Dual-Layer Coated Positive Electrode for Battery Resistance Stability
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face challenges in maintaining low initial resistance and preventing resistance increases during high temperature cycles, as existing methods fail to effectively suppress charge transfer resistance and side reactions at the positive electrode.
Innovation Solution
A nonaqueous electrolyte secondary battery design featuring a positive electrode active material with a lithium transition metal composite oxide coated with a lithium metal compound layer and a boron compound layer, forming a strong coating film that reduces charge transfer resistance and suppresses metal elution and side reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer coating (e.g., TiO2 or boric acid compound) is applied on the surface of lithium transition metal composite oxide, then manufacturing simplicity is maintained, but resistance increase during high temperature cycles cannot be suppressed
Solution Approach 1:
The coating is divided into two distinct layers: a first layer containing a compound of a predetermined element (Groups IV-VI) and a second layer containing a boric acid compound. This segmentation allows each layer to perform its specific function - the first layer provides structural stability and prevents metal elution, while the second layer suppresses side reactions and maintains low resistance during high temperature cycles.
Solution Approach 2:
The patent uses a composite coating structure combining two different material systems (predetermined element compound and boric acid compound) to achieve properties that neither material could provide alone. This composite approach enables simultaneous suppression of metal elution and side reactions, resolving the contradiction between reliability and complexity.
2Manufacturing precision
If the second layer is interposed between the lithium transition metal composite oxide and the first layer, then manufacturing flexibility is increased, but the first layer cannot be formed over the entire particle surface
Solution Approach 1:
The first layer is formed first on the surface of the lithium transition metal composite oxide particles, ensuring complete coverage before applying the second layer. This preliminary action guarantees that the entire particle surface is covered by the first layer, which is critical for preventing metal elution and maintaining structural integrity during subsequent processing and high temperature operation.
3Reliability
If existing single-layer coating methods are used, then charge transfer resistance can be reduced, but side reactions occur during high temperature cycles causing resistance increase
Solution Approach 1:
The coating is divided into two distinct layers: a first layer containing a compound of a predetermined element (Groups IV-VI) and a second layer containing a boric acid compound. This segmentation allows each layer to perform its specific function - the first layer provides structural stability and prevents metal elution, while the second layer suppresses side reactions and maintains low resistance during high temperature cycles.
Solution Approach 2:
The two-layer coating structure acts as an intermediary barrier between the lithium transition metal composite oxide and the electrolyte. The first layer serves as a primary protective barrier preventing metal elution, while the second layer acts as a secondary barrier suppressing side reactions. This dual-layer intermediary structure effectively eliminates the harmful effects of direct contact between the oxide and electrolyte during high temperature cycles.
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 battery exhibits suppressed resistance increase during high temperature cycles, maintaining low initial resistance and improving overall performance by preventing metal elution and side reactions at the positive electrode.
Implementation Method 1
a first layer composed of a lithium metal compound represented by a general formula of LixMyOz and formed on each particle surface of the lithium transition metal composite oxide; and a second layer composed of a boron compound and formed on the first layer
Implementation Method 2
the first layer is formed over the entire particle surface of the lithium transition metal composite oxide without the second layer being interposed therebetween... an increase in battery resistance during high temperature cycles can be suppressed
Data Source
AI summary
In a nonaqueous electrolyte secondary battery, a positive electrode contains a positive electrode active material A. The positive electrode active material A includes: a lithium transition metal composite oxide represented by a general formula of LiaNibCocMndAleMfOg (in the formula, M is at least one element selected from Groups IV, V, and VI, and 0.8≤a≤1.2, b≥0.82, 0<c≤0.08, 0.05≤d≤0.12, 0≤e≤0.05, 0.01≤f≤0.05, and 1≤g≤2 are satisfied) in the form of particles; a first layer composed of a lithium metal compound represented by a general formula of LixMyOz (in the formula, 1≤x≤4, 1≤y≤5, and 1≤z≤12 are satisfied) and formed on each particle surface of the lithium transition metal composite oxide; and a second layer composed of a boron compound and formed on the first layer. The first layer is formed over the entire particle surface of the lithium transition metal composite oxide without the second layer being interposed therebetween.