What are QuantumScape’s Anode-Free Batteries and how do they work?
With companies like Tesla and QuantumScape making major headlines in the race to produce the best new battery on the market, it’s hard not to be excited about the future of energy storage. One of the highlighted technologies starting to make its way out of the lab are so-called ‘anode-free’ cells, a potentially game changing alternative to the graphite anodes used in conventional lithium-ion batteries. But what are anode-free cells and how do they work?
First, how do lithium-ion batteries work?
In a conventional lithium-ion battery, materials are carefully layered together in a way that permits a current to flow from one side to the other as the battery is charged and discharged. On one side of the electrolyte, an aluminum current collector and positive electrode (cathode) made of a lithium-rich blend of materials including cobalt, nickel, and manganese are layered together. On the other side, a negative electrode (anode), usually made of graphite is layered alongside a copper current collector.
As the battery is charged, lithium ions are pulled from the positively charged cathode and stored in the anode. When the battery is discharged, the lithium ions are released in the opposite direction, powering the device to which they are connected.
Source: Planete Energies
Conventional lithium-ion batteries continue to dominate the field for both their reliability and cost competitiveness, however limited power density and cycle lifetime has led researchers to look for solutions beyond the existing technology. Alongside performance limitations, another critical issue needing to be overcome is the highly reactive nature of lithium metal, which can be incited in batteries through the formation of small structures called dendrites. When these dendrites form, they can grow large enough to puncture cell layers, causing the battery to short-circuit and eventually catch fire. Both of these issues look to be solved by anode-free/lithium-metal solid-state batteries while decreasing cost for manufacturers.
So what are anode-free batteries?
In an SEC filing last month, QuantumScape introduced its lithium-metal battery architecture that looks to have overcome the safety and performance challenges of lithium-ion batteries through the implementation of an anode-free design. While the name suggests these cells don’t use an anode, in actuality, their clever architecture means that they are only ‘anode-free’ upon assembly at the manufacturer. (See diagram)
Source: SEC
Rather than including a conventional anode electrode made of graphite or silicon, only a porous separator sits between the electrolyte and current collector when the cell is produced at the factory. As the cell charges for the first time, lithium-metal ions are actively deposited onto the current collector, which acts as the anode from then onward.
Source: Nature Energy
What are the advantages of anode-free architectures?
One of the most significant advantages of anode-free cell designs is that they alleviate the need for manufacturers to produce thin lithium foils that are costly and difficult to process, meaning a potentially much cheaper alternative to conventional lithium-ion batteries. Moreover, while lithium-metal cells do not necessarily need to be anode-free, they demonstrate substantial energy density improvements over conventional anode materials like graphite. (See below)
Source: Energy Science & Engineering
Beyond the energy density improvements over conventional lithium-ion, QuantumScape’s anode-free cell design has also demonstrated impressive cycle life, with tests highlighting the equivalent of 800 thousand kilometers for an 800 kilometer battery pack using their cells. While Tesla has been promising the potential of a million-mile battery for some time now, QuantumScape looks like it could make a formidable competitor in the near future.
The potential of these anode-free architectures hasn’t been out of the EV giant’s sights however. In 2020, Tesla’s Canadian research lab, headed by Jeff Dahn, submitted a patent for lithium-metal/anode-free cells. Taking a slightly different direction than QuantumScape, Tesla’s cells do not make use of a solid electrolyte. By no means do patent applications guarantee these batteries will ever reach a commercial production line, QuantumScape’s published performance results demonstrate promising advantages in energy density, cost, and cycle life (Elektrek).
Source: QuantumScape
While it will likely be a number of years before we see vehicles on the road powered by anode-free batteries, the technology is certainly one of the most intriguing innovations to have emerged in recent years and we’re looking forward to following its development.