Lithium metal and solid-state batteries

Lithium metal and solid-state cells on one page: plating and stripping with a cracking SEI and dead lithium, dendrites as faceted nanowires, an anode-free cell on coated copper, a sulfide composite cathode, voids and grain-boundary lithium at a solid electrolyte, and an ALD Al₂O₃ layer that lets lithium wet a garnet. Every caption and number is quoted from the cited papers.

1. Plating and stripping: Lithium metal anodes offer a theoretical capacity of 3,860 mAh g⁻¹, but dendrite growth and low Coulombic efficiency have kept them from commercial use (Fang 2019). Dendrites, the SEI forming and fracturing again and again, and large volume changes leave “dead lithium” and can short-circuit the cell (Wang 2022). Inactive lithium is both Li⁺ in SEI compounds and electrically isolated metallic Li⁰; titration gas chromatography showed the metallic Li⁰ is the dominant source of inactive lithium and capacity loss (Fang 2019). 2. Dendrites: Cryo-electron microscopy shows dendrites in carbonate electrolytes growing as faceted, single-crystalline nanowires along ⟨111⟩ (preferred), ⟨110⟩ or ⟨211⟩, changing direction at kinks with no observable crystallographic defect (Li 2017). Uncontrolled dendrite growth lowers cycling efficiency and raises severe safety concerns (Cheng 2017). 3. Anode-free cells: Anode-free cells leave out the excess lithium on the anode side; uncontrolled Li nucleation, continuous Li loss and unstable Cu interfaces limit them. A ZnO bottom layer on Cu gave uniform nucleation sites and a lithium trithiocyanurate (Li-TCA) top layer acted as a Li reservoir: the first plating/stripping overpotential fell from 76.1 mV (bare Cu) and 40.9 mV (ZnO) to 12.8 mV, and with ~17 mg cm⁻² LiFePO₄ cathodes the cells kept 56.2% of their capacity after 100 cycles, against 47.8% and 34.6% (Chiang 2026). 4. Composite cathode: With highly conductive solid electrolytes many all-solid-state batteries are limited instead by resistance at interfaces: loose physical contact, grain boundaries and chemical and electrochemical reactions (Banerjee 2020). In a sulfide composite cathode Li⁺ and electrons must percolate together through the active particles, their interfaces and the electrolyte particles; the active material’s volume change and decomposition of the sulfide on active-material and carbon surfaces break contacts and raise resistance, and morphology, coatings, particle size and pressure help (Song 2026). 5. Lithium on a solid electrolyte: Stripping lithium faster than it is replenished leaves voids at the interface that accumulate and lead to dendrites on plating; in Li/Li–P–S–Cl/Li cells the critical stripping current was 0.2 and 1.0 mA cm⁻² at 3 and 7 MPa, against 2.0 mA cm⁻² for plating, and creep rather than diffusion brings lithium to the interface (Kasemchainan 2019). In Ta-doped LLZO lithium tends to nucleate and propagate along grain boundaries; pellets with ~3 μm grains showed less Li along them than pellets with grains up to 20 μm (Guo 2024). 6. A wetting interlayer: Garnet electrolytes conduct Li⁺ at nearly 1 mS cm⁻¹ and are stable from lithium metal to ~6 V, but their solid–solid interfaces with electrodes have high impedance; an ultrathin ALD Al₂O₃ layer let lithium wet the garnet and cut the interfacial impedance from 1,710 to 1 Ω cm² at room temperature (Han 2017). Key challenges of solid-state cells are using metal anodes, stabilizing interfaces and keeping physical contact (Famprikis 2019).

Fang et al., “Quantifying inactive lithium in lithium metal batteries”, Nature 2019 (doi:10.1038/s41586-019-1481-z); Wang et al., “Toward dendrite-free metallic lithium anodes: from structural design to optimal electrochemical diffusion kinetics”, ACS Nano 2022 (doi:10.1021/acsnano.2c08480); Li et al., “Atomic structure of sensitive battery materials and interfaces revealed by cryo-electron microscopy”, Science 2017 (doi:10.1126/science.aam6014); Cheng et al., “Toward safe lithium metal anode in rechargeable batteries: a review”, Chem. Rev. 2017 (doi:10.1021/acs.chemrev.7b00115); Chiang et al., “Synergistic interfacial engineering of ZnO-modified Cu current collectors using lithium trithiocyanurate for stable anode-free lithium metal batteries”, ChemSusChem 2026 (doi:10.1002/cssc.202502753); Banerjee et al., “Interfaces and interphases in all-solid-state batteries with inorganic solid electrolytes”, Chem. Rev. 2020 (doi:10.1021/acs.chemrev.0c00101); Song et al., “Electro-chemo-mechanical coupling in composite cathodes of sulfide-based all-solid-state batteries: pathways, degradation, and design rules”, Adv. Sci. 2026 (doi:10.1002/advs.202524187); Kasemchainan et al., “Critical stripping current leads to dendrite formation on plating in lithium anode solid electrolyte cells”, Nat. Mater. 2019 (doi:10.1038/s41563-019-0438-9); Guo & Chan, “Lithium dendrite propagation in Ta-doped Li7La3Zr2O12 (LLZTO): comparison of reactively sintered pyrochlore-to-garnet LLZTO by solid-state reaction and conventional sintering”, ACS Appl. Mater. Interfaces 2024 (doi:10.1021/acsami.3c11421); Han et al., “Negating interfacial impedance in garnet-based solid-state Li metal batteries”, Nat. Mater. 2017 (doi:10.1038/nmat4821); Famprikis et al., “Fundamentals of inorganic solid-state electrolytes for batteries”, Nat. Mater. 2019 (doi:10.1038/s41563-019-0431-3).

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