Sintered Lithium Battery Cathode with Conductive Bonding Layer
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Solution Overview
Problem
Lithium secondary batteries with sintered lithium composite oxide cathodes face issues of low capacity and impaired cyclic characteristics due to grain boundary cracking and bonding interface separation caused by crystal lattice expansion/contraction during charge-discharge cycles, leading to reduced capacity and poor cycle retention.
Innovation Solution
A lithium secondary battery cathode configuration featuring a sintered lithium composite oxide sheet with a thickness of 30 μm or more, a mean pore size of 0.1 to 5 μm, and a voidage of 3% to 15%, bonded to a conductive collector via a conductive bonding layer, which reduces stress and enhances bonding strength to prevent cracking and separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the sintered sheet has a high lithium composite oxide filling ratio, then capacity is improved, but cyclic characteristic is impaired
Solution Approach 1:
The patent introduces a controlled porous structure in the sintered lithium composite oxide sheet with specific pore size (0.1 to 5 μm) and voidage (3% to 15%). This porous structure allows the material to accommodate crystal lattice expansion and contraction during charge-discharge cycles, preventing grain boundary cracks while maintaining high filling ratio and capacity.
Solution Approach 2:
The patent optimizes specific parameters including pore size (0.1 to 5 μm), voidage (3% to 15%), and thickness (30 μm or more) of the sintered sheet. By carefully controlling these parameters, the sheet achieves both high capacity and excellent cyclic characteristic, resolving the contradiction between filling ratio and cycle retention.
2Quantity of substance
If the sintered sheet has a thickness of 30 μm or more, then capacity is improved, but grain boundary cracking occurs
Solution Approach 1:
The porous structure with controlled pore size and distribution acts as a stress buffer that accommodates crystal lattice changes during lithium ion insertion and extraction. This prevents stress concentration at grain boundaries, eliminating cracking issues in thick sheets while maintaining high capacity.
Solution Approach 2:
The sintering process creates a pre-formed porous network structure before battery operation. This preliminary porous structure is designed to accommodate future expansion and contraction, preventing crack formation during actual charge-discharge cycles in thick sheets.
3Reliability
If the sintered sheet has high voidage, then cyclic characteristic is improved, but capacity is reduced
Solution Approach 1:
The patent precisely controls the voidage parameter within the range of 3% to 15%, which is sufficient to accommodate crystal lattice changes and prevent cracks, yet low enough to maintain high filling ratio and capacity. This optimized parameter range resolves the contradiction between cycle retention and capacity.
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 configuration enhances the battery's capacity and maintains excellent cycle characteristics by effectively releasing stress and improving bonding strength, preventing grain boundary cracking and bonding interface separation.
Implementation Method 1
crystal lattice expansion/contraction associated with intercalation and deintercalation of lithium ions in charge-discharge cycles
Data Source
AI summary
To provide a lithium secondary battery which has high capacity while maintaining excellent cycle characteristic. The lithium secondary battery cathode of the present invention includes a cathode collector formed of a conductive substance, and a cathode active material layer formed of a sintered lithium composite oxide sheet. The cathode active material layer is bonded to the cathode collector by the mediation of a conductive bonding layer. A characteristic feature of the present invention resides in that the cathode active material layer has a thickness of 30 μm or more, a mean pore size of 0.1 to 5 μm, and a voidage of 3% or more and less than 15%.