Li-Co-O Positive Electrode Material for High-Voltage Cycle Stability
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges in achieving high capacity, excellent charging and discharging cycle performance, and preventing the elution of transition metals like cobalt, especially when subjected to high voltage for extended periods, which affects their stability and safety.
Innovation Solution
A positive electrode active material composed of lithium, cobalt, and oxygen, with magnesium and fluorine, having a specific spin density and lattice constants, is developed to inhibit cobalt elution and maintain structural stability during charging and discharging cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high voltage charging is applied to increase capacity, then energy density is improved, but cobalt elution increases and structural stability deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the positive electrode material by incorporating magnesium and fluorine elements, and controlling the oxidation states of cobalt (Co3+ and Co4+), to achieve a balance between high voltage charging capability and cobalt elution resistance. This allows the material to maintain structural stability while achieving high energy density.
Solution Approach 2:
The patent creates a composite material system by combining lithium cobalt oxide with magnesium and fluorine elements, forming a multi-element composite structure that synergistically improves both the voltage characteristics and the resistance to cobalt elution, resolving the contradiction between energy density and reliability.
2Quantity of substance
If charging and discharging cycles are extended to improve capacity utilization, then energy storage is improved, but capacity degradation increases due to cobalt elution
Solution Approach 1:
The patent modifies the material composition parameters by adding magnesium and fluorine, and controlling the Co3+/Co4+ ratio, to enhance the structural stability during repeated charging and discharging cycles. This enables the material to maintain its capacity over extended cycling periods without significant degradation from cobalt elution.
3Power
If high voltage charging state is maintained to maximize energy output, then power is improved, but cobalt elution accelerates and safety decreases
Solution Approach 1:
The patent introduces magnesium and fluorine elements as intermediary components that mediate between the high voltage charging state and the cobalt lattice structure. These intermediaries stabilize the structure under high voltage conditions, preventing cobalt elution while maintaining high energy output capability.
Solution Approach 2:
The patent adjusts the oxidation state parameters of cobalt and the compositional parameters of magnesium and fluorine to create a material that can sustain high voltage charging states without accelerating cobalt elution, thus maintaining both power output and safety.
Data Source
AI summary
A positive electrode active material with high capacity and excellent charging and discharging cycle performance for a lithium-ion secondary battery is provided. The positive electrode active material contains lithium, cobalt, and oxygen, and the spin density attributed to a bivalent cobalt ion and a tetravalent cobalt ion is within a predetermined range. It is preferable that the positive electrode active material further contain magnesium. An appropriate magnesium concentration is represented as a concentration with respect to cobalt. It is also preferable that the positive electrode active material further contain fluorine.