Ge-Enriched Spinel Cathode Material for High-Voltage Capacity Retention
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Solution Overview
Problem
Existing positive electrode active materials for non-aqueous electrolyte secondary batteries, such as those disclosed in Patent Literature 1 and 2, often result in reduced discharge capacity due to the substitution of metal elements or the presence of electrochemically inert coating layers.
Innovation Solution
A positive electrode active material comprising a lithium-transition metal composite oxide with a spinel structure, represented by the formula Li1+αNi0.5-xMn1.5-y-zGeyMx+zO4, where 0≤α<0.2, 0≤x<0.2, 0<y<0.45, 0≤z<0.2, and M represents elements like Mg, Al, Sc, Ti, Cr, V, Fe, and Co. This material has a higher mole fraction of Ge on the surface compared to the center, which inhibits oxygen deficiency and maintains battery capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal elements are substituted to prevent deterioration of battery characteristics at high temperature, then reliability is improved, but discharge capacity is reduced
Solution Approach 1:
The patent applies local quality by creating a concentration gradient of Ge element where the surface portion has a higher Ge content (0.05≤Gesurf≤0.4) compared to the central portion (0≤Gebulk≤0.2). This localized differentiation allows the surface to provide protective effects against deterioration while the interior maintains higher Li and transition metal content to preserve discharge capacity, thus resolving the contradiction between reliability and quantity of substance.
2Reliability
If an electrochemically inert coating layer is added to prevent deterioration of battery characteristics, then reliability is improved, but discharge capacity is reduced
Solution Approach 1:
The patent changes the composition parameters by incorporating Ge element with specific concentration ranges (0.05≤Gesurf≤0.4 in surface, 0≤Gebulk≤0.2 in center) into the spinel structure formula Li1+αNi0.5-xMn1.5-y-zGeyMx+zO4. This parameter change allows Ge to provide protective functionality without forming an electrochemically inert coating layer, thereby maintaining discharge capacity while improving reliability.
3Power
If high voltage operation is achieved, then power is improved, but discharge capacity deteriorates
Solution Approach 1:
The patent uses local quality by differentiating Ge concentration between surface (0.05≤Gesurf≤0.4) and center (0≤Gebulk≤0.2) portions. The surface enrichment of Ge stabilizes the structure at high voltage (4.5V or higher), while the Ge-depleted center maintains high Li content (1+α where 0≤α<0.2) to ensure sufficient discharge capacity, thus resolving the contradiction between power and quantity of substance.
Data Source
AI summary
This positive electrode active material for nonaqueous electrolyte secondary batteries includes a lithium transition metal complex oxide that has a spinel structure and that is represented by general formula Li1+αNi0.5-xMn1.5-y-zGeyMx+zO4 (in the formula, 0≤α<0.2, 0≤x<0.2, 0<y<0.45, and 0≤z<0.2 are satisfied, and M represents at least one element selected from the group consisting of Mg, Al, Sc, Ti, Cr, V, Fe, and Co). In a secondary particle of the lithium transition metal complex oxide, the mole number (Gesurf) of Ge at the surface portion when the total number of moles of metal elements other than Li is defined as 2 is larger than the mole number (Gebulk) of Ge at the center portion when the total number of moles of metal elements other than Li is defined as 2.