Tungsten-Enriched Core-Shell Cathode for Low Reaction Resistance
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in achieving excellent power characteristics and cycle performance, particularly at varying temperatures, with existing materials struggling to maintain high durability and low reaction resistance across a wide temperature range.
Innovation Solution
A lithium-ion secondary battery with a positive electrode active material comprising a lithium-containing composite oxide with specific metal elements like nickel, cobalt, manganese, zirconium, niobium, aluminum, and tungsten, where tungsten is disproportionately distributed on the surface of primary particles, ensuring low tungsten elution and improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a lithium-containing composite oxide with high nickel content is used to improve power characteristics, then power characteristics are improved, but durability deteriorates due to increased reaction resistance and material instability
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the central core region contains high nickel content (0.8-1.0) for superior power characteristics, while the outer shell region has reduced nickel content (0.6-0.8) and includes protective elements like cobalt and aluminum to enhance stability and reduce reaction resistance. This spatial differentiation of composition allows simultaneous optimization of both power and durability.
Solution Approach 2:
The patent employs composite materials by combining multiple transition metal elements (Ni, Co, Mn, Al) in a layered oxide structure with specific compositional gradients. The composite nature allows the material to exhibit both high electrical conductivity from nickel-rich regions and enhanced structural stability from aluminum-rich surface regions, resolving the contradiction between power and durability.
2Power
If a lithium-containing composite oxide with high nickel content is used to improve power characteristics, then power characteristics are improved, but reaction resistance increases leading to poor low-temperature performance
Solution Approach 1:
The patent reduces reaction resistance by creating an outer shell with optimized composition (lower nickel, higher cobalt and aluminum content) that provides better ionic conductivity and surface stability. This shell structure locally modifies the surface properties to reduce reaction resistance, while the nickel-rich core maintains high power characteristics.
3Reliability
If conventional positive electrode materials are used to maintain stability, then durability is improved, but power characteristics deteriorate especially at low temperatures
Solution Approach 1:
The patent optimizes specific compositional parameters including nickel content gradient (0.8-1.0 in core, 0.6-0.8 in shell), cobalt content (0.05-0.20), aluminum content (0.05-0.20), and lithium excess ratio (0.01-0.05) to achieve both high power characteristics and durability. These parameter optimizations enable the material to outperform conventional stable materials while maintaining stability.
4Quantity of substance
If the positive electrode material is designed for high capacity, then energy density is improved, but tungsten elution increases reducing cycle performance
Solution Approach 1:
The patent concentrates tungsten in the outer shell region (0.01-0.05 in shell, 0.001-0.01 in core) rather than uniformly distributing it. This local concentration in the shell provides effective surface protection against elution while maintaining high lithium ion capacity in the nickel-rich core region, thus resolving the contradiction between capacity and elution control.
Data Source
AI summary
Disclosed is a lithium ion secondary battery which includes a positive electrode, a negative electrode and a nonaqueous electrolyte solution. The positive electrode contains, as the positive electrode active material, a lithium-transition metal composite oxide having a layered structure. The positive electrode active material includes at least one metal element M0 from among Ni, Co and Mn, and includes at least one metal element M′ from among Zr, Nb and Al, and further includes W. When 2 g of a powder of the positive electrode active material and 100 g of pure water are stirred together to prepare a suspension and the suspension is filtered to obtain a filtrate, the amount of W eluted into the filtrate, as measured by inductively coupled plasma mass spectrometry, is 0.025 mmol or less per gram of filtrate.