Positive Electrode Oxide Coating Gradient for Short-Circuit Safety
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Solution Overview
Problem
Existing secondary battery positive electrodes face issues with increased resistance due to coatings, which can lead to reduced safety during internal short circuits, particularly due to heat generation.
Innovation Solution
A positive electrode with a lithium-containing transition metal oxide active material layer, where an oxide film is formed with a specific thickness distribution to cover active material particles, using a gas phase containing a first element other than nonmetal elements, to maintain low resistance and enhance safety during internal short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an oxide film is formed on the surface of active material particles to suppress electrolyte decomposition, then battery safety is improved, but electrode resistance increases
Solution Approach 1:
The patent applies local quality by creating a non-uniform oxide film thickness distribution on active material particles. The film is thinner at the surface (0.1-5 nm) to minimize resistance and maintain conductivity, while being thicker near the current collector interface (0.5-20 nm) to provide enhanced safety protection. This spatial variation in film quality resolves the contradiction between safety improvement and resistance increase.
Solution Approach 2:
The patent changes the parameter of oxide film thickness from a uniform value to a gradient distribution. By controlling the thickness to decrease from the current collector side toward the particle surface, the system optimizes both safety (thicker film near interface) and electrical performance (thinner film at surface). This parameter transformation resolves the technical contradiction between competing requirements.
2Reliability
If the oxide film thickness is increased to improve safety during internal short circuits, then heat generation is reduced, but the resistance and short-circuit current increase
Solution Approach 1:
The patent uses local quality by positioning the thickest oxide film region (near the current collector interface) exactly where safety protection is most critical during internal short circuits. The thinner surface region maintains low resistance and limits short-circuit current, while the thicker interior region provides heat management and safety protection. This localized differentiation resolves the contradiction between safety improvement and short-circuit current increase.
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 solution effectively suppresses the increase in short-circuit current and resistance, improving safety while maintaining normal battery operation by controlling the oxide film thickness and presence probability across the electrode layer.
Implementation Method 1
an oxide film covering at least part of surfaces of the active material particles... a film formation step of, after the supporting step, exposing the active material particles to a gas phase containing a first element other than nonmetal elements, to form an oxide film
Data Source
AI summary
A positive electrode for a secondary battery including a positive electrode current collector, and a positive electrode active material layer supported on the positive electrode current collector. The positive electrode active material layer includes active material particles and an oxide film covering at least part of surfaces of the active material particles. The active material particles include a lithium-containing transition metal oxide, and the oxide film contains an oxide of a first element other than nonmetal elements. When a thickness of the positive electrode active material layer is denoted by TA, Tb>Tt is satisfied, where the Tb and the Tt are thicknesses of the oxide film at a position of 0.25TA and at a position of 0.75TA, respectively, from a surface of the positive electrode current collector in the positive electrode active material layer.