NASICON Solid-State Electrolyte Composition for High-Voltage Battery Stability
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Solution Overview
Problem
All-solid-state batteries with 5-V-level positive-electrode active materials face challenges in cycle stability due to secondary reactions involving the solid-state electrolyte, leading to capacity drop and increased internal resistance, especially when a NASICON-type solid-state electrolyte with added Co is used.
Innovation Solution
The battery design incorporates a solid-state electrolyte with a NASICON-type crystalline structure and a specific composition LixAyCozM′aM″bP3Oc in the vicinity of the electrode layers, suppressing lithium extraction during charging and maintaining high cycle stability by controlling the valence and content ratios of elements, thereby preventing secondary reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a NASICON-type solid-state electrolyte with added Co is used to achieve co-sintering with LiCoPO4, then sintering compatibility is improved, but secondary reactions occur at high voltage leading to capacity drop and cycle deterioration
Solution Approach 1:
The patent applies local quality by creating a concentration gradient of Co in the solid-state electrolyte, with lower Co content near the positive electrode interface compared to the bulk material. This localized compositional adjustment prevents secondary reactions at the electrode-electrolyte interface while maintaining the co-sintering capability in the bulk material, thus resolving the contradiction between manufacturability and cycle stability.
Solution Approach 2:
The patent changes the compositional parameters of the solid-state electrolyte by controlling the Co content within a specific range (0.01 ≤ x < 0.5 in Li1-xLaxCo0.2Mg0.1Mn0.6-xO3-δ) and adjusting the oxygen deficiency parameter (δ). These parameter changes optimize the electrolyte's resistance to secondary reactions at high voltage while preserving its ability to co-sinter with LiCoPO4, thereby improving cycle stability without sacrificing manufacturing ease.
2Quantity of substance
If a positive-electrode active material operating at high potential (near 5 V) is applied to improve energy density, then energy density is improved, but the electrolyte undergoes decomposition reactions leading to capacity drop
Solution Approach 1:
The patent changes the chemical composition parameters of the solid-state electrolyte, specifically controlling the Co content and oxygen deficiency stoichiometry, to adjust the electrochemical stability window of the electrolyte. This enables the electrolyte to withstand the high operating voltage (near 5 V) of LiCoPO4 without undergoing decomposition reactions, thus maintaining both high energy density and good cycle characteristics.
Solution Approach 2:
The patent employs a composite solid-state electrolyte material combining multiple elements (Li, La, Co, Mg, Mn, O) with a perovskite structure. This composite material design provides both the structural stability needed to resist high-voltage decomposition and the ionic conductivity required for high-rate performance, resolving the contradiction between energy density and cycle stability.
3Productivity
If repeated charging and discharging under 5 V is performed to utilize high-capacity active material, then energy capacity is improved, but the electrolyte gradually undergoes decomposition reaction leading to increased internal resistance
Solution Approach 1:
The patent applies local quality by creating a protective interface layer or modifying the electrolyte composition locally near the positive electrode to resist secondary reactions. This localized modification prevents the gradual decomposition that would otherwise occur during repeated 5 V charging/discharging, thereby maintaining low internal resistance while utilizing the high energy capacity of the active material.
Solution Approach 2:
The patent applies preliminary action by pre-modifying the solid-state electrolyte composition before battery assembly, incorporating elements and stoichiometric ratios that preemptively protect against decomposition during cycling. This preliminary compositional adjustment ensures the electrolyte is resistant to secondary reactions from the outset, preventing internal resistance increase during subsequent high-capacity operation.
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 results in an all-solid-state battery with improved long-term cycle stability and minimal capacity drop, ensuring high ion conductivity and reduced internal resistance.
Implementation Method 1
a solid-state electrolyte layer (3) containing a solid-state electrolyte (33) having a NASICON-type crystalline structure
Implementation Method 2
the solid-state electrolyte layer (3) in the vicinity of the first electrode layer (1b) is expressed by a composition LixAyCozM′aM″bP3Oc... suppressing lithium extraction during charging and maintaining high cycle stability
Data Source
AI summary
An all-solid-state battery includes a pair of electrode layers consisting of first and second electrode layers, and a solid-state electrolyte layer positioned between the pair of electrode layers, wherein the first electrode layer contains an electrode active material having an olivine-type crystalline structure, the solid-state electrolyte layer contains a solid-state electrolyte having a NASICON-type crystalline structure, and the solid-state electrolyte layer in the vicinity of the first electrode layer is expressed by a composition formula LixAyCozM′aM″bP3Oc. The all-solid-state battery can improve the long-term cycle stability.