鋰離子電池是研究上熱門的領域，由於鋰離子電池具有較高的理論電容量以及良好的循環穩定性，被視為優秀的儲能裝置，特別是使用鈷酸鋰或磷酸鋰鐵作為正極材料的鋰離子電池已被廣泛商業化。然而，這種嵌入嵌出型鋰離子電池所能儲存的鋰離子有限，導致電池能量密度受限。
鋰硫電池由於擁有非常高的理論能量密度，加上成本低廉且對環境無汙染，是先進儲能系統的候選者。然而，它們的應用受到許多阻礙，包括可溶性多硫化物的穿梭效應(shuttling effect)、硫與多硫化鋰間緩慢的反應動力學轉換以及正極硫在充放電過程中的體積變化，導致電池壽命嚴重下降。在眾多已開發材料中，由於單原子金屬催化劑，有效催化反應並減少穿梭效應風險，被視為是傑出的材料。除了催化反應，利用材料如：硫化物、氧化物等具有吸附多硫化鋰的特性，可有效解決穿梭效應的發生。
在本研究中，我們利用二氧化矽作為模板，將聚多巴胺包覆在其表面碳化後形成具腦皺褶表面之中空多孔碳球(Hollow Porous Carbon Sphere, HPCS)，實現高比表面積，並在碳球表面以過渡金屬鐵做為單原子金屬來源將其改質修飾，形成HPCS@SA(Fe)，結構中的單原子Fe可做為單原子催化劑(Single-Atom Catalysts, SACs)，用以催化多硫化鋰的轉換反應提升電池效能，於充放電速率0.1 C下可以提供1134 mAh/g的比電容，在0.2、0.5、1和2 C下分別能提供：698、613、542以及327 mAh/g的電容量。另外，本研究也合成出α-MnO2奈米線來錨固多硫化鋰以減緩穿梭效應，提升活性物質硫利用率，維持循環穩定性。在吸附測試中證明α-MnO2奈米線可以迅速吸附多硫化鋰，減少穿梭效應的發生。長效方面在充放電速率1 C、300 圈下仍保有78.8 %的初始放電容量，每次容量損失率僅有0.071 %。
最後，結合上述優點，將HPCS@SA(Fe)複合α-MnO2奈米線依不同比例混合。當HPCS@SA(Fe)與α-MnO2以1:2混合時，在0.1 C下與純HPCS@SA(Fe)相比，初始比電容量些微下降至1095 mAh/g，但在高倍率下表現較優異，在 1和2 C下分別能提供 504以及343 mAh/g的比電容量。1 C下的長效循環，在300圈後仍保有81.3 %的初始放電容量，每次容量損失率僅有0.062 %，具有優異的穩定性。

Lithium-ion batteries draw extensive and intensive research attention because of their high theoretical capacities and excellent cycle stability, making them a prominent energy storage device. Particularly, lithium-ion batteries, using materials like lithium cobalt oxide or lithium iron phosphate for positive electrodes, have been widely commercialized. However, the intercalation/deintercalation based lithium-ion batteries are limited in their ability to store lithium ions, thus restricting their energy densities.
Lithium-sulfur batteries, on the other hand, possess a very high theoretical energy density, and are cost-effective and environmental friendly, making them promising for advanced energy storage systems. However, their practical applications face several challenges, including the shuttle effect of soluble polysulfides, sluggish reaction kinetics between sulfur and lithium polysulfides, and volume changes in the sulfur cathode during charge-discharge cycles, leading to significant decay in battery life.
Among the various materials developed, single-atom metal catalysts are considered outstanding because of their high catalytic efficiency toward conversion reaction between sulfur and lithium polysulfides to suppress the shuttle effect. Additionally, materials such as sulfides and oxides with adsorption capabilities for lithium polysulfides are effective in mitigating shuttle effects.
In this study, we utilized silica as a template and coated it with polydopamine, followed by carbonization and subsequent etching removal of the silica template to form hollow porous carbon spheres (HPCS) of brain-fold-like surfaces. These HPCS were then implanted with transition metal iron as a source for formation of metal single-atoms, resulting in HPCS@SA(Fe) structures where Fe single-atoms act as single-atom catalysts (SACs). These SACs can catalyze the conversion reaction of lithium polysulfides to enhance battery performances. At a charge-discharge rate of 0.1 C, the battery exhibited an initial specific capacity of 1134 mAh/g, and specific capacities of 698, 613, 542, and 327 mAh/g were achieved at 0.2, 0.5, 1, and 2 C, respectively.
Furthermore, α-MnO2 nanowires were synthesized to adsorb lithium polysulfides, thereby reducing shuttle effects and enhancing the utilization of sulfur active material for improved cycling stability. Adsorption tests demonstrated that α-MnO2 nanowires efficiently adsorb lithium polysulfides, mitigating shuttle effects. Long-term cycling at 1 C rate for 300 cycles retained 78.8% of the initial discharge capacity, with a small capacity loss rate of 0.071% per cycle.
Finally, combining the advantages mentioned above, HPCS@SA(Fe) was composited with α-MnO2 nanowires in different ratios. When mixed at a ratio of 1:2, the composite exhibited a slightly reduced initial specific capacity of 1095 mAh/g at 0.1 C compared to pure HPCS@SA(Fe), yet demonstrated superior performances at higher rates, providing specific capacities of 504 and 343 mAh/g at 1 and 2 C, respectively. Long-term cycling at 1 C rate for 300 cycles maintained 81.3% of the initial discharge capacity, with a small capacity loss rate of 0.062% per cycle, showcasing excellent stability.

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