Mg attracts much research interest as anode material for Ni-MH batteries thanks to its lightweight, cost-effectiveness and high theoretical capacity (2200 mA h g⁻¹). However, its practical application is tremendously challenged by the poor hydrogen sorption kinetics, passivation from aggressive aqueous electrolytes, and insulating nature of MgH₂. Mg-based alloys exhibit enhanced hydrogen sorption kinetics and electrical conductivity, but significant amount of costly transition metal elements are required. In this work, we have, for the first time, utilized non-alloyed but catalyzed Mg as anode for Ni-MH batteries. 5 mol.% TiF₃ was added to nanosized Mg for accelerating the hydrogen sorption kinetics. Several strategies for preventing the problematic passivation of Mg have been studied, including protective encapsulation of the electrode and utilizing room-temperature/high-temperature ionic liquids and an alkaline polymer membrane as working electrolyte. Promising electrochemical performance has been achieved in this Mg–TiF₃ composite anode based Ni-MH batteries with room for further improvements.

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All-solid-state Li-ion batteries promise safer electrochemical energy storage with larger volumetric and gravimetric energy densities. A major concern is the limited electrochemical stability of solid electrolytes and related detrimental electrochemical reactions, especially because of our restricted understanding. Here we demonstrate for the argyrodite-, garnet- and NASICON-type solid electrolytes that the favourable decomposition pathway is indirect rather than direct, via (de)lithiated states of the solid electrolyte, into the thermodynamically stable decomposition products. The consequence is that the electrochemical stability window of the solid electrolyte is notably larger than predicted for direct decomposition, rationalizing the observed stability window. The observed argyrodite metastable (de)lithiated solid electrolyte phases contribute to the (ir)reversible cycling capacity of all-solid-state batteries, in addition to the contribution of the decomposition products, comprehensively explaining solid electrolyte redox activity. The fundamental nature of the proposed mechanism suggests this is a key aspect for solid electrolytes in general, guiding interface and material design for all-solid-state batteries.

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In our efforts to address the issues of Si based anodes for Li ion batteries, such as limited active mass loading, rapid capacity degradation and low scalability in manufacturing, we reported a scalable, high mass loading, and additive-free Si nanoparticles (NP) deposition based electrode, but the achieved capacity and cycle life were still limited. In order to improve the reversible capacity and cycling stability of this Si NP deposition electrode, in this work, we have investigated various substrates for Si deposition, including carbon paper (CP), preheated CP and stainless steel felt/mesh (SSF/SSM), and their influences on the electrochemical Li-ion storage performance of the Si NP electrodes. Meanwhile, protective encapsulations of amorphous carbon or silicon nitride on Si NP has been performed and the capabilities of these coatings in improving the cycling stability of Si NP electrodes have been researched. It is found that a carbon-coated Si NP deposition on an SSM substrate achieves an extraordinary cycling stability in electrochemical Li-ion storage for 500 cycles with an average capacity loss of 0.09% per cycle, showing significantly improved commercial viability of Si NP deposition based electrodes in high-energy-density Li-ion batteries.

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Rechargeable aqueous zinc-ion batteries (ZIBs) are promising for cheap stationary energy storage. Challenges for Zn-ion insertion hosts are the large structural changes of the host structure upon Zn-ion insertion and the divalent Zn-ion transport, challenging cycle life and power density respectively. Here a new mechanism is demonstrated for the VO ₂ cathode toward proton insertion accompanied by Zn-ion storage through the reversible deposition of Zn ₄ (OH) ₆ SO ₄ ·5H ₂ O on the cathode surface, supported by operando X-ray diffraction, X-ray photoelectron spectroscopy, neutron activation analysis, and density functional theory simulations. This leads to an initial discharge capacity of 272 mAh g ⁻¹ at a current density of 3.0 A g ⁻¹ , of which 75.5% is maintained after 945 cycles. It is proposed that the competition between proton and Zn-ion insertion in the VO ₂ host is determined by the solvation energy of the salt anion and proton insertion energetics, where proton insertion has the advantage of minimal structural distortion leading to a long cycle life. As the discharge kinetics are capacitive for the first half of the process and diffusion limited for the second half, the VO ₂ cathode takes the middle road possessing both fast kinetics and high practical capacities revealing a reaction mechanism that provides new perspective for the development of aqueous ZIBs.

