Lithium-Ion Cathode Layer Structure to Prevent Particle Cracking
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Solution Overview
Problem
Conventional lithium ion secondary batteries face issues with increased internal resistance and decreased capacity due to cracking of positive electrode active material particles caused by high intercalation and deintercalation of lithium ions, particularly in layers with smaller average particle diameters.
Innovation Solution
The lithium ion secondary battery design includes a positive electrode with a superficial layer containing larger average particle diameter active material particles and a lower space ratio, opposed to a negative electrode via a separator, and a deep layer with smaller average particle diameter active material particles, providing a shield effect to enhance durability and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If smaller average particle diameter positive electrode active material particles are used in the upper layer to decrease lithium ion diffusion resistance, then battery capacity is improved, but particle cracking occurs due to high intercalation and deintercalation of lithium ions
Solution Approach 1:
The patent applies local quality by creating a gradient structure where the upper layer contains larger particle diameter positive electrode active material particles that are more resistant to cracking, while the lower layer contains smaller particle diameter particles that provide lower diffusion resistance. This spatial differentiation of particle sizes allows each layer to fulfill its specific function: the upper layer maintains structural integrity during high intercalation/deintercalation cycles, while the lower layer ensures efficient lithium ion transport and high battery capacity.
2Power
If smaller average particle diameter particles are placed in the upper layer to reduce diffusion resistance, then internal resistance decreases, but durability deteriorates due to particle cracking
Solution Approach 1:
The patent implements local quality by assigning different particle size characteristics to different spatial locations within the positive electrode. The upper layer utilizes larger particle diameter particles that exhibit superior mechanical strength and resistance to cracking during repeated charge/discharge cycles, thereby ensuring long-term durability. Meanwhile, the lower layer employs smaller particle diameter particles that facilitate rapid lithium ion diffusion, resulting in lower internal resistance and improved power performance. This localized optimization of particle size distribution resolves the contradiction between power and durability.
3Duration of action of stationary object
If larger average particle diameter particles are used in the superficial layer to prevent cracking, then durability is improved, but lithium ion diffusion resistance increases
Solution Approach 1:
The patent applies local quality by strategically positioning larger average particle diameter positive electrode active material particles in the upper layer (superficial layer) that directly faces the negative electrode through the separator. This location experiences the highest intercalation and deintercalation activity, making it susceptible to particle cracking. The larger particles in this critical region provide enhanced mechanical stability and prevent cracking, thereby improving battery durability. Simultaneously, the lower layer contains smaller particle diameter particles that ensure efficient lithium ion diffusion pathways, maintaining low diffusion resistance and high power performance. This spatially differentiated particle size distribution effectively resolves the contradiction between durability and power.
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 design suppresses cracking of positive electrode particles, maintains battery capacity, and improves durability, enabling higher output power and extended discharge duration, suitable for electric vehicle applications.
Implementation Method 1
the positive electrode active material layer in the upper layer of the positive electrode plate opposing the negative electrode plate via the separator increases in intercalation and deintercalation of lithium ions due to charge/discharge reaction of the battery
Implementation Method 2
the lithium ion diffusion resistance can be decreased in the upper layer of the positive electrode plate
Data Source
AI summary
A lithium ion secondary battery with increased durability and capacity includes a positive electrode, a negative electrode, and a separator. The positive electrode includes a current collector foil and an electrode mixture layer disposed on a surface of the current collector foil. The positive electrode mixture layer includes a superficial layer portion and a deep layer portion. The superficial layer portion opposes the negative electrode via the separator. The deep layer portion is disposed between the superficial layer portion and the current collector foil. The superficial layer portion contains positive electrode active material particles having an average particle diameter larger than an average particle diameter of positive electrode active material particles contained in the deep layer portion. A space ratio between the positive electrode active material particles in the superficial layer portion is lower than a space ratio between the positive electrode active material particles in the deep layer portion.