Positive Electrode Resistance Ratio for Low-Temperature Li-Ion Life
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Solution Overview
Problem
Lithium secondary batteries face challenges with carbon-based negative electrode materials having low capacity per unit mass and silicon-based compounds experiencing sudden deterioration at low temperatures, while existing methods like HPPC struggle to individually diagnose the state of positive and negative electrodes.
Innovation Solution
A positive electrode with a defined resistance component ratio (Rct / Rs ≥ 2) is used, analyzed through electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT), adjusting the positive electrode's reaction resistance to indirectly control the negative electrode's performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based compounds are used as negative electrode materials to increase capacity, then capacity per unit mass is improved, but sudden deterioration occurs and life is reduced at temperatures below room temperature
Solution Approach 1:
The patent changes the resistance parameters of the positive electrode by controlling the ratio of charge transfer resistance to surface resistance (Rct/Rs ≥ 2). This parameter adjustment indirectly controls the reaction resistance of the negative electrode, preventing sudden deterioration at low temperatures while maintaining high capacity from silicon-based materials
Solution Approach 2:
The positive electrode acts as an intermediary to indirectly control the negative electrode's reaction resistance. By adjusting the positive electrode's resistance characteristics, the patent mediates the problematic direct reaction at the silicon-based negative electrode, preventing deterioration without reducing capacity
2Quantity of substance
If HPPC method is used to measure battery performance, then overall performance evaluation is achieved, but individual diagnosis of positive and negative electrodes is not possible
Solution Approach 1:
The patent segments the battery diagnosis into individual electrode assessments by measuring and analyzing the resistance characteristics (Rct and Rs) of the positive electrode separately. This segmentation enables individual diagnosis of the positive electrode's state, which can then be used to infer the negative electrode's condition, overcoming the limitation of bulk-only measurement methods
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
Improves the life and performance of lithium secondary batteries by individually analyzing and diagnosing the positive and negative electrodes, preventing deterioration and enhancing capacity characteristics.
Implementation Method 1
analyzed through electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT), adjusting the positive electrode's reaction resistance
Implementation Method 2
R ct refers to a charge transfer resistance of the positive electrode measured in a first frequency domain
Data Source
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AI summary
The present invention relates to a positive electrode comprising a positive electrode active material, wherein a resistance component ratio, as defined by equation 1 below, is 2 or more. [Equation 1] Rct / Rs. In the equation, Rct means a charge transfer resistance of the positive electrode, which is measured in a first frequency range for a secondary battery comprising the positive electrode, Rs means a surface or interface resistance of the positive electrode, which is measured in a second frequency range for the secondary battery comprising the positive electrode, the first frequency range is from 1 Hz to 1 kHz, and the second frequency range is from more than 1 kHz to 1,000 kHz.