Inorganic Phosphate Coating for High-Voltage Battery Endurance
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries with high energy density face challenges in maintaining endurance and electron conductivity when the operation upper limit potential of the positive electrode is set to 4.3 V or more, due to increased internal resistance caused by low electron conductivity of lithium-ion conductive glass coatings.
Innovation Solution
Incorporating an inorganic phosphate compound with ion conductivity into the positive electrode, which suppresses decomposition reactions, traps hydrofluoric acid, and forms a stable film with low resistance, while reducing the ratio of coarse particles to enhance electron conductivity and form a preferable conductive path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the operation upper limit potential of the positive electrode is set to 4.3 V or more, then high energy density can be achieved, but the internal resistance increases and endurance deteriorates
Solution Approach 1:
The patent changes the particle size parameter of the inorganic phosphate compound to resolve the contradiction. By controlling the particle size to 20 μm or less, the patent achieves both high energy density (through effective coating at high potential 4.3V or more) and high endurance (through reduced internal resistance from fine particle distribution). This parameter optimization allows the coating to function effectively without causing the internal resistance increase that would normally accompany high potential operation.
Solution Approach 2:
The patent uses a composite structure combining the positive electrode active material with an inorganic phosphate compound coating. This composite approach allows the inorganic phosphate compound to suppress decomposition reactions and trap hydrofluoric acid at the high operating potential of 4.3V or more, thereby protecting the active material and maintaining both high energy density and excellent endurance without the internal resistance penalties of conventional coatings.
2Reliability
If lithium-ion conductive glass is used to suppress decomposition reactions, then battery swelling is reduced, but electron conductivity decreases and internal resistance increases
Solution Approach 1:
The patent changes the material parameter from conventional lithium-ion conductive glass to a specific inorganic phosphate compound with controlled particle size (20 μm or less). This parameter change enables the coating to maintain electron conductivity while providing decomposition suppression, thereby reducing internal resistance compared to conventional glass coatings while still protecting against electrolyte decomposition at high potential.
Solution Approach 2:
The patent applies the inorganic phosphate compound coating with specific local properties (fine particle size distribution) to the positive electrode active material surface. This localized coating with optimized particle size provides decomposition suppression and hydrofluoric acid trapping exactly where needed, while the fine particle distribution ensures good electron conductivity is maintained throughout the electrode structure, avoiding the internal resistance increase associated with coarser conventional glass coatings.
3Stability of the object's composition
If coarse particles of inorganic phosphate compound are used, then coating coverage is improved, but electron conductivity decreases due to poor conductive path formation
Solution Approach 1:
The patent optimizes the particle size parameter of the inorganic phosphate compound to 20 μm or less. This parameter optimization achieves both adequate coating coverage and excellent electron conductivity by creating a fine particle distribution that forms continuous conductive paths throughout the positive electrode active material, eliminating the internal resistance issues associated with coarse particle coatings.
Solution Approach 2:
The patent achieves homogeneous distribution of fine inorganic phosphate compound particles throughout the positive electrode active material. This homogeneous fine particle distribution ensures uniform coating coverage while maintaining excellent electron conductivity throughout the electrode, creating consistent conductive paths that avoid the localized resistance issues caused by coarse particle aggregation.
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
This approach enables a nonaqueous electrolyte secondary battery with high energy density, excellent input/output characteristics, and improved endurance, suitable for applications in hybrid and electric vehicles by maintaining low internal resistance and preventing element elution from the positive electrode active material.
Implementation Method 1
A decomposition reaction of a nonaqueous electrolyte in a high potential state can be suppressed
Implementation Method 2
Hydrofluoric acid (HF) generated by the hydrolysis reaction of the supporting salt (for example, LiPF6) is trapped in the inorganic phosphate compound and the acidity of the nonaqueous electrolyte can be alleviated thereby
Implementation Method 3
a film that is stable and has relatively low resistance. (a film that contains LiF, for example) can be formed on a surface of the positive electrode active material
Data Source
AI summary
According to the present invention, a nonaqueous electrolyte secondary battery that includes a positive electrode, a negative electrode and a nonaqueous electrolyte is provided. The positive electrode has an operation upper limit potential of 4.3 V or more based on metal lithium and includes a positive electrode active material and an inorganic phosphate compound that has ion conductivity. The inorganic phosphate compound is in a particle state. A ratio of particles having a particle size of 20 μm or more is 1% by volume or less when an entirety of the inorganic phosphate compound is set to 100% by volume. Further, a ratio of particles having a particle size of 10 μm or more may be 10% by volume or less when an entirety of the inorganic phosphate compound is set to 100% by volume.