The terms semi-solid-state, solid-state and LiFePO4 are often placed in the same comparison, but they do not all describe the same part of a battery. Understanding the difference helps you assess a home battery without treating one technology label as proof of its safety or performance.
In short: A semi-solid-state battery uses a hybrid electrolyte architecture rather than a conventional liquid-electrolyte design or an all-solid-state electrolyte. The exact design may include polymer, gel, ceramic or limited liquid-containing components. It is not automatically a fully solid-state battery. Semi-solid-state also does not replace labels such as LiFePO4 or NMC, because those normally describe cathode chemistry rather than the electrolyte.
What is a semi-solid-state battery?
A semi-solid-state battery uses an electrolyte structure that sits between a conventional liquid-electrolyte design and an all-solid-state electrolyte architecture. The electrolyte allows lithium ions to move between the positive and negative electrodes while the cell charges and discharges.
Depending on the cell design, the electrolyte may include a polymer gel, ceramic or composite framework, porous host material or a limited liquid-containing phase. The terms semi-solid, quasi-solid and gel electrolyte are not always used in exactly the same way.
One peer-reviewed lithium-metal pouch-cell study describes a quasi-solid electrolyte using a host matrix that confines a small amount of liquid electrolyte. This is one design example rather than a universal definition for every commercial cell or home battery.
“Semi-solid-state” is therefore a broad architecture label. The manufacturer should define what the term means for the specific cell and explain which materials, components and test conditions support its claims.
Why semi-solid-state does not mean fully solid-state
A semi-solid-state cell still uses a hybrid or partially immobilised electrolyte arrangement. An all-solid-state battery is designed around a solid electrolyte pathway rather than a hybrid structure containing a liquid or gel phase.
Liquid, gel and solid electrolyte structures
*Terminology varies between research papers and manufacturers, so the stated product definition should always be checked.
The Faraday Institution distinguishes solid-state research through the use and development of solid electrolytes. Its solid-state battery research also covers interface morphology, voiding, dendrite initiation, cracking and lithium penetration.
This is why “solid-state” should not be read as “zero fault risk”. A solid electrolyte changes the cell architecture, but it does not remove the need to manage interfaces, materials, current distribution, manufacturing quality and operating conditions.
Why there is no universal liquid-percentage definition
There is no single percentage that turns every battery into a semi-solid-state battery. A percentage quoted for one product may refer to a mass fraction, a volume fraction, the electrolyte content of a particular component or another manufacturer-defined basis.
Before comparing a percentage, ask:
- Does any liquid or gel phase remain, and where is it located?
- Does the figure refer to the whole cell or only one component?
- Is the percentage measured by mass, volume or another stated basis?
- Is the definition supported by approved technical documentation?
Semi-solid-state vs LiFePO4: two different battery labels
Semi-solid-state and LiFePO4 are not opposite battery types. Semi-solid-state describes the electrolyte architecture, while LiFePO4 describes the cathode chemistry. A battery cell can therefore be both semi-solid-state and LiFePO4.
Think of these as two separate labels. Semi-solid-state describes how ions move through the electrolyte architecture. LiFePO4 or NMC describes the cathode material. One battery cell can carry both labels.
Electrolyte architecture
The electrolyte label answers a structural question: what type of ion-conducting medium is used between the electrodes? Possible descriptions include liquid, gel or quasi-solid, semi-solid and all-solid.
Cathode chemistry
The cathode label answers a materials question: what active material is used at the positive electrode? LiFePO4 means lithium iron phosphate, while NMC refers to lithium nickel manganese cobalt oxide.
The US Department of Energy’s lithium-ion technology assessment identifies LFP and NMC as classes of cathode material. This cathode classification is separate from whether the electrolyte is liquid, gel, semi-solid or all-solid.
Can a semi-solid-state battery use LiFePO4?
Yes. A semi-solid-state cell can use LiFePO4 because electrolyte architecture and cathode chemistry are separate classifications. Knowing one label does not automatically reveal the other.
A quick way to assess the terminology
- First: identify the electrolyte architecture.
- Then: identify the cathode chemistry.
- Finally: assess the complete home battery system and the conditions behind every performance claim.
What the battery label tells you — and what it does not
A label can identify one part of a cell or product, but it cannot prove the performance, safety or suitability of the complete home battery.
No single label proves that a product cannot catch fire, has no thermal-runaway risk, charges faster, performs better below zero, lasts longer, suits every UK property or provides whole-home backup.
Semi-solid-state vs solid-state: a practical comparison
The practical difference is the electrolyte architecture, but a fair product comparison must go beyond the label.
Electrolyte structure: A semi-solid design may combine a solid or porous framework with a liquid or gel-containing phase. An all-solid-state design aims to use solid electrolyte materials as the ion-conduction pathway.
