Full
HUANG Shaojuan (2000-), female, Master candidate. E-mail: huangsj@emails.bjut.edu.cn
Outline
With the ever-increasing industrial demand for high energy density lithium-ion batteries, lithium-rich manganese-based layered oxide cathodes have attracted much attention due to their high specific capacity and low cost. However, their practical application is hindered by critical drawbacks including low initial Coulombic efficiency, irreversible oxygen release, and severe voltage fade. In this paper, bulk-engineered lithium-rich manganese-based layered oxides with a full concentration gradient were prepared by a room-temperature ammonia plasma interfacial modification strategy. In contrast to direct ammonia sintering, ammonia plasma modification could construct a stable spinel-amorphous composite nano-bifunctional motif ordered interface on the cathode surface that endowed fast Li+ transport kinetics. This bulk-surface functional motif ordering design concept could provide a novel and effective strategy for improving the overall electrochemical performance of lithium-rich oxide cathodes.
A precursor of cobalt-free full-concentration gradient twin-domain lithium-rich manganese-based layered oxide cathode material was synthesized by a co-precipitation method. After washing for impurity removal and vacuum drying, the precursor was uniformly mixed with 3% (in mole fraction) excess Li2CO3 for lithium supplementation and sintered to prepare the cobalt-free gradient lithium-rich manganese-based layered oxide cathode material (GLLOs). To investigate the modification effects of different treatment methods under ammonia atmosphere, the equal mass of GLLOs was subjected to direct ammonia sintering and ammonia plasma modification, respectively. The crystal structure, micro-morphology, electrochemical performance, ion transport kinetics, and transition metal valence state evolution of the materials before and after modification were determined by systematic characterizations including X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, electrochemical measurements, and kinetic analysis, respectively. Furthermore, the regulatory differences of ammonia treatment in different states on the performance of GLLOs and their intrinsic action mechanisms were revealed.
Two distinct ammonia-based treatments (i.e., direct ammonia sintering and ammonia plasma technology) have different impacts on the GLLOs' surface structure, valence variation, electrochemical performance, and stability. Direct ammonia sintering forms a rock salt-amorphous interface with more significant Mn valence reduction, improving initial efficiency and rate capability, while degrading cycling stability. Ammonia plasma constructs a stable spinel-amorphous interface facilitating Li+transport, with a milder Mn valence change, effectively stabilizing interfacial reactions and structure to remarkably enhance long-cycle performance and mitigate voltage decay.
The formation of rock salt and spinel phase functional units on GLLOs surface stems from ammonia-induced TM valence reduction, triggering Li leaching, oxygen vacancy formation, and TM migration to Li layers that drive layered-to-spinel/rock salt transformation. Direct ammonia sintering requires prolonged heating with limited ammonia decomposition, most nitrogen intermediates adsorb on the material surface, causing excessive TM migration and a rock salt-N-rich amorphous interface. Ammonia plasma enables a rapid ammonia decomposition into nitrogen intermediates for quick modification, forming a spinel-amorphous interface that enhances Li+ transport, inhibits oxygen loss, electrolyte corrosion, and stabilizes cycling via short-time treatment.
In this work, twin-domain lithium-rich manganese-based layered oxide cathodes with bulk full-concentration gradient were interface-modified via direct ammonia sintering and ammonia plasma treatment. The effect of interface modification method on the surface structure, electrochemical performance, TMs valence, kinetics, and stability was investigated. Ammonia nitridation could form a 2-3 nm N-containing amorphous interface, alleviating oxygen vacancies and enhancing oxygen redox reversibility. Ammonia plasma, operating at room temperature for minutes, could decompose into nitrogen active species under high electric field, constructing a spinel-amorphous composite interface favorable for Li+ transport. It could avoid Mn over-reduction and spinel-to-rock salt transformation, maintaining TMs reversibility. A robust bulk-surface synergistic stabilization system was established via integrating the bulk full concentration gradient twin-domain design with the surface composite nano-bifunctional motif ordering construction, remarkably boosting the electrochemical performance of the cathodes (i.e., the capacity retention of 81.5% after 900 cycles at 1 C, accompanied by a low voltage decay of only 0.21 mV/cycle). Controllable ammonia decomposition could facilitate a stable interface formation, offering a novel pathway to boost the comprehensive performance of LLOs.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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