Lithium Titanate Negative Electrode Surface Modification
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Solution Overview
Problem
Nonaqueous electrolyte batteries using lithium titanate as a negative electrode face safety issues due to over-insertion of Li during overcharge, leading to sudden potential drops and heat generation, which can cause thermal instability.
Innovation Solution
A nonaqueous electrolyte battery design with a negative electrode having a spinel-type lithium titanate surface where the Li atom abundance ratio to Ti atom abundance ratio (A Li/A Ti) is increased between 0.002 to 0.02 per charge-and-discharge cycle, inhibiting over-insertion of Li and preventing sudden potential drops through the formation of a lithium-containing compound layer, which can include rock salt-type lithium titanate, preventing excessive insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium titanate is used as negative electrode active material, then safety against internal short-circuit is improved, but over-insertion of Li during overcharge causes reduction reaction and sudden heat generation
Solution Approach 1:
A lithium-containing compound layer is introduced as an intermediary between the lithium titanate particles and the electrolyte. This layer acts as a mediator that prevents direct contact and reduction reactions during overcharge, while still allowing lithium ion insertion/extraction during normal operation. The compound layer specifically suppresses harmful reduction reactions at the particle surface without blocking beneficial lithium ion transport.
Solution Approach 2:
The invention changes the chemical composition and surface properties of the lithium titanate particles by forming a lithium-containing compound layer on the surface. This parameter change in surface composition prevents over-insertion of Li and suppresses reduction reactions during overcharge, while maintaining the spinel structure's ability to accommodate lithium ions during normal charge-discharge cycles.
2Reliability
If lithium titanate surface is modified to prevent Li over-insertion, then safety is improved, but lithium ion insertion/extraction efficiency may be reduced
Solution Approach 1:
The lithium-containing compound layer is formed locally on the surface of lithium titanate particles, creating a differentiated structure where the core maintains high lithium ion conductivity and the surface provides protective functionality. This local modification ensures that the bulk material's excellent electrochemical properties are preserved while adding surface-level protection against over-insertion and reduction reactions.
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 design effectively prevents Li over-insertion and potential drops during overcharge, enhancing safety by maintaining stable lithium distribution and preventing sudden heat generation, thus improving overall safety and performance.
Implementation Method 1
a negative electrode active material particles which includes a spinel-type lithium titanate
Implementation Method 2
the Li atom abundance ratio A Li and the Ti atom abundance ratio A Ti being obtained according to a photoelectron spectroscopic measurement for the surface of negative electrode mixture layer
Implementation Method 3
the formation of a lithium-containing compound layer, which can include rock salt-type lithium titanate, preventing excessive insulation
Data Source
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AI summary
According to an embodiment, a nonaqueous electrolyte battery is provided. The nonaqueous electrolyte includes a negative electrode, a positive electrode and a nonaqueous electrolyte. The negative electrode includes negative electrode active material particles. The negative electrode active material particles include a spinel-type lithium titanate. The negative electrode has such a surface state that a ratio ALi/ATi of an Li atom abundance ratio ALi to a Ti atom abundance ratio ATi, according to a photoelectron spectroscopic measurement for a surface, is increased at a rate of 0.002 to 0.02 per cycle in a charge-and-discharge cycle test. The charge-and-discharge cycle test is to be performed in a 45°C environment. The Li atom abundance ratio ALi is calculated from a peak derived from a Li 1s-orbital that appears in a binding energy region of 52 eV to 58 eV. The Ti atom abundance ratio ATi is calculated from a peak derived from a Ti 2p-orbital that appears in a binding energy region of 455 eV to 462 eV.