Batteries have shaped much of our modern world. This success is the result of intense collaboration between academia and industry over the past several decades, culminating with the advent of and improvements in rechargeable lithium-ion batteries. As applications become more demanding, there is the risk that stunted growth in the performance of commercial batteries will slow the adoption of important technologies such as electric vehicles. Yet the scientific literature includes many reports describing material designs with allegedly superior performance. A considerable gap needs to be filled if we wish these laboratory-based achievements to reach commercialization. In this Perspective, we discuss some of the most relevant testing parameters that are often overlooked in academic literature but are critical for practical applicability outside the laboratory. We explain metrics such as anode energy density, voltage hysteresis, mass of non-active cell components and anode/cathode mass ratio, and we make recommendations for future reporting. We hope that this Perspective, together with other similar guiding principles that have recently started to emerge, will aid the transition from lab-scale research to next-generation practical batteries.

State-of-the-art lithium (Li)-ion batteries are approaching their specific energy limits yet are challenged by the ever-increasing demand of today's energy storage and power applications, especially for electric vehicles. Li metal is considered an ultimate anode material for future high-energy rechargeable batteries when combined with existing or emerging high-capacity cathode materials. However, much current research focuses on the battery materials level, and there have been very few accounts of cell design principles. Here we discuss crucial conditions needed to achieve a specific energy higher than 350 Wh kg(-1), up to 500 Wh kg(-1), for rechargeable Li metal batteries using high-nickel-content lithium nickel manganese cobalt oxides as cathode materials. We also provide an analysis of key factors such as cathode loading, electrolyte amount and Li foil thickness that impact the cell-level cycle life. Furthermore, we identify several important strategies to reduce electrolyte-Li reaction, protect Li surfaces and stabilize anode architectures for long-cycling high-specific-energy cells.

Due to their high energy density and low material cost, lithium-sulfur batteries represent a promising energy storage system for a multitude of emerging applications, ranging from stationary grid storage to mobile electric vehicles. This review aims to summarize major developments in the field of lithium-sulfur batteries, starting from an overview of their electrochemistry, technical challenges and potential solutions, along with some theoretical calculation results to advance our understanding of the material interactions involved. Next, we examine the most extensively-used design strategy: encapsulation of sulfur cathodes in carbon host materials. Other emerging host materials, such as polymeric and inorganic materials, are discussed as well. This is followed by a survey of novel battery configurations, including the use of lithium sulfide cathodes and lithium polysulfide catholytes, as well as recent burgeoning efforts in the modification of separators and protection of lithium metal anodes. Finally, we conclude with an outlook section to offer some insight on the future directions and prospects of lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries have been regarded as one of the most promising candidates for next-generation energy storage owing to their high energy density and low cost. However, the practical deployment of Li-S batteries has been largely impeded by the low conductivity of sulfur, the shuttle effect of polysulfides, and the low areal sulfur loading. Herein, we report the synthesis of uniform Co-Fe mixed metal phosphide (Co-Fe-P) nanocubes with highly interconnected-pore architecture to overcome the main bottlenecks of Li-S batteries. With the highly interconnected-pore architecture, inherently metallic conductivity, and polar characteristic, the Co-Fe-P nanocubes not only offer sufficient electrical contact to the insulating sulfur for high sulfur utilization and fast redox reaction kinetics but also provide abundant adsorption sites for trapping and catalyzing the conversion of lithium polysulfides to suppress the shuttle effect, which is verified by both the comprehensive experiments and density functional theory calculations. As a result, the sulfur-loaded Co-Fe-P (S@Co-Fe-P) nanocubes delivered a high discharge capacity of 1243 mAh g at 0.1 C and excellent cycling stability for 500 cycles with an average capacity decay rate of only 0.043% per cycle at 1 C. Furthermore, the S@Co-Fe-P electrode showed a high areal capacity of 4.6 mAh cm with superior stability when the sulfur loading was increased to 5.5 mg cm. More impressively, the prototype soft-package Li-S batteries based on S@Co-Fe-P cathodes also exhibited superior cycling stability with great flexibility, demonstrating their great potential for practical applications.

Owing to their low cost, high energy densities, and superior performance compared with that of Li-ion batteries, Li-S batteries have been recognized as very promising next-generation batteries. However, the commercialization of Li-S batteries has been hindered by the insulation of sulfur, significant volume expansion, shuttling of dissolved lithium polysulfides (LiPSs), and more importantly, sluggish conversion of polysulfide intermediates. To overcome these problems, a state-of-the-art strategy is to use sulfur host materials that feature chemical adsorption and electrocatalytic capabilities for LiPS species. In this review, we comprehensively illustrate the latest progress on the rational design and controllable fabrication of materials with chemical adsorbing and binding capabilities for LiPSs and electrocatalytic activities that allow them to accelerate the conversion of LiPSs for Li-S batteries. Moreover, the current essential challenges encountered when designing these materials are summarized, and possible solutions are proposed. We hope that this review could provide some strategies and theoretical guidance for developing novel chemical anchoring and electrocatalytic materials for high-performance Li-S batteries.

