Separator Covering Layer for Uniform Lithium Metal Deposition
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Solution Overview
Problem
Lithium metal negative electrode secondary batteries face challenges in cycle endurance due to non-uniform lithium metal deposition, leading to rapid capacity retention degradation.
Innovation Solution
Incorporating a separator with a covering layer having a lithium-ion conductor with a conductivity range of 1.0×10−13 to 2.0×10−9 S/cm, which reduces lithium-ion congestion and promotes uniform lithium metal deposition, thereby enhancing cycle endurance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional separator is used in a lithium metal negative electrode secondary battery, then the structure is simple and manufacturing is easy, but lithium metal deposits non-uniformly during charging, leading to rapid capacity retention degradation and poor cycle endurance
Solution Approach 1:
The separator is divided into multiple functional layers: a base separator layer and a covering layer with lithium-ion conductor particles. This segmentation allows each layer to perform its specific function - the base separator provides physical separation and porosity, while the covering layer controls lithium-ion transport and promotes uniform deposition, thereby resolving the contradiction between maintaining simple structure and improving cycle endurance.
Solution Approach 2:
The separator uses a composite structure combining a polyolefin base material with a covering layer containing lithium-ion conductor particles (such as Li3PO4, Li2SiO3, or Li2SiO2) dispersed in a binder resin. This composite material approach enables the separator to simultaneously provide mechanical integrity, ion transport control, and uniform lithium metal deposition promotion, addressing the contradiction between structural simplicity and reliability.
2Reliability
If the lithium-ion conductor has high ionic conductivity (like typical electrolyte solutions at 10^-2 S/cm or solid electrolytes at 10^-2 to 10^-4 S/cm), then ion transport is efficient, but lithium-ion congestion occurs at the interface with the negative electrode, causing non-uniform deposition and reduced cycle life
Solution Approach 1:
The lithium-ion conductor particles are selected with specific conductivity values in the range of 10^-10 to 10^-14 S/cm, which is significantly lower than conventional electrolytes or solid electrolytes. This parameter change optimizes the balance between ion transport efficiency and uniformity of lithium metal deposition, preventing interface congestion while maintaining sufficient ion supply, thus resolving the contradiction between reliability and deposition precision.
Solution Approach 2:
The covering layer is applied specifically on the negative electrode-facing side of the separator, creating a localized functional zone with controlled lithium-ion conductivity. This local quality modification ensures that the conductivity control effect is applied precisely where needed - at the interface region where lithium metal deposition occurs - without affecting the overall separator performance, thereby achieving both reliable cycle endurance and uniform deposition precision.
3Manufacturing precision
If the lithium-ion conductor conductivity is too low (below 1.0×10^-13 S/cm), then lithium-ion congestion is reduced, but lithium-ion supply becomes insufficient, potentially causing other performance degradation
Solution Approach 1:
The covering layer contains lithium-ion conductor particles dispersed in a binder resin matrix, creating a composite structure where the low-conductivity particles provide uniform deposition control while the binder resin and porosity ensure sufficient overall ion supply. This partial action approach - using only enough conductivity control to achieve uniformity without completely blocking ion transport - resolves the contradiction between deposition precision and productivity.
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 effectively improves cycle endurance and power output performance by ensuring uniform lithium metal deposition and reducing battery resistance, as demonstrated by the evaluation results showing enhanced capacity retention and power output.
Implementation Method 1
The covering layer includes a lithium-ion conductor. The lithium-ion conductor has a lithium-ion conductivity from 1.0×10−13 to 2.0×10−9 S/cm.
Implementation Method 2
an insertion reaction takes place. The insertion reaction refers to a reaction of Li ions moving in and out of crystals of a host material (such as graphite, for example).
Implementation Method 3
During discharging, Li metal dissolves into the electrolyte solution.
Implementation Method 4
during charging, Li metal becomes deposited from the electrolyte solution.
Data Source
AI summary
A lithium metal negative electrode secondary battery comprises a positive electrode, a separator, a negative electrode, and an electrolyte solution. The electrolyte solution includes Li ions. The separator is interposed between the positive electrode and the negative electrode. The separator includes a porous base material and a covering layer. The porous base material has a first main face and a second main face. The first main face faces the positive electrode. The second main face faces the negative electrode. The covering layer covers the second main face. The covering layer includes a Li-ion conductor. The Li-ion conductor has a Li-ion conductivity from 1.0×10−13 to 2.0×10−9 S/cm.