Gradient Cathode Composition for High-Voltage Cycle Stability
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Solution Overview
Problem
Nickel-based cathode materials for lithium-ion batteries face structural instability and capacity decay due to parasitic side reactions and transition metal dissolution, especially at high voltage states, limiting their energy density and cyclability.
Innovation Solution
A cathode active material with a composite structure featuring a concentration gradient, where the core composition includes Ni, Mn, and Co, and the surface composition is predominantly Co with optional Ni and Mn, forming a rock-salt or disordered rock-salt phase, which helps in stabilizing the structure and enhancing energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high nickel content is used in cathode materials to achieve high capacity and high power, then energy density is improved, but structural instability increases leading to fast capacity decay and low thermal-abuse tolerance
Solution Approach 1:
The patent applies local quality by creating a concentration gradient structure where the nickel content varies spatially within the particle. The core region has high nickel content (0.8-1.0) for high capacity, while the surface region has reduced nickel content (0.3-0.6) for structural stability. This spatial variation in composition allows simultaneous optimization of energy density and cyclability.
Solution Approach 2:
The patent creates a composite structure with distinct core and surface regions having different compositions. The core consists of high-nickel NMC material for high capacity, while the surface forms a protective layer with lower nickel and higher cobalt/manganese content. This composite architecture combines the advantages of high-nickel materials (high capacity) with low-nickel materials (structural stability).
2Use of energy by moving object
If high voltage operation is implemented to improve energy density, then capacity is increased, but parasitic side reactions and transition metal dissolution accelerate causing capacity decay
Solution Approach 1:
The patent introduces a surface layer with modified composition as an intermediary between the high-nickel core and the electrolyte. This surface layer acts as a protective barrier that reduces direct contact between the reactive high-nickel material and the electrolyte, thereby suppressing parasitic side reactions and transition metal dissolution during high voltage operation.
Solution Approach 2:
The surface region is specifically engineered with different chemical properties (lower nickel, higher cobalt/manganese) compared to the core, creating local quality variation. This compositional differentiation at the surface provides enhanced chemical stability and resistance to electrolyte decomposition, enabling safe high voltage operation.
Data Source
AI summary
A cathode active material includes a composition expressed as:Li1+β(NixMnyCoz)M1α(Nix′Mny′Coz′)M21−αO2; orNa1+β(NixMnyCoz)M1α(Nix′Mny′Coz′)M21−αO2;where: M1 represents a core composition comprising of Ni, Mn, and/or Co or a combination of at two of thereof; M2 represents a surface composition having at least 50% Co, and, optionally Ni and/or Mn; the structure of M2 may be a composite structure and includes a rock-salt or disordered rock-salt phase; 0.5≤α<1, 0≤x≤1, 0≤y≤0.5, 0≤z≤1, 0≤x′≤0.5, 0≤y′≤0.5, 0.5≤z′≤1, and −0.1≤β≤0.1; the sum of x, y and z is 0.9-1.1, and the sum of x′, y′ and z′ is 0.9-1.1.