Stabilizing the polysulfide shuttle while ensuring high sulfur loading holds the key to realizing high theoretical energy of lithium-sulfur (Li-S) batteries. Herein, we present an electrocatalysis approach to demonstrate preferential adsorption of a soluble polysulfide species, formed during discharge process, toward the catalyst anchored sites of graphene and their efficient transformation to long-chain polysulfides in the subsequent redox process. Uniform dispersion of catalyst nanoparticles on graphene layers has shown a 40% enhancement in the specific capacity over pristine graphene and stability over 100 cycles with a Coulombic efficiency of 99.3% at a current rate of 0.2 C. Interaction between electrocatalyst and polysulfides has been evaluated by conducting X-ray photoelectron spectroscopy and electron microscopy studies at various electrochemical conditions.

Because of their high theoretical energy density and low cost, lithium-sulfur (Li-S) batteries are promising next-generation energy storage devices. The electrochemical performance of Li-S batteries largely depends on the efficient reversible conversion of Li polysulfides to LiS in discharge and to elemental S during charging. Here, we report on our discovery that monodisperse cobalt atoms embedded in nitrogen-doped graphene (Co-N/G) can trigger the surface-mediated reaction of Li polysulfides. Using a combination of operando X-ray absorption spectroscopy and first-principles calculation, we reveal that the Co-N-C coordination center serves as a bifunctional electrocatalyst to facilitate both the formation and the decomposition of LiS in discharge and charge processes, respectively. The S@Co-N/G composite, with a high S mass ratio of 90 wt %, can deliver a gravimetric capacity of 1210 mAh g, and it exhibits an areal capacity of 5.1 mAh cm with capacity fading rate of 0.029% per cycle over 100 cycles at 0.2 C at S loading of 6.0 mg cm on the electrode disk.

Lithium-sulfur (Li-S) batteries hold great promise for the applications of high energy density storage. However, the performances of Li-S batteries are restricted by the low electrical conductivity of sulfur and shuttle effect of intermediate polysulfides. Moreover, the areal loading weights of sulfur in previous studies are usually low (around 1-3 mg cm) and thus cannot fulfill the requirement for practical deployment. Herein, we report that porous-shell vanadium nitride nanobubbles (VN-NBs) can serve as an efficient sulfur host in Li-S batteries, exhibiting remarkable electrochemical performances even with ultrahigh areal sulfur loading weights (5.4-6.8 mg cm). The large inner space of VN-NBs can afford a high sulfur content and accommodate the volume expansion, and the high electrical conductivity of VN-NBs ensures the effective utilization and fast redox kinetics of polysulfides. Moreover, VN-NBs present strong chemical affinity/adsorption with polysulfides and thus can efficiently suppress the shuttle effect via both capillary confinement and chemical binding, and promote the fast conversion of polysulfides. Benefiting from the above merits, the Li-S batteries based on sulfur-filled VN-NBs cathodes with 5.4 mg cm sulfur exhibit impressively high areal/specific capacity (5.81 mAh cm), superior rate capability (632 mAh g at 5.0 C), and long cycling stability.

Lithium-sulfur batteries are deemed to be the next generation of cost-effective and high energy density systems for energy storage. However, low conductivity of active materials, shuttle effect and sluggish kinetics of redox reaction lead to serious capacity fading and poor rate performance. Herein, a sodium citrate derived three-dimensional hollow carbon framework embedded with cobalt nanoparticles is designed as the host for sulfur cathode. The introduced cobalt nanoparticles can effectively adsorb the polysulfides, enhance the kinetics of conversion reaction and further improve the cyclic and rate performance. The obtained cathode delivered a high initial discharge capacity of 1280 mAh·g-1 at 0.5C, excellent high-rate performance up to 10C and stable cyclic capacity of 770 mAh·g-1 at 1C for 200 cycles with high Columbic efficiency.

