Li-Ion Cell Pre-Doping Chemistry for Alloy Anode Cycle Durability
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in enhancing charge/discharge efficiency, maintaining high capacity and output, preventing positive electrode material deterioration during pre-doping, and reducing micro-short circuit rates, especially when using alloy-based active materials.
Innovation Solution
A lithium ion secondary battery design incorporating a positive electrode with a transition metal oxide capable of occluding and releasing lithium ions, containing Ni atoms, and a specific range of Ni3p peak energy difference, along with a negative electrode comprising carbon and alloy-based materials, optimized with a lithium compound and electrolyte composition to improve durability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pre-doping is performed by forming a lithium metal layer on the negative electrode surface, then charge/discharge efficiency is improved, but the negative electrode deteriorates due to volume expansion and heat effects
Solution Approach 1:
The patent introduces a lithium compound (such as lithium carbonate or lithium hydroxide) as an intermediary substance to perform pre-doping. This compound decomposes at moderate temperatures to release lithium ions, avoiding the direct contact and harmful effects of lithium metal while still achieving the desired pre-doping effect on the alloy-based active material.
Solution Approach 2:
The patent changes the physical and chemical parameters of the pre-doping process by using a lithium compound instead of lithium metal. The decomposition temperature of the lithium compound is controlled to be between 100°C and 300°C, which is lower than the melting point of lithium metal (180°C), allowing pre-doping to proceed under milder conditions that prevent negative electrode deterioration.
2Reliability
If pre-doping is performed using lithium carbonate to improve durability at high temperatures, then pre-doping can be carried out under mild conditions, but the positive electrode active material deteriorates due to reaction with lithium carbonate and CO2 gas causes separation and micro-short circuits
Solution Approach 1:
The patent extracts the harmful CO2 gas generation step from the pre-doping process by selecting lithium compounds that decompose without producing gas. This eliminates the cause of positive electrode material separation and micro-short circuits while retaining the beneficial pre-doping effect.
Solution Approach 2:
The patent converts the potential harm of using lithium compounds (which can react with positive electrode materials) into a benefit by carefully selecting compounds with decomposition temperatures below the reaction temperature with positive electrode materials. The decomposition occurs first, releasing lithium ions for pre-doping, before any harmful reactions with the positive electrode can occur.
3Quantity of substance
If alloy-based active material is used to enhance energy density, then energy density increases, but durability decreases due to large volume expansion and contraction
Solution Approach 1:
The patent applies pre-doping as a preliminary action before the alloy-based active material undergoes repeated volume expansion and contraction during charge-discharge cycles. By introducing lithium ions in advance, the material's structure is stabilized, reducing the mechanical stress and preventing deterioration that would otherwise occur during cycling.
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
The battery achieves enhanced charge/discharge efficiency, high capacity, and reduced micro-short circuit rates, while inhibiting positive electrode material deterioration and improving cycle characteristics.
Implementation Method 1
a transition metal oxide that is capable of occluding and releasing lithium ions
Implementation Method 2
an alloy-based active material, which contains atoms such as silicon or tin that form an alloy with lithium
Implementation Method 3
a nonaqueous electrolyte containing lithium ions
Data Source
AI summary
A lithium ion secondary cell comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte that contains lithium ions, the lithium ion secondary cell being such that: the positive electrode has a positive electrode current collector and a positive electrode active material layer; the positive electrode active material layer contains a positive electrode active material and a lithium compound; the positive electrode active material includes a transition metal oxide; the concentration of the lithium compound, which is the portion other than the positive electrode active material in the positive electrode active material layer, is 0.1-10 mass %; the negative electrode has a negative electrode current collector and a negative electrode active material layer; the negative electrode active material layer contains 50-95 mass % of a carbon material and 5-50 mass % of an alloy-based active material.