Wound Electrode Body D/B Ratio Control for Battery Capacity Retention
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Solution Overview
Problem
Lithium ion secondary batteries with high-potential positive electrode active materials and inorganic phosphates face challenges in maintaining capacity retention and preventing internal resistance increases, especially when constrained in battery packs.
Innovation Solution
Optimizing the state of winding of the flat-shaped wound electrode body by adjusting the center thickness to boundary thickness ratio within a specific range (1.01 to 1.07) and including inorganic phosphates in the positive electrode active material layer, while applying constraint pressure, to maintain high capacity retention and suppress internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a high-potential positive electrode active material is used to increase battery performance, then the open circuit voltage and energy density are improved, but capacity deterioration occurs due to transition metal elution from acid generation
Solution Approach 1:
An inorganic phosphate compound is introduced as an intermediary substance between the high-potential positive electrode active material and the nonaqueous electrolytic solution. The phosphate acts as an acid-consuming material that neutralizes acid generated during oxidative decomposition of the electrolyte, thereby preventing transition metal elution while allowing the high-potential material to maintain its voltage benefits
Solution Approach 2:
The positive electrode active material layer is designed as a composite containing both the high-potential positive electrode active material and an inorganic phosphate compound. This composite structure allows the phosphate to protect the active material from acid-induced degradation while maintaining the high voltage characteristics, achieving both improved power and reliability
2Reliability
If inorganic phosphate is included in the positive electrode active material layer to prevent transition metal elution, then capacity deterioration is suppressed, but internal resistance increases and durability performance varies depending on winding state
Solution Approach 1:
The invention specifies precise parameter ranges for the winding state, defining the ratio of the outer diameter of the wound electrode body to the width of the electrode sheets to be within 1.05 to 1.15. By controlling this geometric parameter, the winding tightness is standardized, ensuring consistent durability performance and capacity retention across different battery units regardless of variations in the winding process
Solution Approach 2:
The patent discards the approach of using loose or variable winding states and recovers performance consistency by enforcing a specific winding density range. This standardized winding approach eliminates the variability that previously caused durability performance to depend on winding state, making the battery performance predictable and reliable
3Stability of the object's composition
If constraint pressure is applied to the battery pack to constrain unit batteries, then the arrangement stability is improved, but the winding state of the electrode body may deteriorate leading to increased internal resistance
Solution Approach 1:
The invention applies beforehand cushioning by pre-defining the optimal winding state parameters (outer diameter to width ratio of 1.05 to 1.15) that create an buffer against the effects of constraint pressure. This pre-optimized winding state acts as a cushion that prevents excessive deformation when constraint pressure is applied during battery pack assembly, maintaining both arrangement stability and winding integrity
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 configuration enhances the durability and capacity retention of lithium ion secondary batteries, even when including inorganic phosphates, by controlling the winding state and applying appropriate constraint pressure, resulting in a high-potential battery pack with improved performance and durability.
Implementation Method 1
an inorganic phosphate such as lithium phosphate can be included in the positive electrode active material layer... the inorganic phosphate functions as an acid consuming material, thereby suppressing capacity deterioration
Implementation Method 2
applying a constraint pressure in the arrangement direction to constrain the plurality of unit batteries
Data Source
AI summary
The present teaching provides a highly durable lithium ion secondary battery including a flat shape wound electrode body, with which a high capacity retention ratio and suppression of resistance rise are realized, and also provides a battery pack constructed by using the secondary battery as a unit battery. The lithium ion secondary battery (unit battery) provided in accordance with the present teaching has a flat-shaped wound electrode body 20, and in a state in which a constraint pressure is applied in the direction toward the flat surface of the wound electrode body under the same conditions as the conditions when the battery pack is constructed, the condition of a D/B ratio being 1.01 or more and 1.07 or less is satisfied, where, in the lateral cross section of the wound electrode body, a thickness from an inner curve apex V to an outer curve apex P is taken as a center thickness D of a curved R portion, and a thickness from the inner curve apex V to an outer surface S of the wound electrode body along an R portion/F portion boundary line W is taken as a boundary thickness B of the curved R portion.