Li-Ion Positive Electrode Composition for SEI Lithium Loss
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Solution Overview
Problem
The cycle life of lithium-ion batteries is shortened due to irreversible capacity loss from the formation of a solid electrolyte interphase (SEI) on the negative electrode, especially with high-specific-capacity materials, leading to excessive consumption of active lithium sources.
Innovation Solution
An electrochemical apparatus with a positive electrode comprising a combination of first and second positive electrode materials, optimized sheet resistance, compacted density, and surface density, along with an electrolyte containing fluoroethylene carbonate to form a LiF-rich SEI film, which supplements lithium and enhances battery performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high-specific-capacity negative electrode materials (such as silicon alloy, tin alloy, oxides, or amorphous carbon) are used to increase energy density, then the specific capacity is improved, but the active lithium source is excessively consumed due to SEI formation and damage, leading to shorter cycle life
Solution Approach 1:
The patent introduces a preliminary lithium source in the form of a lithium foil layer positioned between the positive and negative electrodes. This preliminary lithium source is prepared in advance to compensate for the lithium consumption that occurs during SEI formation and subsequent cycling, thereby preventing capacity loss without requiring excessive active lithium in the electrode materials themselves.
Solution Approach 2:
The patent changes the parameter of lithium content by adding a dedicated lithium foil layer with controlled thickness (0.1-5 μm) and lithium content (0.1-5 wt% relative to total electrode mass). This parameter adjustment provides additional lithium reservoir to offset the consumption from SEI formation, allowing the use of high-specific-capacity materials without sacrificing cycle life.
2Quantity of substance
If the positive electrode compacted density is increased to improve energy density, then the quantity of active material is improved, but the rate performance deteriorates due to reduced ion transport efficiency
Solution Approach 1:
The patent optimizes the compacted density parameter of the positive electrode to a specific range (3.8-4.2 g/cm³) that balances energy density and rate performance. Additionally, the introduction of lithium foil and optimization of electrode surface density (0.15-0.25 g/1540.25 mm²) create a balanced lithium distribution that facilitates ion transport while maintaining high energy density.
Solution Approach 2:
The patent creates a composite electrode structure combining the positive electrode material layer with a lithium foil layer. This composite structure allows the positive electrode to operate at optimized compacted density for energy density while the lithium foil provides additional lithium reservoir and ion transport pathways that maintain rate performance.
3Quantity of substance
If the positive electrode surface density is increased to improve energy density, then the quantity of active material is improved, but the cycle life deteriorates due to increased stress and structural degradation
Solution Approach 1:
The patent optimizes the surface density parameter to a specific range (0.15-0.25 g/1540.25 mm²) that balances energy density and structural stability. This parameter optimization prevents excessive stress on the electrode structure during cycling while maintaining high energy density through efficient space utilization.
Solution Approach 2:
The lithium foil layer is introduced as a preliminary compensation mechanism that provides additional lithium reservoir before cycling begins. This preliminary lithium source compensates for the lithium consumption that would otherwise occur due to SEI formation and structural degradation, thereby extending cycle life even at higher surface densities.
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 combination improves the cycle life and rate performance of lithium-ion batteries by reducing active lithium loss and maintaining structural stability, while the LiF-rich SEI film inhibits continuous loss, resulting in high energy density and prolonged battery life.
Implementation Method 1
the electrolyte includes fluoroethylene carbonate, where based on a total mass of the electrolyte, a percentage of fluoroethylene carbonate is 1% to 15%
Implementation Method 2
a second positive electrode material shown in Formula (II)
Data Source
AI summary
A lithium-ion secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a first positive electrode material and a second positive electrode material. The first positive electrode material has good cycling stability and high initial coulombic efficiency, and the second positive electrode material has a high initial charge specific capacity and low initial coulombic efficiency. This can compensate for the active lithium loss caused by the formation of SEI. The lithium-ion secondary battery provided in this application has advantages of good rate performance and long cycle life.