Layered Electroconductive Oxide Coating Orientation for Lithium Ion Battery
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Solution Overview
Problem
Lithium ion secondary cells face challenges in achieving high energy density and durability due to the anisotropy of electroconductivity in existing positive electrode active materials, leading to increased cell resistance and reduced durability from mismatched electroconductive directions and peeling of the electroconductive oxide coating.
Innovation Solution
A positive electrode active material with a lithium transition metal complex oxide base and a layered electroconductive oxide coating, where the stacking plane directions of both are matched to within an average angle of 60°, reducing anisotropy and stress accumulation during charge and discharge cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an electroconductive oxide with large anisotropy of electroconductivity is coated on the base active material, then thermal stability is improved, but cell resistance increases when the electroconductive directions are mismatched
Solution Approach 1:
The patent applies local quality by controlling the crystal orientation of the electroconductive oxide coating at the interface with the base active material. Specifically, the coating is designed to have its c-axis (high electroconductivity direction) oriented within 30 degrees of the a-b plane of the base material, creating a localized optimal electroconductive pathway at the critical interface region where charge transfer occurs.
Solution Approach 2:
The patent changes the orientation parameter of the electroconductive oxide coating by controlling the crystal growth direction during the coating process. By adjusting the orientation angle parameter (θ) to be within 30 degrees of the a-b plane, the electroconductivity in the charge transfer direction is maximized, thereby reducing cell resistance while maintaining thermal stability.
2Reliability
If an electroconductive oxide coating is applied to improve thermal stability, then thermal stability is improved, but the coating peels off due to base material expansion and contraction, reducing durability
Solution Approach 1:
The patent creates a localized stress-absorbing structure at the coating-base material interface by controlling the crystal orientation. The specific orientation (c-axis within 30 degrees of the a-b plane) creates a buffer zone that locally accommodates expansion and contraction stresses, preventing stress accumulation that would cause peeling while maintaining the coating's thermal stability function.
Solution Approach 2:
The patent applies beforehand cushioning by designing the crystal orientation of the coating to inherently accommodate future expansion and contraction stresses. The oriented structure acts as a pre-configured stress buffer that absorbs mechanical stresses before they can accumulate and cause coating peeling, thereby improving durability without sacrificing thermal stability.
3Reliability
If the electroconductive direction of the base material is not matched with the electroconductive direction of the coating, then thermal stability is maintained, but input-output characteristic deteriorates due to increased cell resistance
Solution Approach 1:
The patent applies local quality by creating an optimized electroconductive pathway at the critical interface region. The coating's c-axis is oriented within 30 degrees of the base material's a-b plane, establishing a localized high electroconductivity zone that facilitates efficient charge transfer while the rest of the coating maintains its thermal stability properties.
Solution Approach 2:
The patent changes the orientation parameter of the coating to optimize the electroconductive pathway. By setting the angle θ between the coating's c-axis and the base material's a-b plane to within 30 degrees, the electroconductivity in the charge transfer direction is maximized, improving input-output characteristics while maintaining thermal stability.
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 enhances electroconductivity, reduces cell resistance, and improves durability by maintaining the coating's adherence to the base material, resulting in superior input-output characteristics and long-term capacity retention.
Implementation Method 1
lithium ion secondary cell
Implementation Method 2
electroconductive oxide
Implementation Method 3
stresses are unlikely to be accumulated when the base portion expands and contracts
Implementation Method 4
lithium transition metal complex oxide having a layered crystal structure
Data Source
AI summary
The positive electrode active material disclosed herein includes a base portion including a lithium transition metal complex oxide having a layered crystal structure, and a coating portion including an electroconductive oxide having a layered crystal structure. A smaller angle θ formed by a stacking plane direction of the lithium transition metal complex oxide and a stacking plane direction of the electroconductive oxide satisfies the following conditions: an average angle θave. obtained by arithmetically averaging the angle θ satisfies 0°≤θave.≤60°; and a ratio of points in which the angle θ is greater than 60° is 39% or less.