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QuantumScape
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== Solid state lithium-metal technology == '''Advantages versus conventional lithium-ion batteries''' The current state of conventional lithium-ion batteries is known to pose limitations on range, density, life cycle, charging speed, and safety. For instance, today’s Panasonic 2170 NCA (nickel cobalt aluminium) cells are estimated to have a battery density of ~270Wh/kg to 300Wh/kg. Batteries with higher Wh/kg could store more energy (watt-hours) per unit of mass and helps address range anxiety which is known to be one of key challenges in EV adoption. Shown in the exhibit below, a conventional lithium-ion cell has a cathode layer (positive electrode), a porous separator usually made of polymers, and an anode (negative electrode) that’s usually composed of graphite or silicon, liquid electrolyte, as well as current collectors (foils, tabs) on both the anode and cathode ends. The liquid electrolyte saturates the cell, including in both the anode and cathode, and during charging and discharging, lithium ions become suspended in the electrolyte and move toward the opposite electrode through the polymer-based separator. While the design, size, and use cases vary from one lithium-ion cell to another, a critical factor is the stability of the liquid electrolyte which are usually made of hydrocarbons. Lithium-ion batteries have specific temperature conditions under which they perform the best in cycle life and efficiency. When operating above a certain temperature, lithium can melt and react with the liquid electrolytes to cause a fire explosion. Even if the external environment might be cool enough, the battery can still heat up internally, leading to thermal runaway. On the contrary, when operating at extreme low temperatures, the ions move slower through the liquid electrolytes, resulting in a capacity reduction. Additionally, low temperatures can cause the velocity of the ion transfer to decrease, which can make it difficult to charge a battery. These specific challenges represent some of the problems QuantumScape is looking to solve, by using pure lithium-metal and solid-state separators without liquid in the composition. While lithium-metal itself as an anode has been researched for several decades, it has also been known to react in unstable ways with liquid electrolyte. Thus, current technology needs to incorporate a solid separator which can help resist dendrite formation. QS is essentially looking to solve these limitations, by replacing the porous polymer separator with a solid ceramic separator and removing the anode. The cell is then left with a two-layer battery (only a cathode and a separator). The anode forms in-situ when the battery is charged for the first time in the factory; liions leave the cathode, through the separator, deposit themselves on the other side and creates a layer of solid lithium metal. Then it cycles back and forth. Such design would bring about benefits including higher energy density, faster charging, lower cost (about 15%-20% less thanks to the elimination of the anode material and manufacturing cost), increased battery life, and better safety. So far, QS’ data shows its testing cells’ ability to charge from 0% to 80% in 15 minutes and from 10% to 80% in 12 minutes. Typically, without solid lithium-metal anode, battery density typically doesn’t rise above low 300s in Wh/kg; QS expects development in this technology is to raise energy density by 50-80%, to +400Wh/kg or more, while costing 15% to 20% less to lithium-ion equivalents. '''Development stages (single to multi-layers)''' The immediate and mid-term challenge ahead for QuantumScape is forming multilayer cells and from there on, scaling up the manufacturing process. The company’s development approach is to build a single layer platform based on which QS validates the core chemistry capability and establish key performance parameters including charge rate, cycle life, temperature, and pressure. Post the single-layer validation, QS has moved on to a 4-layer then 10-layer, and now working towards 16-layer with ultimately dozens of layers in cell testing. In the next-gen battery technology space, unlike in the automotive, the fundamental chemistry has been the big problem. From a manufacturing perspective, no new laws of physics need to be invented. However, the chemistry is very much fundamental and serves as the building block, but completing a prototype is not as easy when compared to building a vehicle prototype (assembly), given the need to test in real-world and uncompromised conditions. Once QS progresses towards the 16-layer testing, the next step is several dozens of layers of testing which would then position them to provide A-sample prototype to its OEM customers (targeted for end of the year to at least one OEM customer). '''Technology differentiation vs. other next-gen battery players''' In the last couple of years, several startups focused on developing next generation batteries have become public, with notable ones being QuantumScape, SES, and Solid Power. Technology differentiation and viability is often difficult to assess from the outside, given the lack of actual mass-scale production and real-world performance data in EV fleets. These companies are taking different technical approaches in trying to improve batteries density, safety, cycle life, and cost. QS’ approach is predicated on the elimination of anode layer and the introduction of a ceramic-based solid separator to replace the polymer-based separator. According to the company, the separator has two attributes that make it highly manufacturable; First, its components are earth-abundant commodities and are already being used at scale. Second, the separator manufacturing process itself should work with continuous flow; tape casting and heat treatment are the two steps required for making a ceramic and QS can do it continuously. Separately, QS is designing the cells to be cathode agnostic, thus the company can use NMC or LFP chemistries. In fact, QS states that the LFP version of its batteries should have near equal energy density as today’s NMC batteries, with lower cost and competitive performance. On the other hand, SES has announced that it is dropping its efforts towards true solid state and pivoting to a hybrid lithium metal solution for faster manufacturability, which the company names via three developmental tracks: Hermes, Apollo, and Avatar. Hermes is a small battery roughly the size of an iPhone, and the difference from QuantumScape’s approach is that SES is introducing a proprietary solvent-in-salt liquid electrolyte and composite anode coating to help increase safety and cycle life vs. a conventional lithium-ion battery. The cathode stays the same; and an ultra-thin layer of li-metal anode is manufactured through SES’ proprietary process. Apollo is a version of Hermes that is about 25x bigger, designed specifically for automotive applications. SES has said it’s currently ramping up anode coating and cell manufacturing quality and testing capabilities for A-samples in its Shanghai and Korean factories. Lastly, through Avatar, an AIpower software that monitors battery health, the company hopes to predict 100% of potential safety incidents. Furthermore, the way SES looks to solve the dendrite challenge is to slow down dendrite growth and change the shape of its formation (from sharp spikes to round) and detects safety issues early, whereas QS is deploying a solid-state separator with high dendritic resistance. Solid Power, for a while, has been working on lithium metal batteries but over the course of the last 6-9 months the company shifted focus to silicon anodes. While it’s not entirely abandoning lithium-metal, Solid Power cited one of the challenges it faced with lithium metal is delivery of high rates of charge given the tendency to form dendrites that could short circuit the cell. While the company aims to solve for this challenge as a second step, it is pursuing a high-content silicon anode solution in the nearest term with the use of its core technology: sulfide-based solid electrolyte, as well as solid anolyte and solid catholyte. Other non solid-state battery companies pursing the high silicon anode strategy include Enovix and Sila Nanotechnologies. Currently about 99% of lithium-ion batteries in use have anode material made of carbon (in the form of graphite), but transitioning to silicon would be a better choice given that it holds 10x more lithium than graphite. Silicon-based materials also generally have a much larger specific capacity. For NCM/NCA cells, switching to silicon-dominant anodes could potentially boost energy density by 50%. However, one of the key disadvantages is that when silicon reacts with and absorbs lithium ions, it swells by 300% (vs. 7% for graphite), and this intense swelling eventually damages the silicon, causing its surface to crack and energy storage performance to drop rapidly. On the other hand, lithium-metal anodes don’t present an expansion problem, but they are expensive and present other technical challenges. Sila Nanotechnologies, for example, is looking for ways to resolve the aforementioned swelling problem in silicon anodes, and if successful it could represent significant opportunity to improve the performance of existing li-ion batteries. Silicon is indeed among the world’s most abundant elements, and if cell makers eventually transition to silicon anodes, there will be meaningful benefit associated with exploring better cathodes given silicon anodes’ expanded ability to store.
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