Lithium Battery Cell Segmentation for Capacity and Lifespan Balance
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Solution Overview
Problem
Lithium secondary batteries with high-capacity cathode active materials face safety concerns due to high voltage activation, leading to gas generation, structural changes, and poor lifespan, making them difficult to commercialize.
Innovation Solution
A method involving two cells with different cathode active materials, one activated above and the other below the uniform potential voltage region, are electrically connected in parallel or series, with gas removal and aging processes applied under varying conditions to balance capacity and lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a lithium-containing compound is activated at high voltage above the uniform potential voltage region (4.3-4.8V) to achieve high capacity, then the battery capacity is improved, but gases are generated and structural changes occur leading to poor lifespan and safety problems
Solution Approach 1:
The battery system is divided into two separate cells: a first cell containing the lithium-containing compound of formula (I) activated at high voltage for high capacity, and a second cell containing a general layered lithium-metal oxide activated at low voltage for stability. These cells are electrically connected in parallel or series to form a composite battery that achieves both high capacity and long lifespan by separating the conflicting activation requirements.
2Quantity of substance
If the lithium-containing compound undergoes structural variation at high voltage to exhibit high capacity, then the capacity is improved, but Li plating occurs locally and ion transfer deteriorates
Solution Approach 1:
The second cell acts as an intermediary component that buffers the harmful effects of high-voltage activation. By electrically connecting the first cell (high voltage, high capacity) with the second cell (low voltage, stable) in parallel or series, the system distributes the electrochemical stress, preventing direct Li plating and ion transfer deterioration in the high-capacity material while still achieving high overall capacity.
3Reliability
If a cathode active material represented by formula (I) is mixed with general layered lithium-metal oxide to compensate for poor lifespan, then lifespan is improved, but the general layered lithium-metal oxide undergoes durability deterioration during high voltage activation
Solution Approach 1:
Instead of mixing cathode materials in a single cell, the invention segments the battery into two separate cells, each optimized for its specific activation voltage range. The first cell uses the lithium-containing compound of formula (I) activated at high voltage (4.3-4.8V or higher) to achieve high capacity, while the second cell uses a general layered lithium-metal oxide activated at low voltage (below 4.3V) to maintain stability and prevent durability deterioration, with both cells electrically connected to work together.
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 approach enhances the capacity and lifespan of lithium secondary batteries by preventing structural changes in the second cell, thereby improving overall battery performance and safety.
Implementation Method 1
the lithium-containing compound used as a cathode active material is subject to structural variation at a high voltage
Implementation Method 2
gases generated during the activation process should be removed
Implementation Method 3
electrically connecting cells each other, each of the cells comprising a cathode active material different from each other
Data Source
AI summary
The present disclosure provides a method for preparing a lithium secondary battery by bringing a first cell using a first cathode active material of formula (I)Li(LixMy−y′M′y′)O2−zAz (I)wherein, x, y, y′, and z satisfy 0<x<0.5, 0.6<y<1.1, 0≤y′<0.2, and 0≤z<0.2,M is any one selected from the group consisting of Mn, Ni, Co, Fe, Cr, V, Cu, Zn, and Ti,M′ is any one selected from the group consisting of Al, Mg and B; andA is any one selected from the group consisting of F, S and Nand a second cell using a second cathode active material being generally used into activation under different voltage conditions, and then electrically connecting the first cell and the second cell in the step of assembling unit cells; and a lithium secondary battery prepared from the method. According to the present disclosure, a lithium secondary battery can be prepared by bringing a first cell using a first cathode active material of formula (I) and a second cell using a second cathode active material being generally used into activation under different voltage conditions, and then electrically connecting the first cell and the second cell in the step of assembling unit cells, thereby achieving high capacity from the first cell and life performance improvement from the second cell in balance.