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Modern life is moving towards a mobile and sustainable energy economy, in which rechargeable batteries play an essential role as a power supply. The current battery of choice is Li ion battery that is dominating the market but faces great challenges for future use mainly due to the demand for higher capacities and target for cost reduction. Next-generation rechargeable batteries such as Li-O2, Li-S and Na ion batteries, which offers higher capacities and cost-effectiveness, are being intensively researched as potential solutions to meet the future energy storage demand.  This thesis focuses on the search of high-performance anode materials for both Li and Na ion batteries, including metallic Li and Na, Si, MgH2, and black P and Sn4P3 based composites. Various methods are involved to synthesize the active materials and electrodes in a cost-effective manner; and comprehensive characterization on the physico-chemical and electrochemical properties has been performed to provide fundamental understanding and insights into the electrochemical processes. This work has achieved long-lifespan and safe Li and Na metal anodes by suppressing the hazardous dendrite growth. The Si, P and MgH2 anodes presented in this work also exhibit high and stable electrochemical performance for Li and Na ion storage. Notably, the Na ion uptake in Si and MgH2 has been, for the first time, realized in experiments. This research shows great promise towards the commercial introduction of these anodes in next-generation high energy density Li and Na ion batteries.@en

Li and Na metals have the highest theoretical anode capacity for Li/Na batteries, but the operational safety hazards stemming from uncontrolled growth of Li/Na dendrites and unstable electrode-electrolyte interfaces hinder their real-world applications. Recently, the emergence of 3D conductive scaffolds aimed at mitigating the dendritic growth to improve the cycling stability has gained traction. However, while achieving 3D scaffolds that are conducive to completely prevent dendritic Li/Na is challenging, the routes proposed to fabricate 3D scaffolds to date are often complex and expensive. This not only leads to sub-optimal battery performance but can make the manufacturing nearly unachievable, compromising their commercial viability. We herein introduce a facile and single-step route to honeycomb-like 3D porous Ni@Cu scaffolds via a hydrogen bubble dynamic template (HBDT) electrodeposition method. The current collectors fabricated by this method offer highly stable cycling performance of Li plating/stripping (>300 cycles at 0.5 mAh cm⁻² and over 200 cycles at 1.0 mAh cm⁻²), attributed to their ability to effectively accommodate Li/Na deposits in their porous networks and to delocalize the charge distribution. The beneficial role of LiNO₃ as an electrolyte additive in improving the mechanical integrity of solid electrolyte interface (SEI) and mechanistic insights into how the 3D porous structure facilitates Li/Na plating/stripping are comprehensively presented. Finally, with an outstanding cycling performance of reversible Na deposition (over 240, 110 and 50 cycles for 0.5, 1.0 and 2.0 mAh cm⁻² at 1.0 mA cm⁻²), our findings open new doors to expedite the development of Li/Na metal battery technology.

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Electrical mobility demands an increase of battery energy density beyond current lithium-ion technology. A crucial bottleneck is the development of safe and reversible lithium-metal anodes, which is challenged by short circuits caused by lithium-metal dendrites and a short cycle life owing to the reactivity with electrolytes. The evolution of the lithium-metal-film morphology is relatively poorly understood because it is difficult to monitor lithium, in particular during battery operation. Here we employ operando neutron depth profiling as a noninvasive and versatile technique, complementary to microscopic techniques, providing the spatial distribution/density of lithium during plating and stripping. The evolution of the lithium-metal-density-profile is shown to depend on the current density, electrolyte composition and cycling history, and allows monitoring the amount and distribution of inactive lithium over cycling. A small amount of reversible lithium uptake in the copper current collector during plating and stripping is revealed, providing insights towards improved lithium-metal anodes.

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MgH₂ has been considered as a potential anode material for Li ion batteries due to its low cost and high theoretical capacity. However, it suffers from low electronic conductivity and slow kinetics for hydrogen sorption at room temperature that results in poor reversibility, cycling stability and rate capability for Li ion storage. This work presents a MgH₂–TiF₃@CNT based Li ion battery anode manufactured via a conventional slurry based method. Working with a liquid electrolyte at room temperature, it achieves a high capacity retention of 543 mAh g⁻¹ in 70 cycles at 0.2 C and an improved rate capability, thanks to the improved hydrogen sorption kinetics with the presence of catalytic TiF₃. Meanwhile, the first realization of Na ion uptake in MgH₂ has been evidenced in experiments.

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The original HTML version of this Article omitted to list Zhengcao Li as a corresponding author. Correspondingly, the original PDF version of this Article incorrectly stated that ‘Correspondence and requests for materials should be addressed to M.W. (email: [email protected])’, instead of the correct ‘Correspondence and requests for materials should be addressed to Z.L. (email: [email protected]) or to M.W. (email: [email protected])’. This has been corrected in both the PDF and HTML versions of the Article.

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Phosphorus and tin phosphide based materials that are extensively researched as the anode for Na-ion batteries mostly involve complexly synthesized and sophisticated nanocomposites limiting their commercial viability. This work reports a Sn₄P₃-P (Sn:P = 1:3) at graphene nanocomposite synthesized with a novel and facile mechanochemical method, which exhibits unrivalled high-rate capacity retentions of >550 and 371 mA h g^-1 at 1 and 2 A g^-1, respectively, over 1000 cycles and achieves excellent rate capability (>815, ≈585 and ≈315 mA h g^-1 at 0.1, 2, and 10 A g^-1, respectively).

