Amprius Technologies manufactures lithium-ion batteries with the industry’s highest energy density cells. Their corporate headquarters is in Fremont, CA, where they maintain an R&D lab and a pilot manufacturing facility.
Amprius boasts a cash runway of approximately three years, enabling it to finance its growth plans and develop its technology. Furthermore, other assets may aid Amprius’ efforts.
Silicon Nanowire Anodes
Silicon has long been considered an attractive anode material for lithium-ion batteries due to its high specific capacity, superior electrical conductivity, and lower cost than graphite anodes1. Unfortunately, commercialization has been prevented by their morphologic instability during cycling, which results in extreme volume fluctuations, pulverization, rapid capacity decline, and fast capacity loss1.
Recent efforts have aimed at reducing particle dimensions to address these issues, with promising results from Si nanostructures such as pomegranate-shaped nanoparticles (NP)8,9, spherical Si nanowires (SiNW)10-13 and porous Si/graphene composites14 showing encouraging signs. Unfortunately, their practical applications remain restricted due to complex production methods and lower cycle performance than commercial graphite products.
Researchers have created a scalable method for fabricating high-aspect-ratio SiNW anodes using cryogenic ICP-RIE, optimizing five critical parameters – temperature, O2 content, pressure, RF power, and ICP power – in the etching process to achieve verticality, length and sidewall angle with good verticality and length dimensions. Controllable sidewall profiles also play an integral role in optimizing the electrochemical properties of anodes; for instance, a perpendicular sidewall profile helps decrease volume expansion lithiation/delithiation rate significantly.
By carefully controlling process parameters, researchers were able to create SiNWs with sidewall angles of 90deg or greater, coated in NiSix as buffer layers to suppress mechanical pulverization and enhance reversible cycling performance by providing space for expansion during lithiation/delithiation cycles. Furthermore, their improved morphology and buffer layer design contributed to low self-discharge of anodes that remain stable over 300 cycles at 2C with high capacity retention in pouch cells.
The authors further characterized these electrodes by performing X-ray and TEM analyses. Their researchers determined that their reversible cycling behavior can be explained by their spherical shape and high surface-to-volume ratio while having lower diffusion distance for lithium ions that contributes to their high reversible capacity and excellent electrical conductivity; all factors which allow SiNW anodes to compete with commercial graphite anodes for high rate applications.
Lithium-Ion Batteries
Lithium-ion batteries have become the go-to battery choice for mobile electronics, electric vehicles, and grid energy storage systems. Their success in portable electronics comes from their superior gravimetric and volumetric energy densities compared to rechargeable systems that rely on aqueous electrolytes.
Li-ion batteries consist of a cathode made of lithium iron phosphate, nickel manganese cobalt, or other lithium metals and an anode of graphite. At the same time, their performance depends on the conductivity of active materials and high cell integration levels. Recent research indicates that graphene-based nanomaterials provide superior conductivity and stability compared to current cathode materials, further increasing overall lithium-ion cell performance.
Batteries constructed of these materials are compact and lightweight with rapid recharge times, making them suitable for backup power in case the mains electricity supply goes out or for applications that do not rely on constant electrical energy; for example, surveillance cameras, remote monitoring of fleet vehicles or job sites and medical equipment that requires instantaneous power.
Lithium-ion batteries are an integral component of modern electronic devices but have drawbacks. Due to their highly flammable electrolytes, lithium-ion batteries must be handled with extreme care and adhere to more stringent testing and safety regulations than other rechargeable battery types. Furthermore, when damaged, they can quickly pressurize and explode.
Though challenges may be involved with designing and manufacturing batteries, ongoing research to enhance their design and performance – particularly energy density – continues. Researchers use surface coatings, electrolyte additives, and morphology optimization techniques to increase the voltage as close as possible to the fundamental limits. Limiters occur when further lithium removal causes irreversible structural transformations or oxygen loss at the cathode or if no vacant spots remain on anodes to accept more lithium ions.
If your device contains batteries, recycling them at the end of their useful lives rather than disposing them in household trash or recycling bins is essential. The EPA suggests finding a local location where recycling can occur; when shipping these materials, they should be treated as Class 9 miscellaneous hazardous material requiring unique markings and paperwork.
Silicon Nanotube Cathodes
Lithium-ion batteries rely heavily on their electrodes for proper functioning. Researchers are developing a silicon anode that is capable of holding more lithium and charging faster than graphite used in traditional battery electrodes – up to 10x more lithium can be stored, and five minutes recharge time instead of the day required by graphite anodes; plus, it is less prone to structural failure such as cracking or disintegrating and can last through more cycles than traditional graphite anodes.
The PNNL team developed a scalable process for etching porous silicon anodes. By employing this technique, they could produce anodes with micron-sized pores that allowed more surface area to be exposed during charging and discharging cycles. Furthermore, they designed an electrolyte specifically tailored for silicon anodes which reduced leakage current while increasing cycle life.
Scientists employed carbon nanotubes to enhance the performance of silicon anodes for lithium-ion batteries. By adding them without significantly increasing cost or complexity, carbon nanotubes were successfully integrated between silicon particles to increase the surface area available for lithium insertion/removal while stabilizing the charging/discharging of anode material by preventing its outer surface from expanding as it absorbs lithium which would otherwise degrade an electrode’s performance.
The hybrid silicon-nanotube anode developed can deliver very high capacity with meager resistance, maintaining its energy density for an extended cycling lifetime and charging up to 20C. The research team is currently optimizing anode material for commercial use and hopes it will enable lithium-ion batteries with much higher energy density than current technology. This new anode material could eventually produce battery cells with five times more power than those found in cell phones today, as well as ultrafast charging capabilities to provide fast battery recharging solutions suitable for mobile devices and other applications that demand rapid battery recharges.
Lithium-Ion Electrolytes
Electrolytes are an integral component of lithium-ion batteries. They separate positive and negative electrodes within your battery so lithium ions can pass between them, creating an electrical potential difference that powers electronic devices. A thin layer of insulating material known as a separator sits in the electrolyte solution between anode and cathode terminals to prevent short-circuiting during charging; during discharging, they return through it via their separation layer back through to their source electrode, telling you how much charge remains in your battery.
Today’s lithium-ion batteries utilize liquid, gel, or dry polymer electrolytes that combine an organic solvent (typically ethylene carbonate) with a salt solution containing lithium and other metals to form their electrolyte solution. To increase chemical and thermal stability, these electrolytes may be filled with additives to modify the properties of their gel structure by altering oxygen availability for the ionic aggregates forming, resulting in conductivity variations.
Another effective strategy for increasing electrolyte conductivity is using high-molar mass polymers. When dispersed into low-temperature molten salt solutions, these polymers form rubbery material with lower glass transition temperatures than its crystalline counterpart. Furthermore, polymer electrolytes often boast superior ionic conductivity due to having more ion pairs coordinated with solvent molecules than their counterparts.
Researchers are exploring semi-solid or quasi-solid ionic liquids as an additional solution to improve polymer electrolyte durability for lithium batteries, hoping to provide improved durability over conventional organic liquid electrolytes. Such electrolytes may form into a gel when plasticizer is added, giving conductivity comparable to organic liquid electrolytes while offering mechanical and chemical stability – possibly helping alleviate slow cycling issues associated with lithium-ion batteries; furthermore, such materials should also be compatible with cathode materials commonly found today such as graphite or silicon.
