Lithium-Rich Manganese Oxide Cathode Activation to Limit Cation Mixing
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Solution Overview
Problem
Lithium-rich transition metal oxides with a layered structure experience increased positive electrode resistance due to oxygen desorption and cation mixing during high-voltage activation, which affects the performance of lithium secondary batteries.
Innovation Solution
A lithium secondary battery comprising lithium-rich manganese-based oxide with a specific manganese content and lithium-to-metal ratio, activated under controlled charging conditions to minimize oxygen desorption and cation mixing, using a two-step charging process with varying C-rates to form a robust SEI film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high-voltage activation (4.4V or more) is performed to achieve high capacity, then lithium utilization is improved, but oxygen desorption and cation mixing are induced causing increased positive electrode resistance
Solution Approach 1:
The activation process is divided into multiple voltage stages (first activation at 4.4V or higher, second activation at 4.6V or higher) rather than applying high voltage in a single step. This segmented approach allows controlled lithium extraction and SEI film formation at each stage, achieving high lithium utilization while managing resistance increase through progressive activation.
Solution Approach 2:
A preliminary activation step is performed before full high-voltage charging to form an initial SEI film and prepare the electrode structure. This preliminary action prevents excessive resistance increase during subsequent high-voltage charging by pre-stabilizing the electrode interface.
2Use of energy by moving object
If high-voltage activation is performed to increase capacity, then energy density is improved, but oxygen desorption occurs causing performance degradation
Solution Approach 1:
The activation process uses periodic voltage cycling with alternating charge and discharge steps at different voltage levels. This periodic action allows oxygen desorption to occur in controlled intervals rather than continuously, managing the harmful effect while achieving the desired capacity activation.
Solution Approach 2:
The voltage parameters are dynamically adjusted during activation, switching between 4.4V and 4.6V or higher based on the activation stage. This parameter change strategy optimizes lithium extraction efficiency while controlling oxygen desorption by avoiding sustained exposure to maximum voltage.
3Quantity of substance
If high-voltage activation is performed to achieve high capacity, then battery capacity is improved, but cation mixing is induced increasing resistance
Solution Approach 1:
The activation process is segmented into multiple voltage stages with intermediate discharge steps. This segmentation prevents excessive cation mixing by limiting the duration and intensity of high-voltage exposure, achieving capacity activation while controlling resistance increase from cation mixing.
Solution Approach 2:
The activation protocol dynamically adjusts voltage levels and charging rates based on the state of activation. This dynamic approach optimizes the balance between achieving high capacity and minimizing cation mixing-induced resistance by adapting conditions to the current electrode state.
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 battery exhibits reduced positive electrode resistance and improved output characteristics while maintaining high capacity, with a discharge curve area in the 2.0 to 3.5V range minimized to suppress cation mixing and oxygen redox reactions.
Implementation Method 1
a first charging step of charging the battery cell at a C-rate of less than 0.5C, and a second charging step of charging the battery cell at a C-rate of 0.5C or more
Implementation Method 2
when such a high-voltage activation step is performed, oxygen desorption and cation mixing are induced in the crystal structure of the lithium-rich transition metal oxide
Implementation Method 3
when such a high-voltage activation step is performed, oxygen desorption and cation mixing are induced in the crystal structure of the lithium-rich transition metal oxide
Data Source
AI summary
A lithium secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes lithium-rich manganese-based oxide in which a content of manganese in all metals excluding lithium is greater than 50 mol %, and a ratio of a number of moles of lithium to a number of moles of all metals excluding lithium (Li/Me) is greater than 1. When a total discharge curve area is defined as 100% in a dQ/dV graph which is obtained by differentiating a graph of a voltage V and a battery discharge capacity Q measured while charging the lithium secondary battery to 4.6V at 0.1C and then discharging it to 2.0V at 0.1C, the discharge curve area in a voltage range of 2.0 to 3.5V is 35% or less. Also provided is a method for manufacturing the same.