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Nanostructured silicon has been intensively investigated as a high capacity Li-ion battery anode. However, the commercial introduction still requires advances in the scalable synthesis of sophisticated Si nanomaterials and electrodes. Moreover, the electrode degradation due to volume changes upon de-/lithiation, low areal electrode capacity, and application of large amounts of advanced conductive additives are some of the challenging aspects. Here we report a Si electrode, prepared from direct deposition of Si nanoparticles on a current collector without any binder or conducting additives, that addresses all of the above issues. It exhibits an excellent cycling stability and a high capacity retention taking advantages of what appears to be a locally protective, yolk-shell reminiscent, solid electrolyte interphase (SEI) formation. Cycling an electrode with a Si nanoparticle loading of 2.2 mg cm⁻² achieved an unrivalled areal capacity retention, specifically, up to 4.2 mAh cm⁻² and ~ 1.5 mAh cm⁻² at 0.8 mA cm⁻² and 1.6 mA cm⁻², respectively.

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Black phosphorus (BP) has received increasing research attention as an anode material in sodium-ion batteries (SIBs), owing to its high capacity, electronic conductivity, and chemical stability. However, it is still challenging for BP-based SIB anodes to achieve a high electrochemical performance utilizing cost-effective materials and synthetic methods. This work presents a sodium-ion anode based on a BP-carbon nanocomposite synthesized from commercial red phosphorus and low-cost super P carbon black. Intimate interactions between BP and carbon are present, which helps to maintain the electrical conduction during cycling and, therefore, a high cycling stability is achieved. It exhibits a high capacity retention of 1381mAhg^-1 for sodium-ion storage after 100 cycles, maintaining 90.5% of the initial reversible capacity. Such high performance/materials cost ratio may provide direction for future phosphorus-based anodes in high energy density SIBs.

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Super P carbon black (SPCB) has been widely used as a conducting additive in Li/Na ion batteries to improve the electronic conductivity. However, there has not yet been a comprehensive study on its structure and electrochemical properties for Li/Na ion uptake, though it is important to characterize its contribution in any study of active materials that uses this additive in non-negligible amounts. In this article the structure of SPCB has been characterized and a comprehensive study on the electrochemical Li/Na ion uptake capability and reaction mechanisms are reported. SPCB exhibits a considerable lithiation capacity (up to 310 mAh g^–1) from the Li ion intercalation in the graphite structure. Sodiation in SPCB undergoes two stages: Na ion intercalation into the layers between the graphene sheets and the Na plating in the pores between the nano-graphitic domains, and a sodiation capacity up to 145 mAh g^–1 has been achieved. Moreover, the influence of the type and content of binders on the lithiation and sodiation properties has been investigated. The cycling stability is much enhanced with sodium carboxymethyl cellulose (NaCMC) binder in the electrode and fluoroethylene carbonate (FEC) in the electrolyte; and a higher content of binder improves the Coulombic efficiency during dis-/charge.

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The lithium air, or Li–O2, battery system is a promising electrochemical energy storage system because of its very high theoretical specific energy, as required by automotive applications. Fundamental research has resulted in much progress in mitigating detrimental (electro)chemical processes; however, the detailed structural evolution of the crystalline Li2O2 and LiOH discharge products, held at least partially responsible for the limited reversibility and poor rate performance, is hard to measure operando under realistic electrochemical conditions. This study uses Rietveld refinement of operando X-ray diffraction data during a complete discharge–charge cycle to reveal the detailed structural evolution of Li2O2 and LiOH crystallites in 1,2-dimethoxyethane (DME) and DME/LiI electrolytes, respectively. The anisotropic broadened reflections confirm and quantify the platelet crystallite shape of Li2O2 and LiOH and show how the average crystallite shape evolves during discharge and charge. Li2O2 is shown to form via a nucleation and growth mechanism, whereas the decomposition appears to start at the smallest Li2O2 crystallite sizes because of their larger exposed surface. In the presence of LiI, platelet LiOH crystallites are formed by a particle-by-particle nucleation and growth process, and at the end of discharge, H2O depletion is suggested to result in substoichiometric Li(OH)1–x, which appears to be preferentially decomposed during charging. Operando X-ray diffraction proves the cyclic formation and decomposition of the LiOH crystallites in the presence of LiI over multiple cycles, and the structural evolution provides key information for understanding and improving these highly relevant electrochemical systems.@en

Si-based anode materials in Li-ion batteries (LIBs) suffer from severe volume expansion/contraction during repetitive discharge/charge, which results in the pulverization of active materials, continuous growth of solid electrolyte interface (SE!) layers, loss of electrical conduction, and, eventually, battery failure. Herein, we present unprecedented low-content phosphorene (single-layer black phosphorus) encapsulation of silicon particles as an effective method for improving the electrochemical performance of Si-based LIB anodes. The incorporation of low phosphorene amounts (1%, mass fraction) into Si anodes effectively suppresses the detrimental effects of volume expansion and SE! growth, preserving the structural integrity of the electrode during cycling and achieving enhanced Coulombic efficiency, capacity retention, and cycling stability for Li-ion storage. Thus, the developed method can also be applied to other battery materials with high energy density exhibiting substantial volume changes.

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