Co-Rich Cathode Coating for Low-Temperature Power and Cycle Life
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Solution Overview
Problem
Existing lithium-ion battery positive electrode materials face challenges in simultaneously improving low-temperature performance and high-temperature cycle life under high voltage, as measures to enhance kinetic performance often degrade cycle life and vice versa.
Innovation Solution
A positive electrode material is developed, comprising a matrix with a Co-rich first coating layer having both spinel and rock-salt phase structures. The Co-rich layer enhances lithium ion conductivity and reduces interface charge transfer impedance, while the dual phase structure improves surface stability and cycling performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the size of primary or secondary grains of material particles is reduced and specific surface area is increased to improve kinetic performance, then low-temperature performance and charge transfer impedance are improved, but high-temperature cycle life is shortened
Solution Approach 1:
The patent applies local quality by creating a Co-rich coating layer with spinel phase structure specifically on the surface of the positive electrode material particles. This surface-modified region has different properties (higher Co content, spinel phase) than the bulk material, providing improved kinetic performance at the surface while the bulk material maintains its original properties for long-term stability.
Solution Approach 2:
The patent creates a composite structure consisting of the original positive electrode material matrix combined with a Co-rich coating layer having spinel phase structure. This composite material combines the advantages of both components: the bulk material provides structural stability and capacity, while the spinel-phase coating layer provides enhanced ionic conductivity and surface stability.
2Quantity of substance
If the upper limit voltage is increased to improve energy density, then energy density is improved, but high-temperature cycle life is reduced due to material degradation
Solution Approach 1:
The patent applies preliminary action by pre-forming a Co-rich coating layer with spinel phase structure on the surface of the positive electrode material before battery assembly. This pre-established protective layer prevents material degradation when high voltage operation is subsequently applied, allowing the battery to operate at high voltages without suffering from the usual cycle life penalties.
3Duration of action of stationary object
If surface metal oxide coating is applied to improve cycle life under high voltage, then high-temperature cycle life is improved, but kinetic performance and charge transfer efficiency are degraded
Solution Approach 1:
The patent applies parameter changes by specifically controlling the Co content in the coating layer to be higher than in the bulk material (W1 > W2), and by controlling the coating layer to form a spinel phase structure. These parameter changes (composition and crystal phase) fundamentally alter the properties of the surface layer, providing both improved ionic conductivity for kinetic performance and structural stability for cycle life.
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 proposed positive electrode material effectively improves low-temperature performance by increasing the low-temperature valley voltage and reducing temperature rise during high-rate discharge, while also extending high-temperature cycle life under high voltage.
Implementation Method 1
reduce solid phase diffusion and charge transfer impedance
Implementation Method 2
increase lithium ion conductivity, interface charge transfer impedance of the material can be reduced
Data Source
AI summary
A positive electrode material, including: a matrix and a first coating layer located on surface of the matrix, where based a molar content of metal elements other than Li in the first coating layer, a molar percentage of element Co in the first coating layer is W1; and based on a molar content of metal elements other than Li in the matrix, a molar percentage of element Co in the matrix is W2, where W1>W2; and the first coating layer includes a first region having a spinel phase structure.