Positive Electrode Material with Sr2TiO4 Surface Layer for DC Resistance Control
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Solution Overview
Problem
Lithium-ion batteries experience a rapid increase in DC resistance during cycling, leading to voltage drops and automatic shutdowns, necessitating a positive electrode material that inhibits this increase without affecting cycle performance.
Innovation Solution
A positive electrode material comprising a lithium composite oxide with a surface layer of Sr2TiO4, Sr2SiO4, or Sr2TiO4, where strontium content decreases from the surface to the interior, reacting with HF to form SrF2, a super acid that cleans impurities without eroding the surface, and Si or Ti prevents electrolyte decomposition, maintaining low DC resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional positive electrode materials are used, then the battery can operate initially, but DC resistance increases rapidly during cycling causing voltage drops and shutdowns
Solution Approach 1:
A surface layer comprising Sr2TiO4, Sr2SiO4, or a mixture thereof is formed on the positive electrode material surface. This intermediate layer acts as a mediator that reacts with HF to form SrF2, which cleans insulating impurities (LiOH, Li2CO3) from the surface without eroding the active material, thereby maintaining low DC resistance during cycling while preserving cycle stability
Solution Approach 2:
The invention changes the chemical composition parameters of the surface layer by incorporating Sr-containing compounds (Sr2TiO4, Sr2SiO4) with specific ratios. The Sr content on the surface is controlled to be higher than in the interior, creating a gradient structure that optimizes HF reaction capability while preventing surface erosion, thus resolving the contradiction between reliability and resistance increase
2Object-affected harmful factors
If the surface layer reacts with HF to clean impurities, then DC resistance is maintained low, but the surface may be eroded
Solution Approach 1:
The invention converts the harmful effect of HF (which can erode the surface) into a beneficial cleaning mechanism. Sr in the surface layer reacts with HF to form SrF2, a super acid that selectively removes insulating impurities (LiOH, Li2CO3) from the surface without damaging the active material. This transforms HF from a surface-destroying agent into a surface-cleaning agent, maintaining both impurity removal and surface integrity
3Reliability
If Si or Ti is used to prevent electrolyte decomposition, then cycle stability improves, but manufacturing complexity increases
Solution Approach 1:
The invention uses composite materials Sr2TiO4 and Sr2SiO4 that combine multiple functions in a single surface layer formulation. These compounds simultaneously provide HF reaction capability (for impurity removal), surface protection, and electrolyte decomposition prevention. The sol-gel process allows these composite materials to be applied as simple aqueous solutions, reducing manufacturing complexity despite the advanced functionality provided
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 significantly slows the increase in DC resistance during cycles while maintaining high cycle stability and capacity, ensuring the lithium-ion battery's performance is not compromised.
Implementation Method 1
reacting with HF to form SrF2, a super acid that cleans impurities without eroding the surface
Implementation Method 2
Si or Ti prevents electrolyte decomposition, maintaining low DC resistance
Data Source
AI summary
The present application provides a positive electrode material and a lithium-ion battery. The positive electrode material comprises a lithium composite oxide comprising lithium and at least one selected from a group of cobalt (Co), nickel (Ni), manganese (Mn), and a compound on the surface thereof comprising strontium (Sr) and at least one selected from a group of silicon (Si), titanium (Ti). By using above positive electrode material, the increased DC resistance during the circulation of the lithium-ion battery is greatly reduced.