Solid State Battery are any battery technology that uses solid electrodes and solid electrolyte. This offers potential improvements in energy density and safety, but has very significant challenges with cycling, manufacturing and durability of the solid sandwich.
A cell that uses any liquid or gel electrolyte is not a solid state battery.
Solid state battery categories are:
- Inorganic Solid Electrolytes (ISEs) (Ceramic/Glass): characterised by high ionic conductivity and high mechanical strength, helping to suppress lithium dendrites.
- Oxide-based: highly stable and safe, including garnet-type (e.g., LLZO), NASICON-type, and perovskite-type.
- Sulfide-based: Offer the highest ionic conductivity, similar to liquid electrolytes, but face challenges with stability and moisture sensitivity.
- Halides/Other: Emerging materials like halides offer good oxidation stability and conductivity.
- Solid Polymer Electrolytes (SPEs): composed of lithium salts dissolved in a polymer host matrix, such as polyethylene oxide (PEO). They are flexible and easy to process but generally have lower ionic conductivity at room temperature.
- Composite Polymer Electrolytes (CPEs): combine inorganic fillers (like ceramic particles) within a polymer matrix to bridge the gap between high conductivity and flexibility.
The sections below on this page cover the electrolyte taxonomy, packaging pressure, and known unknowns of solid-state batteries at a survey level. Five related pages go deeper on specific engineering questions:
- Solid Electrolyte Comparative Matrix — quantitative conductivity, stability window, modulus, and moisture-sensitivity comparison across sulfide, oxide/garnet, halide, and polymer electrolytes.
- Anode Architectures for Solid-State Batteries — graphite/Si composites, thin lithium foil, anode-free zero-excess designs, and silicon-dominant micro-Si anodes.
- Cathode-Electrolyte Interface & Catholyte Engineering — catholyte percolation, protective coatings, and chemo-mechanical breathing at the cathode.
- Semi-Solid State Battery — the commercial bridge — WeLion, Desay, SES AI, and Factorial Energy’s hybrid and quasi-solid approaches.
- Thermal Runaway & Safety Realities in Solid-State Cells — why removing the liquid electrolyte doesn’t make a cell immune to thermal runaway.
10 things about SSBs that you are often not told
These 10 topics give a reasonable overview of solid-state batteries in terms of what is less transparent in the publicity and hype of solid state. To be clear, we need solid state batteries, but we need to put claims in context and be wary of missing information.
Billy Wu gives a great introduction to Solid State Batteries in this YouTube video.
Things about Solid State Packaging that you are often not told
Packaging is critical because it links to many of the other 9 points in the things you need to know about SSBs. The pressure system remains the biggest unknown. It is rarely talked about, and it has not been proven at scale. High pressures are required by most SSBs to overcome interfacial resistance. This problem is exasperated by the need to accommodate volume changes and further complicated for semi-solid / hybrid cells because liquid can disperse unevenly under pressure.
Solid State Cell Companies
A review of the Solid State Cell Companies and their technology by Dr. Simon Madgwick, Chief Executive Officer, Nuvvon Inc.
Solid-State Manufacturing & Cost Economics
Why the gigafactory, not just the chemistry, is the real bottleneck: dry-room handling and isostatic pressing equipment that a conventional Li-ion line doesn’t need, and the gap between bare-interface lab figures and what production pilot lines actually report for yield.
Solid-State Production Timelines: OEM Claims vs. Actual Dates
Toyota, Samsung SDI, QuantumScape and the Chinese pilot lines, with each OEM’s stated targets set against what has actually reached a production line or a customer so far.
Stack Pressure & Interfacial Resistance for Pack Designers
A cell datasheet’s single “stack pressure” line becomes a structural design problem at pack level: reaction structure mass, compliant fixtures to hold pressure through life, and the failure modes at each end of the pressure range.
Lithium Intensity of Solid-State Batteries
The table below presents the corresponding cell energy densities and the resulting lithium intensity for each cell chemistry. The sulphide electrolyte SSB has the highest lithium intensity, 78% more than the conventional baseline liquid electrolyte cell. This is driven by the solid electrolyte, which has much higher concentrations of lithium than liquid electrolytes. While SSBs will (in the short term) be more expensive to produce than conventional lithium-ion cells, it will be interesting to see how the price of SSBs will vary based on the price of lithium, given their increased lithium intensity.
Research
SOLBAT
An all-solid-state battery would revolutionise the electric vehicles of the future. The successful implementation of an alkali metal negative electrode and the replacement of the flammable organic liquid electrolytes, currently used in Li-ion batteries, with a solid would increase the range of the battery and address the safety concerns. Current efforts to commercialise such batteries worldwide are failing and will continue to fail until we understand the fundamental processes taking place in these devices.
In order to do cutting edge research you need the latest tools and techniques.
Three-Electrode All-Solid-State Battery Cycling
EIS spectra (WE vs RE) of the NMC cathode (red), the graphite anode (blue), the full cell (amber), and the sum of the individual electrode spectra (green) (20 °C, 0% SOC, 2 MHz – 100 mHz, NEISYS).
Grain Boundary Dendrite Growth in Solid-State Electrolytes
Lithium dendrites growing through a solid electrolyte do not behave like the diffuse, roughly uniform plating seen at a liquid electrolyte interface.
In a polycrystalline ceramic or a cold-pressed sulfide pellet, the microstructure itself dictates where lithium goes: dendrites overwhelmingly nucleate and propagate along grain boundaries rather than through the bulk of individual grains, even in materials whose bulk mechanical properties should, on paper, resist them. That gap between theoretical and real-world dendrite resistance is the central puzzle in solid-state electrolyte design, and it plays out differently in oxide/garnet and sulfide chemistries.
See also: No pressure! Nuvvon 5Ah SiC NMC solid state, An Introduction to Solid Polymer Electrolytes, BMW Solid State Research