent self-discharge, resolving the contradiction between thinness and effectiveness.
Solution Approach 2:
The separator exhibits different properties in different regions: the base film provides mechanical strength and basic separation, while the coating layer with Al2O3 particles and PVDF provides enhanced thermal stability and isolation. This local differentiation allows the separator to be thin overall while maintaining high isolation performance at critical interfaces.
2Quantity of substance
If high output voltage is used to enhance capacity and energy density, then the capacity and energy density are improved, but transition metal ion dissolution increases causing self-discharge
Solution Approach 1:
The PVDF binder and Al2O3 particles in the separator's coating layer act as intermediary substances that interact with transition metal ions. The PVDF polymer matrix and alumina particles adsorb and stabilize dissolved ions, preventing them from migrating between electrodes and causing self-discharge, thus enabling high voltage operation without the harmful effects of ion dissolution.
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
Alleviates self-discharge during charging and discharging, maintaining consistency in output voltages and capacities, and improving cycling performance under high voltages and temperatures.
Implementation Method 1
the electrolyte nitrile-containing additive and the positive electrode nitrile-containing additive synergistically interact with the separator, reducing the dissolution of transition metal ions (for example, Co ions) inside the secondary battery under high voltages and controlling diffusion impedance
Data Source
AI summary
A secondary battery includes an electrode assembly and an electrolyte, where the electrode assembly includes a positive electrode plate, and a separator; the positive electrode plate includes a positive electrode active material layer; the positive electrode active material layer includes a positive electrode active material; the positive electrode active material includes a transition metal element; the transition metal element includes at least one of Co, Ni, Mn, Fe, or V; and the separator includes a base film, where a thickness of the base film is D μm, and 3≤D≤7. The secondary battery includes an electrolyte nitrile-containing additive and a positive electrode nitrile-containing additive, where based on a mass of the electrolyte, a mass percentage of the electrolyte nitrile-containing additive is x %, and based on a mass of the positive electrode active material layer, a mass percentage of the positive electrode nitrile-containing additive is y %; where x+y=z, 0.3≤z≤3.3, 0≤x≤2.3, and 0<y≤1.