Energy density (energy per volume) is a key consideration for portable, automotive, and stationary battery applications. Selenium (Se) lithium and sodium metal cathodes are created that are monolithic and free-standing, and with record Se loading of 70 wt%. The carbon host is derived from nanocellulose, an abundant and sustainable forestry product. The composite is extremely dense (2.37 g cm−3), enabling theoretical volumetric capacity of 1120 mA h cm−3. Such architecture is fully distinct from previous Se–carbon nano- or micropowders, intrinsically offering up to 2× higher energy density. For Li storage, the cathode delivers reversible capacity of 1028 mA h cm−3 (620 mA h g−1) and 82% retention over 300 cycles. For Na storage, 848 mA h cm−3 (511 mA h g−1) is obtained with 98% retention after 150 cycles. The electrodes yield superb volumetric energy densities, being 1727 W h L−1 for Li–Se and 980 W h L−1 for Na–Se normalized by total composite mass and volume. Despite the low surface area, over 60% capacity is maintained as the current density is increased from 0.1 to 2 C (30 min charge) with Li or Na. Remarkably, the electrochemical kinetics with Li and Na are comparable, including the transition from interfacial to diffusional control.

Selenium Impregnated Monolithic Carbons as Free-Standing Cathodes for High Volumetric Energy Lithium and Sodium Metal Batteries

Traditional transition metal sulfides (TMSs) have shown favorable potentials in energy storage. Nevertheless, its further usage is plagued by the issues of particle breakage and large volume change. In this work, the nanostructured ternary TMSs coupled with N/S doped carbon protector (NiCoFe-S@NSC) is delicately designed via compositional regulation and spatial structure protection strategies. As lithium ion batteries anode, this electrode gives an impressive capacity of 995.7 mAh/g after running 1000 cycles at 1 A/g. More importantly, NiCoFe-S@NSC electrode still shows a discharge capacity of 221.94 mAh/g after running 20,000 cycles at 10 A/g, reflecting an extremely-low capacity decay rate of 0.0377 ‰ per cycle. As sodium ion batteries anode, a high initial discharge capacity of 896.4 mA h g-1 can be found. Even after running 400 cycles at 5 A/g, the electrode still displays a reversible capacity of 334.5 mAh/g with outstanding coulombic efficiency above 98.0 %. Impressively, LiNixCoyMn1-x-yO2//NiCoFe-S@NSC full cell gives incipient discharge/charge capacities of 186.89/240.18 mAh/g. Moreover, the discharge capacities for the following 100 cycles remain above 150 mAh/g. Thermal runaway tests also demonstrate the higher thermal safety of cells with NiCoFe-S@NSC electrode, accompanying with the promoted activation energy.

Designing of trimetallic-phase ternary metal sulfides coupled with N/S doped carbon protector for superior and safe Li/Na storage.

Na+ batteries (SIBs) have been emerging as the most promising candidate for the next generation of secondary batteries. However, the development of high-performance and cost-effective anode materials is urgently needed for the large-scale applications of SIBs. In this study, carbon dots confined bimetallic sulfide (NiCo2S4) architecture (NiCo2S4@CDs) was proposed and synthesized from assembling nanosheets into cross-stacked superstructure and the subsequent confinement of carbon dots. This novel decussated structure assembly from nanosheets is greatly beneficial to the structure stability of electrode material during the successive charge/discharge processes. Besides, the CDs based carbon conductive network can enhance the electrical conductivity for facilitating the easy transport of electron/Na+. Benefitting from these advantages, NiCo2S4@CDs exhibits high-rate performance and an ultralong cycling life in SIBs. Specifically, the specific capacity of NiCo2S4@CDs can reach the discharge specific capacity as high as 568.9 mAh/g at 0.5 A/g, which can also maintain 302.7 mAh/g after 750 cycles at t 5.0 A/g. Additionally, ex-situ characterization techniques such as ex-situ XRD and ex-situ XPS were employed to further explore the sodium storage mechanism of the NiCo2S4@CDs anode. 

Carbon dots confined nanosheets assembled NiCo2S4@CDs cross-stacked architecture for enhanced sodium ion storage

Sodium-ion batteries are promising candidates for large-scale grid storage systems and other applications. Their foremost advantage derives from superior environmental credentials, enhanced safety as well as lower raw material costs than lithium-ion batteries. It is still challenging to explore desirable anode material. In this study, FeSe2@CoSe2/FeSe2, with a yolk-shell structure was prepared by ion exchange and selenisation. The FeSe2@CoSe2/FeSe2 prepared as anode material for sodium-ion batteries exhibits excellent rate capability due to the synergistic effect of bimetallic selenides and the interfacial effect of the heterostructure. Moreover, it delivers high performance (510 mAh g−1 at 0.2 A g−1), superior rate capability (90% retention at 5 A g−1), and good long-time cycling stability (78% capacity retention after 1800 cycles at a high current density of 2 A g−1). The optimized sodium-ion full cell with FeSe2@CoSe2/FeSe2 as the anode and Na3V2(PO4)3 as the cathode still demonstrates excellent performance. Namely, a capacity of 272 mAh g−1 (at 1 A g−1) within the operating voltage from 1 to 3.8 V can be obtained. This work illustrates the potential of bimetallic selenides with heterostructures for performance enhancement of sodium-ion batteries. 

Yolk-shell FeSe2@CoSe2/FeSe2 heterojunction as anode materials for sodium-ion batteries with high rate capability and stability

Up to now, lithium/sodium ion batteries (LIBs/SIBs) are deemed as the ideal candidates for traditional fossil energy. However, the absence of suitable Li+/Na+ reservoirs and the hazard of thermal runway have plagued their usages. Using Li4Ti5O12 or TiO2 anode promotes the thermal safety of LIBs/SIBs but reduce their electrochemical property. How to achieve the balanced performances has been an urgency. Here, we have delicately designed a 3D micro-nanostructure of CoS2/doped carbon aerogel (CoS2@NCA), via "killing two birds with one stone" strategy. When used as LIBs anode, CoS2@NCA delivers a high capacity of 639.5 mAh g−1 after operating at 1 A g−1 for 250 cycles, giving a low-capacity attenuation rate of 0.048 % per cycle. Meanwhile, the reduced maximum temperature and maximum heating rate of thermal runaway (TR) are observed for cell. When used as SIBs anode, CoS2@NCA delivers a high capacity of 620.9 mAh g−1 at 100th cycle as working at 1 A g−1. Likewise, the activation energy for TR is promoted. Overall, the utilization of CoS2@NCA enables the superior and safe energy storage. 

Metal sulfides encapsulated in doped carbon aerogel towards superior and safe energy storage: Two birds with one stone

Promoting the Na+-storage of NiCo2S4 hollow nanospheres by surfacing Ni–B nanoflakes

Hierarchical Microspheres Constructed by Te@N-Doped Carbon for Efficient Potassium Storage

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Promoting the Na+-storage of NiCo2S4 hollow nanospheres by surfacing Ni–B nanoflakes

Hierarchical Microspheres Constructed by Te@N-Doped Carbon for Efficient Potassium Storage