Lithium Ion Battery Negative Electrode Surface Area Optimization
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in maintaining high capacity retention when exposed to broad temperature conditions and experiencing repeated high-rate charging, as these properties are generally contradictory, making it difficult to achieve both high capacity retention and low internal resistance simultaneously.
Innovation Solution
A lithium ion secondary battery design featuring a negative electrode mixture layer with a specific surface area and pore volume configuration, where the product of the negative electrode active material reaction surface area and the number of lithium ions per unit battery capacity falls within a specific range (1 × 10^22 to 2.5 × 10^22 ions·m^2), ensuring high capacity retention at high temperatures and suppressing internal resistance rise during low-temperature high-rate charging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the negative electrode active material reaction surface area is increased to improve high-rate charging characteristics, then low-temperature high-rate charging performance is improved, but capacity retention at high temperature deteriorates
Solution Approach 1:
The invention optimizes the product of the negative electrode active material reaction surface area (S) and the number of lithium ions per unit battery capacity (N) to fall within a specific range (1×10^22 to 2.5×10^22 ions·m^2). This parameter optimization simultaneously achieves high-rate charging capability and high capacity retention, resolving the contradiction between improving productivity and maintaining reliability.
2Reliability
If the battery is designed for high capacity retention at high temperature, then storage stability is improved, but low-temperature high-rate charging performance deteriorates
Solution Approach 1:
By precisely controlling the product SN (reaction surface area × number of lithium ions per unit capacity) within the range of 1×10^22 to 2.5×10^22 ions·m^2, the invention achieves a balanced electrode structure that provides sufficient reaction sites for high-rate charging while maintaining appropriate lithium ion density for high capacity retention, thus resolving the contradiction between reliability and productivity.
3Productivity
If the negative electrode mixture layer pore volume is increased to improve lithium ion transport, then high-rate charging is enhanced, but internal resistance increases at low temperature
Solution Approach 1:
The invention optimizes the pore volume of the negative electrode mixture layer to 0.25 mL/cm^3 or less while controlling the product SN within 1×10^22 to 2.5×10^22 ions·m^2. This optimization ensures sufficient lithium ion transport pathways for high-rate charging while maintaining appropriate electrode density to prevent excessive internal resistance increase at low temperatures, resolving the contradiction between productivity and harmful factors.
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 high capacity retention at elevated temperatures and significantly reduces internal resistance increase during charge-discharge cycling at low temperatures, particularly effective for vehicular power supplies that encounter varying temperature conditions.
Implementation Method 1
The product of the negative electrode active material reaction surface area and the number of lithium ions per unit battery capacity falls within a specific range (1 × 10^22 to 2.5 × 10^22 ions·m^2)
Data Source
Figure 1~2
Figure 3~4
AI summary
The present invention provides a lithium ion secondary battery in which an electrode assembly, in which a positive electrode sheet having a positive electrode mixture layer and a negative electrode sheet having a negative electrode mixture layer are overlain each other, is housed in a container together with a nonaqueous electrolyte solution. The negative electrode mixture layer includes a carbon material having at least in part a graphite structure as a negative active material. When S (m2) represents a value obtained by calculating a total surface area of the negative electrode active material included in a region of the negative electrode mixture layer lying opposite the positive electrode mixture layer per 1 Ah of capacity of the battery, V represents a value obtained by calculating a total volume of pores included in the region of the negative electrode mixture layer per 1 Ah of capacity of the battery, and N represents the number of lithium ions included within the volume V of the nonaqueous electrolyte solution, the value α computed by the formula α = S × N is from 1 × 1025 to 2.5 × 1025.