Interfaces: Both designs depend on stable contact between the electrolyte and electrodes. Interface degradation, cracking, void formation or local current concentration may affect performance and fault behaviour.
Production: Some semi-solid designs may adapt existing lithium-ion manufacturing methods, while all-solid-state cells may require different pressure control, material handling or interface treatments. This does not mean every semi-solid design is easier or cheaper to manufacture.
Evidence: Compare equivalent products using stated cell format, temperature, state of charge, charge and discharge rate, depth of discharge, cycle endpoint and safety-test method. A laboratory cell, automotive prototype and household battery are not interchangeable forms of evidence.
Why the cell is only one part of a home battery system
A homeowner buys an installed energy-storage product rather than an isolated cell. The electrolyte and cathode matter, but the battery pack, controls, power conversion, enclosure, protection, installation and support determine how the product works in the home.
Cells, modules and the battery pack
Cells store energy through electrochemical reactions. A home battery combines multiple cells into a pack, sometimes through intermediate modules, together with electrical connections, sensing, structural support and thermal pathways.
Pack construction can influence heat transfer, mechanical protection, serviceability and how a local fault may affect neighbouring cells. Cell-level data therefore cannot describe every characteristic of the assembled pack.
Battery management and power conversion
The battery management system, or BMS, monitors factors such as cell voltage, current and temperature. It can apply operating limits or stop charging and discharging when defined boundaries are reached.
The inverter or other power-conversion equipment manages the flow between the battery’s direct current and the home’s electrical system. Continuous output, peak output, grid-connected output and backup output must be assessed separately from battery capacity.
Energy control, enclosure and protection
An energy management system, or EMS, applies charging and discharging rules using available meter data, schedules, household demand and user settings. Its functions depend on the system configuration and compatible data sources.
The enclosure and protection design must also address electrical faults, overcurrent, short circuits, temperature and the intended installation environment.
Cell chemistry is only one layer of the product; this guide to how solar battery storage works explains the wider household energy flows and conversion paths.
Installation, warranty and support
Installation design affects product location, electrical protection, isolation, commissioning and the loads that can be supported. Warranty terms determine what is covered, for how long and under which operating conditions.
The IET Code of Practice covers the safe specification, design, installation, commissioning, operation and maintenance of electrical energy storage systems.
For domestic fire-safety context, PAS 63100:2024 covers small-scale BESS installation requirements including battery management, power-conversion equipment, fault management, location and protection against fire.
Does semi-solid-state automatically mean safer or better?
No. The label identifies an electrolyte approach, but it does not establish the performance of every cell, pack or home battery system.
Safety and thermal behaviour: Immobilising or reducing a flammable liquid phase may change fault behaviour in some designs, but the outcome depends on the complete electrolyte formulation, electrode materials, state of charge, cell format and test method.
Energy density and weight: Any improvement may also depend on cathode, anode, electrode design, inactive material and pack construction.
Charging and low-temperature operation: These claims require stated temperatures, charging rates, limits and test conditions.
Cycle life and lifetime cost: Compare depth of discharge, charge and discharge rate, temperature, state-of-health endpoint, warranty conditions and replacement assumptions.
A 2020 UK government review of domestic BESS safety considers cell failure alongside product design, system protection and installation measures intended to reduce the risk or impact of failure.
Please note: “Semi-solid-state” describes part of a cell’s design. The term alone does not prove safety, energy density, weight, cycle life, charging speed, cold-weather performance or suitability for a particular home. Compare the manufacturer’s definition, test conditions and complete system specification.
What should UK homeowners verify before buying?
Turn the technology label into a practical comparison by requesting evidence in four areas.
Semi-solid-state home battery checklist
Technology definition
Performance evidence
Complete system
UK purchase checks
What this means for UK home battery buyers
For UK buyers, the key question is not whether a product carries a semi-solid-state label, but whether the complete system is documented and suitable for the property. Check the installation route, power-conversion equipment, backup scope, protection design, warranty and local support.
Product certification and cell-level test results do not replace a competent system design and installation assessment. Confirm the intended location, electrical configuration, supported loads and applicable documentation for the specific product and home.
Explore Sunpura’s upcoming semi-solid-state home battery
Coming soon
Review the confirmed electrolyte architecture, battery chemistry, complete system specifications, warranty and UK availability on the product page when it launches.
Compare current solar battery storage options →Frequently asked questions
Sources and freshness
- Nature Communications research on a quasi-solid electrolyte in a lithium-metal pouch cell
- Faraday Institution SOLBAT solid-state battery research publications
- US Department of Energy lithium-ion technology assessment
- IET Code of Practice for Electrical Energy Storage Systems, third edition
- BSI PAS 63100:2024 for domestic BESS fire-safety installation
- UK government’s 2020 review of domestic battery energy storage system safety risks
Recheck the upcoming product terminology, UK URL, specifications, test evidence, warranty, launch timing and availability before publication.
