Solid-State Isn’t a Cathode Chemistry
Battery terminology can be confusing.
NMC, LFP and NCA describe cathode chemistries. Solid-state describes the electrolyte architecture of a battery. They are not competing definitions.
An NMC cathode, for example, can be used with a conventional liquid electrolyte or as part of a solid-state battery architecture. A useful way to think about a battery is as a combination of technologies:
- CATHODE - NMC • LFP • NCA • other advanced chemistries
- ELECTROLYTE - Liquid • Polymer / Composite
- ANODE - Graphite • Silicon Composite • Lithium-metal • Other
Different combinations produce very different battery characteristics.
A solid-state architecture refers primarily to the physical state and ion-conduction architecture of the electrolyte, rather than requiring every material inside the cell to be a rigid solid object. Solid electrolytes may exist as crystalline, polycrystalline or amorphous phases and can include inorganic oxides, sulfides, ceramics, solid polymers and composite electrolyte systems.
Advanced architectures may also incorporate polymeric, gel-like or compliant interfacial materials to improve electrode–electrolyte contact, ionic conductivity, interfacial impedance, manufacturability and electrochemical stability. These materials can be particularly important at the solid-electrolyte interface, where microscopic contact and interfacial resistance strongly influence cell performance. Their presence does not automatically convert the architecture into a conventional liquid-electrolyte lithium-ion cell. “Solid-state” describes the electrolyte architecture and dominant ion-conduction system — not a requirement that every component inside the battery is physically hard, dry or rigid.
Solid-state batteries aren’t rigid blocks; they’re active engineered electrochemical systems.
Safety
No energy storage technology is completely free from fire or failure risk. Overcharging a cell beyond its rated limits, physical damage, electrical faults, excessive temperatures or other unintended operating conditions can create hazardous situations in any high-energy system.
Solid-state battery architectures can reduce key risks associated with conventional batteries, particularly by reducing free flowing liquids, while providing greater performance and reduced thermal-management demands under appropriate operating conditions. This can create additional safety and thermal headroom for higher-power, higher-energy applications.
Density combines these cells with layered electrical, thermal and mechanical protection systems designed to keep the battery within its intended operating limits. We do not claim our products are fire proof.
Quasi, Semi, All Solid State?
Solid-state battery technology isn't one chemistry or one architecture. Quasi-solid-state, semi-solid-state, hybrid solid-state and all-solid-state batteries represent different approaches within the broader solid-state battery (SSB) family, each with its own advantages, limitations and applications.
At Density, we use XSSB as an umbrella reference for this broader family of advanced solid-state technologies used across our products. The “X” reflects the variable architecture - across a portfolio of more than 100 cell options, we can access different combinations of cathode, anode, electrolyte and interface technologies rather than being tied to a single chemistry or definition of solid-state. XSSB is not a brand or trademark, its simply an abbreviation.
Importantly, we don't use XSSB to mean all-solid-state battery (ASSB). All-solid-state is one end of a much broader technology spectrum. Semi-, quasi- and hybrid solid-state architectures can be equally valuable, particularly where their combination of materials provides the best balance of manufacturability, performance, safety, cycle life and cost. Our engineering team selects the architecture according to the application. Across the XSSB cells selected for our products, a defining characteristic is the absence of free-flowing liquid electrolyte observed in the event of puncture, rather than a claim that every component inside the cell is a rigid solid. Solid-state electrolytes and interfaces can incorporate crystalline, amorphous, polymeric, composite and other engineered materials designed to optimise ionic transport and electrochemical performance.
Density partners with advanced battery cell and chemistry specialists to access these different technologies. This allows us to select architectures according to what matters most for each application: Energy density • Power • C-rate • Internal resistance • Cell voltage • Temperature performance • Safety • Cycle life • Cost. One of the fundamental challenges in advanced battery engineering is balancing these characteristics. Maximum energy density may come with different compromises in cycle life, cost or operating requirements, while another architecture may sacrifice some energy density to deliver exceptional power or longevity.
This is a rapidly evolving field. Researchers and engineers around the world continue to advance cathodes, anodes, electrolytes and interfaces to store more energy with less mass and volume, deliver greater power and improve safety and efficiency.
Density XSSB Type Designation
XSSB is Density's umbrella designation for the solid-state battery technologies we use today and those that continue to evolve.
As solid-state technology advances, new materials and architectures can be incorporated into the XSSB family without redefining the platform. Density then uses XSSB stages to group these technologies by their performance characteristics and intended applications, making it easier to understand the balance between energy density, power, C-rate, internal resistance, operating voltage, cycle life, safety and cost.
