Positive Electrode Conductive Agent for High-Voltage Secondary Batteries
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Solution Overview
Problem
Secondary batteries with high-voltage positive electrode active materials experience unintended anion insertion and detachment during charging and discharging, leading to expansion and contraction of crystalline carbon materials, which can cause the positive electrode active material layer to detach from the current collector, resulting in poor charge-discharge characteristics.
Innovation Solution
A positive electrode for secondary batteries is designed with a positive electrode active material layer containing a combination of amorphous carbon and crystalline carbon materials, where the amorphous carbon has a specific surface area between 50 m2/g and 100 m2/g and a content between 0.5% and 5% by mass, and the crystalline carbon has an interplanar spacing of 0.340 nm or more, and a specific surface area between 1 m2/g and 5 m2/g, to prevent detachment and enhance conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a high-voltage positive electrode active material (operating voltage 4.5 V or more) is used to achieve higher energy density, then the energy density is improved, but unintended anion insertion and detachment occurs during charging and discharging, causing expansion and contraction of crystalline carbon materials, which can lead to detachment of the positive electrode active material layer from the current collector and poor charge-discharge characteristics
Solution Approach 1:
The patent changes the physical and chemical parameters of the carbon material by controlling its crystallinity and specific surface area. The crystalline carbon material is specified to have a specific surface area of 1 m²/g to 5 m²/g, which is significantly lower than conventional carbon materials. This parameter change reduces the total surface area available for anion insertion, thereby suppressing expansion and contraction while maintaining electrical conductivity necessary for high energy density operation
Solution Approach 2:
The patent employs a composite material approach by combining crystalline carbon material with specific properties (low specific surface area, controlled crystallinity) with the positive electrode active material. This composite structure allows the carbon material to serve dual functions: maintaining electrical conductivity and suppressing harmful anion insertion effects, thus enabling both high energy density and reliable charge-discharge characteristics
2Reliability
If the specific surface area of carbon material is increased to improve conductivity, then the conductivity is improved, but the contact area increases, leading to more significant expansion and contraction during anion insertion and detachment
Solution Approach 1:
The patent achieves the optimal balance between conductivity and stability by precisely controlling the specific surface area parameter of the crystalline carbon material to be 1 m²/g to 5 m²/g. This parameter optimization ensures sufficient electrical conductivity for battery operation while minimizing the surface area available for anion insertion, thereby reducing expansion and contraction and maintaining structural stability during charge-discharge cycles
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
This configuration improves charge-discharge characteristics by reducing the likelihood of detachment and suppressing electrolyte decomposition, leading to increased conductivity and prolonged battery life.
Implementation Method 1
the positive electrode conductive agent contains an amorphous carbon material and a crystalline carbon material... leading to increased conductivity
Implementation Method 2
an unintended phenomenon occurs in which an anion is inserted between layers of a crystalline carbon material during the charging and the anion is detached from the layers during discharging. This anion is a hexafluorophosphate ion (PF6−) when an electrolyte salt contained in an electrolyte is lithium hexafluorophosphate (LiPF6). In this case, the crystalline carbon material repeats expansion and contraction during charging and discharging
Data Source
AI summary
Provided is a secondary battery capable of improving charge-discharge characteristics. A positive electrode active material layer of a positive electrode has a positive electrode active material and a positive electrode conductive agent. The positive electrode active material is a high-voltage operating positive electrode material whose operating voltage is equal to or more than 4.5 V on a lithium metal basis. The positive electrode conductive agent contains an amorphous carbon material and a crystalline carbon material, and an interplanar spacing for lattice plane (002), a specific surface area, and a content in the positive electrode active material layer, thereof are so normalized as to be in predetermined ranges, respectively.