In our summer issue, Frank Lev explored wet and dry battery electrode (DBE) technology. Global battery OEMs are actively pursuing the development of DBE technology, he noted. But Christian Dietrich, director of business development at energy storage nanotechnology innovator Nanoramic, argues that in fact it is not entirely proven and the jury is still out on dry battery electrode technology.
Dry battery electrode (DBE) technology is often seen as a potential disruptor in lithium-ion battery manufacturing. However it faces challenges in upscaling and the claimed benefits may not be proven in series production applications. Meanwhile, wet battery electrodes (WBE), the current industry standard, are expected to electrify the automotive sector and scale-up significantly in the following years.
Manufacturers have struggled to validate DBE potential, and ambitious claims such as Tesla’s 4680 battery cell, promising substantial cost reductions and a 10-fold carbon footprint reduction through DBE, remain unproven. Therefore, optimising WBE technology to address its current constraints seems a more feasible path, especially when considering the equipment upgrades, factory overhauls and fundamental challenges that DBE entails. These have the potential to hinder its performance, cost-effectiveness, and sustainability benefits.
While DBEs hold potential for higher energy density by accommodating thicker layers (~50–100 microns), a large amount of polytetrafluoroethylene (PTFE) binder is required, impacting cost and carbon footprint. Also, these DBE thick coatings are susceptible to web breaks due to their free-standing coating process. On the other hand, challenges arise in achieving thinner coatings, which are important for rapid-charging electric vehicles (EVs), especially when silicon is present in the anode, since PTFE cannot accommodate its large volume expansion.
WBEs offer a flexible solution, meeting EV requirements with coatings of 60–90 microns. However, binder migration, extended drying times, and surface cracking limit their coating thickness and ultimately, their areal capacity. Additionally, they present a trade-off in power that comes with thicker coatings. Many of these challenges can be addressed by eliminating polyvinylidene fluoride (PVDF binder) and the related need for N-Methyl-2-pyrrolidone (NMP solvent) from the WBE process.
Nanoramic’s Neocarbonix WBE technology successfully replaces PVDF with an electrically conductive carbon binding structure. By removing PVDF, Neocarbonix also eliminates the need for NMP, which is required to dissolve PVDF in the slurry during conventional WBE manufacturing.
Instead, Neocarbonix uses water or alcohol solvents, which afford a number of benefits including a reduced risk of cracking (alcohol only) during drying – especially for thick coatings, reduced drying energy consumption, and better environmental friendliness. This also enables electrodes that can accommodate a wide range of thicknesses, from standard WBE to DBE levels (up to 200 microns).
Energy density and power
Tesla’s 4680 cells set a benchmark with energy densities of 244–283Wh/kg using a dry battery anode, which surpasses most currently available EV technology. But while DBEs offer potential for higher energy density through thicker coatings, they also compromise power and therefore charging capability due to higher areal capacities.
Conversely, WBEs excel in high-power scenarios, favouring faster charging. Neocarbonix combines the benefits of both, offering high-energy cells with thick cathode active layers, and robust silicon anodes using its carbon binding structure, while catering to high-power demands due to its high electrical conductivity and low tortuosity.
Binder choice significantly affects battery electrode performance and sustainability because they impact the lithium-ion conduction pathways as well as battery carbon footprint. DBEs aim for lower binder concentrations of around 1% PTFE, but often require closer to 2%. Fraunhofer states 3% PTFE to prevent web breaks and attain thinner coatings.
In contrast, WBEs use about 2–3% total inactive materials, including 1–1.8% PVDF binder, along with non-fluorinated carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) binders on the anode. Neocarbonix reduces inactive materials in WBEs, for example NMC (nickel-manganese-cobalt) batteries, to about 1%, resulting in an approximate 99% active material cathode.
Sustainability: environmental impact matters
DBEs and WBEs both face environmental and regulatory challenges because they rely on PTFE and PVDF. The carbon footprint of PTFE is significantly higher compared to PVDF: Joscha Schnell of P3 automotive claims PTFE is 143.7kg CO2e/kg compared to 8.5kg CO2e/kg for PVDF.
But both substances are PFAS, a class of chemicals pending regulation from the US Environmental Protection Agency and European Chemicals Agency. Additionally, they are both difficult to separate from battery materials during recycling, and the presence of fluorine is known to generate damaging and highly corrosive hydrofluoric acid during the recycling process.
The carbon footprint of WBEs can be significantly reduced by addressing the drying stage of manufacturing. A paper last year in the journal Matter (Dry electrode technology, the rising star in solid-state battery industrialization) stated this accounts for about 47% of manufacturing energy consumption.
Conventional WBEs are difficult to dry due to their use of NMP, which has a high boiling point and low vapour pressure. By removing PVDF and therefore, the need for NMP, Neocarbonix enables a more efficient drying process, resulting in a 25% reduction in the cells’ carbon footprint. It also improves recycling by eliminating fluorine from the process, and by enabling non-NMP solvent dissolution, e.g. in water or alcohol.
The cost factor
DBEs pose a cost challenge due to their need for current collectors that are twice as thick as those used with WBEs. Notably, DBEs require a wet-coated primed foil, offsetting the advantages of being a dry technology. DBEs are estimated to lower CAPEX, OPEX and CO2 for the drying process by 35%, 50% and 65% respectively, but P3 Automotive’s Schnell argues the total cell cost may still be increased by 1% due to the high cost of PTFE and primed foil. Additionally, DBEs add at least 0.5–1% scrap due to the necessity for edge removal arising from the ragged edges created during the dry coating process.
WBEs have potential for significant reductions from their current benchmark of about $115/kWh if Neocarbonix technology were used. At the same time, Porsche Consulting research for Nanoramic stated that cell costs can be cut by up to 27% and CAPEX by 25%, and production capacity boosted by 30%.
This is possible through the previously mentioned reductions in energy consumption and the amount of inactive materials in a battery cell, therefore improving efficiency and reducing cost per kWh. Neocarbonix also increases throughput by 50% on the coating lines due to the higher electrode loading.
Adaptability: the key to integration
DBEs demand a substantial investment from battery manufacturers due to the need for entirely new production equipment. Given that WBEs currently serve as the manufacturing standard, they offer significant advantages to manufacturers who can achieve battery optimisation using their existing production lines: a possibility made feasible through the use of Neocarbonix.
In the pursuit of the ideal battery electrode technology, the landscape remains multi-faceted as each technology offers unique advantages and trade-offs. While DBEs show promise, they grapple with cost, thickness, adaptability, and sustainability challenges. Neocarbonix technology emerges as a transformative solution by further optimising commonly used WBE technology, while at the same time addressing and overcoming many of these issues.