Lithium Secondary Battery Electrode Balance Against Low-Temperature Li Plating
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Solution Overview
Problem
Lithium secondary batteries face challenges in achieving high energy density while maintaining stability and lifespan at low temperatures due to increased internal resistance and Li plating, particularly when reducing conductive materials to enhance active material content.
Innovation Solution
A lithium secondary battery design with a specific CFC ratio of 0.38 to 1.962, involving a balanced weight ratio of negative electrode conductive material, particle size of active materials, and N/P ratio, using graphite-based negative electrodes and single particle type lithium nickel-based oxides with low nickel content for positive electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the content of conductive materials is reduced to increase active material content, then energy density is improved, but electrical conductivity decreases and internal resistance increases
Solution Approach 1:
The patent optimizes the weight ratio of conductive material to active material within a specific range (0.01-0.05) to achieve the best balance between energy density and electrical conductivity. This parameter optimization allows maximizing active material content while maintaining sufficient conductivity
Solution Approach 2:
The patent uses composite conductive materials comprising multiple components (e.g., carbon black, acetylene black, and conductive polymer) to enhance electrical conductivity while using minimal amounts, thereby maintaining high energy density without sacrificing conductivity
2Quantity of substance
If the content of conductive materials is reduced to increase active material content, then energy density is improved, but Li plating occurs at low temperatures
Solution Approach 1:
The patent optimizes the CFC value (a composite parameter involving conductive material weight ratio, active material particle size, loading amount, and N/P ratio) to a specific range to prevent Li plating at low temperatures while maintaining high energy density
Solution Approach 2:
The patent incorporates sufficient conductive material in advance to ensure adequate electrical conductivity at low temperatures, preventing Li plating before it can occur during battery operation
3Quantity of substance
If high voltage operation is implemented to achieve high energy density, then energy density is improved, but lifespan characteristics at low temperatures deteriorate
Solution Approach 1:
The patent optimizes multiple parameters simultaneously including conductive material weight ratio (0.01-0.05), active material particle size (D50: 5-20 μm), loading amount (0.2-0.5 g/25 cm²), and N/P ratio (1.05-1.10) to achieve high energy density while maintaining excellent low-temperature lifespan
Solution Approach 2:
The patent incorporates sufficient conductive material and optimizes electrode structure in advance to cushion against the increased internal resistance and Li plating tendencies that occur at high voltage and low temperatures, preventing degradation before it happens
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 design enhances lithium mobility, reduces electrode resistance, and prevents Li plating, resulting in improved lifespan and energy density, especially at low temperatures, with a charge cut-off voltage of 4.35 V or greater and energy density of 260 Wh/kg or more.
Implementation Method 1
a negative electrode conductive material... enhances lithium mobility, reduces electrode resistance
Implementation Method 2
CFC defined by Equation 1 below is 0.38 to 1.962... prevents Li plating
Data Source
AI summary
Provided is a lithium secondary battery including a negative electrode including a negative electrode composite layer including a negative electrode active material including a first negative electrode active material and a second negative electrode active material, a negative electrode conductive material, and a negative electrode binder; a positive electrode including a positive electrode composite layer including a positive electrode active material, a positive electrode conductive material, and a positive electrode binder; and an electrolyte, and CFC defined by Equation 1 is 0.38 to 1.962:CFC=100×Wc−{(D50,a1×D50,a2×L×RN/P×1010)/MWc} Equation 1:wherein in Equation 1, all the variables are described herein.