采用自组装及热处理方法合成α-MoC_1-_x纳米晶富集的纳米碳球(α-MoC_1-_x/CNS), 并将其涂覆在商用聚丙烯隔膜上, 对隔膜实现了界面修饰。电化学性能显示, 与普通的聚丙烯隔膜相比, 采用修饰的α-MoC_1-_x/CNS-PP隔膜组装的锂硫电池的循环稳定性和倍率性能均得到明显提升, 在0.5C条件下, 电池首周放电比容量提升至1129.7 mAh/g, 经过100周充放电循环后, 电池仍具有855.5 mAh/g的放电比容量, 且在此循环过程中, 库伦效率始终大于98%。在自放电测试中, 电池经过48 h静置后的容量损失率仅为7.7%。结合α-MoC_1-_x/CNS的微观形貌及XPS分析可知, 在锂硫电池充放电过程中, α-MoC_1-_x/CNS修饰层有效地阻挡了多硫化锂向负极侧的扩散迁移, 且当α-MoC_1-_x与多硫离子接触时能产生Mo-S键、硫代和连多硫酸根产物, 进一步巩固了活性物质被约束的程度, 从而使电池性能得到提升。

For solving the drawbacks of low conductivity and the shuttle effect in a sulfur cathode, various nonpolar carbon and polar metal compounds with strong chemical absorption ability are applied as sulfur host materials for lithium-sulfur (Li-S) batteries. Nevertheless, previous research simply attributed the performance improvement of sulfur cathodes to the chemical adsorption ability of polar metal compounds toward lithium polysulfides (LPS), while a deep understanding of the enhanced electrochemical performance in these various sulfur hosts, especially at the molecular levels, is still unclear. Herein, for a mechanistic understanding of superior metal phosphide host in Li-S battery chemistry, an integrated phosphide-based host of CF/FeP@C (carbon cloth with grown FeP@C nanotube arrays) is chosen as the model, and this binder-free cathode can exclude interference from the binder and conductive additives. With a systematic electrochemical investigation of the loading sulfur in such oxide- and phosphide-based hosts (CF/FeO@C and CF/FeP@C), it is found that CF/FeP@C@S shows much superior Li-S performances. The greatly enhanced performance of CF/FeP@C@S suggests that FeP can well suppress the shuttle effect of LPS and accelerate their transformation during the charge-discharge process. The first-principles calculations reveal the performance variations of FeO and FeP in Li-S batteries mainly because the shifts of the p band of the FeP could accelerate the interfacial electronics transfer dynamics by increasing the electronic concentration in the Fermi level of adsorbed LiS. The current work sheds light on the promising design of superior Li-S batteries from both theoretical and experimental aspects.

Chemistry at the cathode/electrolyte interface plays an important role for lithium-sulfur batteries in which stable cycling of the sulfur cathode requires confinement of the lithium polysulfide intermediates and their fast electrochemical conversion on the electrode surface. While many materials have been found to be effective for confining polysulfides, the underlying chemical interactions remain poorly understood. We report a new and general lithium polysulfide-binding mechanism enabled by surface oxidation layers of transition-metal phosphide and chalcogenide materials. We for the first time find that CoP nanoparticles strongly adsorb polysulfides because their natural oxidation (forming Co-O-P-like species) activates the surface Co sites for binding polysulfides via strong Co-S bonding. With a surface oxidation layer capable of confining polysulfides and an inner core suitable for conducting electrons, the CoP nanoparticles are thus a desirable candidate for stabilizing and improving the performance of sulfur cathodes in lithium-sulfur batteries. We demonstrate that sulfur electrodes that hold a high mass loading of 7 mg cm and a high areal capacity of 5.6 mAh cm can be stably cycled for 200 cycles. We further reveal that this new surface oxidation-induced polysulfide-binding scheme applies to a series of transition-metal phosphide and chalcogenide materials and can explain their stabilizing effects for lithium-sulfur batteries.

锂硫电池高的比能量密度(2600 Wh•kg⁻¹), 使其成为一种很有前景的储能系统. 然而, 在氧化还原反应中, 中间产物多硫化物(LiPSs)的穿梭效应, 以及缓慢的电化学反应动力学导致阴极和阳极的严重降解, 使容量迅速衰减. 在此, 制备了一种多功能磷化铁碳布(FeP/CC)中间层, 为锂硫电池提供了更多的活性位点, 不仅可以物理捕获多硫化物(LiPSs)以抑制穿梭效应, 确保稳定的循环, 而且对LiPSs具有催化能力, 有助于提高电化学反应动力学. 带有FeP/CC中间层的锂硫电池可实现1329 mAh•g⁻¹的首圈放电容量, 在100圈循环后, 仍然能保持在1100 mAh•g⁻¹的可逆容量, 并且FeP/CC表现出优异的对LiPS吸附与催化转化能力. 这种多功能FeP/CC中间层为高稳定性以及高容量的锂硫电池提供了一种可行的思路.