Poor cycling stability and safety concerns regarding lithium (Li) metal anodes are two major issues preventing the commercialization of high-energy density Li metal-based batteries. Herein, a novel tri-layer separator design that significantly enhances the cycling stability and safety of Li metal-based batteries is presented. A thin, thermally stable, flexible, and hydrophilic cellulose nanofiber layer, produced using a straightforward paper-making process, is directly laminated on each side of a plasma-treated polyethylene (PE) separator. The 2.5 µm thick, mesoporous (≈20 nm average pore size) cellulose nanofiber layer stabilizes the Li metal anodes by generating a uniform Li flux toward the electrode through its homogenous nanochannels, leading to improved cycling stability. As the tri-layer separator maintains its dimensional stability even at 200 °C when the internal PE layer is melted and blocks the ion transport through the separator, the separator also provides an effective thermal shutdown function. The present nanocellulose-based tri-layer separator design thus significantly facilitates the realization of high-energy density Li metal-based batteries.

While the use of silicon‐based electrodes can increase the capacity of Li‐ion batteries considerably, their application is associated with significant capacity losses. In this work, the influences of solid electrolyte interphase (SEI) formation, volume expansion, and lithium trapping are evaluated for two different electrochemical cycling schemes using lithium‐metal half‐cells containing silicon nanoparticle–based composite electrodes. Lithium trapping, caused by incomplete delithiation, is demonstrated to be the main reason for the capacity loss while SEI formation and dissolution affect the accumulated capacity loss due to a decreased coulombic efficiency. The capacity losses can be explained by the increasing lithium concentration in the electrode causing a decreasing lithiation potential and the lithiation cut‐off limit being reached faster. A lithium‐to‐silicon atomic ratio of 3.28 is found for a silicon electrode after 650 cycles using 1200 mAhg−1 capacity limited cycling. The results further show that the lithiation step is the capacity‐limiting step and that the capacity losses can be minimized by increasing the efficiency of the delithiation step via the inclusion of constant voltage delithiation steps. Lithium trapping due to incomplete delithiation consequently constitutes a very important capacity loss phenomenon for silicon composite electrodes.

All-solid-state batteries are intensively investigated, although their performance is not yet satisfactory for large-scale applications. In this context, the combination of Li10GeP2S12 solid electrolyte and LiNi1-x-yCoxMnyO2 positive electrode active materials is considered promising despite the yet unsatisfactory battery performance induced by the thermodynamically unstable electrode|electrolyte interface. Here, we report electrochemical and spectrometric studies to monitor the interface evolution during cycling and understand the reactivity and degradation kinetics. We found that the Wagner-type model for diffusion-controlled reactions describes the degradation kinetics very well, suggesting that electronic transport limits the growth of the degradation layer formed at the electrode|electrolyte interface. Furthermore, we demonstrate that the rate of interfacial degradation increases with the state of charge and the presence of two oxidation mechanisms at medium (3.7 V vs. Li+/Li < E < 4.2 V vs. Li+/Li) and high (E ≥ 4.2 V vs. Li+/Li) potentials. A high state of charge (>80%) triggers the structural instability and oxygen release at the positive electrode and leads to more severe degradation.

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All‐solid‐state batteries with conversion‐type cathodes promise to exceed the performance of lithium‐ion batteries due to their high theoretical specific energy and potential safety. However, the reported performance of solid‐state batteries is still unsatisfactory due to poor electronic and ionic conduction in the composite cathodes. Here, in situ formation of active material as well as highly effective ion‐ and electron‐conducting paths via electrochemical decomposition of Li6PS5Cl0.5Br0.5 (LPSCB)/multiwalled carbon nanotube mixtures during cycling is reported. Effectively, the LPSCB electrolyte forms a multiphase conversion‐type cathode by partial decomposition during the first discharge. Comprehensive characterization, especially operando pressure monitoring, reveals a co‐redox process of two redox‐active elements during cycling. The monolithic LPSCB‐based cell shows stable cycling over 1000 cycles with a very high capacity retention of 94% at high current density (0.885 mA cm−2, ≈0.7 C) at room temperature and a high areal capacity of 12.56 mAh cm−2 is achieved.

Ni-rich Li­(Ni1–x–y Co x Mn y )­O2-based cathodes still suffer from low cycling stability, which arises from capacity fading and impedance rise due to parasitic side reactions at the interface. Surface coatings have shown promising results in stabilizing the cathode surface and improving the cycling stability. However, a comprehensive understanding on the beneficial effect of the coating is still missing. In this paper, we used a solution-based technique to coat Ni-rich Li­(Ni0.70Co0.15Mn0.15)­O2 with a thin Al2O3 layer followed by post-annealing at 600 °C. Electrochemical characterization shows a drastic improvement of the cathode’s cycling stability due to the coating. After post-annealing, the cycling stability is even further improved, accompanied with its C-rate performance. Structural characterization confirms that annealing results in the formation of an amorphous Al2O3/LiAlO2 coating layer, which exhibits increased lithium-ion conductivity compared to the Al2O3 coating. More importantly, temperature-dependent impedance measurements reveal that the coatings do not affect the activation energy of the charge transport, which guarantees a sufficient electronic conductivity between the secondary NCM particles in the cathode. Thus, the Al2O3/LiAlO2 layer not only inhibits direct contact between electrode and electrolyte, preventing side reactions and stabilizes the performance, but also facilitates conductive pathways for lithium ions while preserving the electronic connectivity between cathode’s particles, leading to a low interfacial resistance and excellent rate capability. The results show the importance of providing a sufficiently high electrical conductivity accompanied with low activation energies in coating layers for both ions and electrons, which needs to be considered in design strategies for next-generation lithium-ion batteries.

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Pulverization of electrode materials and loss of electrical contact have been identified as the major causes for the performance deterioration of alloy anodes in Li‐ion batteries. This study presents the hierarchical arrangement of spatially confining silicon nanoparticles (Si NPs) within graphene foam (GF) for alleviating these issues. Through a freeze‐drying method, the highly oriented GF monolith is engineered to fully encapsulate the Si NPs, serving not only as a robust framework with the well‐accessible thoroughfares for electrolyte percolation but also a physical blocking layer to restrain Si from direct exposure to the electrolyte. In return, the pillar effect of Si NPs prevents the graphene sheets from restacking while preserving the highly efficient electron/Li+ transport channels. When evaluated as a binder‐free anode, impressive cycle performance is realized in both half‐cell and full‐cell configurations. Operando X‐ray diffraction and in‐house X‐ray photoelectron spectroscopy confirm the pivotal protection of GF to sheathe the most volume‐expanded lithiated phase (Li15Si4) at room temperature. Furthermore, a free‐standing composite film is developed through readjusting the pore size in GF/Si monolith and directly integrated with nanocellulose membrane (NCM) separator. Because of the good electrical conductivity and structural integrity of the GF monolith as well as the flexibility of the NCM separator, the as‐developed GF/Si‐NCM electrode showcases the potential use in the flexible electronic devices.