The Hidden, Wasteful Side of Electrification, and How We’re Fixing It (aka, Meet Little Timmy Who’s No Longer Sad)
Large batteries, or even not-so-large ones, are expensive assets. While the price is trending down, the erosion curve isn’t anywhere close to fulfilling our dreams of an all-electric future at a cost “too small to meter.”
The price of one raw kilowatt-hour of lithium-ion battery cells is between $100 and $200, assuming you buy them by the ocean liner load. About half of the cost goes into material sourcing, refining, processing, environmental mitigation, and hedging against the whims of the commodity markets.
The other half goes into manufacturing, plant investment and upkeep, labor, packaging, shipping, and integration. The battery pack for, say, a forklift, costs thousands of dollars — and you can’t do much to reduce the cost substantially.
Yet, batteries aren’t used as efficiently as they should, like other expensive assets. We have written and spoken about this extensively in our blog posts. The simplest way to reduce the cost of electrification is to increase the utilization rate for every pound of lithium.
Making bigger batteries won’t solve the barrier to democratizing electrification. To increase utilization and lower costs, you must make every cell in a battery work harder and longer to maximize resource usage.
Of course, it’s not good to have battery packs sit idle. But that’s just the obvious stuff. We like to look for trickier problems to solve. What can we do with a battery pack still in active use but is getting a little older with slowly deteriorating performance?
Some battery packs have a dozen or so large prismatic cells, while others contain thousands of smaller ones. Sometimes the performance gap between the best cells in a pack and those with the most deterioration is small. Sometimes it’s significant.
The older the pack, the bigger the delta. The more extreme the temperature exposure, the faster the performance deterioration. But one thing we know for sure: The pack capacity and peak discharge current are only as good as the weakest link — the cell with the most deterioration (aka, little Timmy).
Let’s go back to the forklift’s battery pack. After years of diligently lifting pallets, the battery indicator says it has lost 50% of its capacity. Or has it?
A much more likely scenario is that little Timmy wears out faster than others. But most other cells could still be close to design capacity. However, in almost all traditional battery designs, the entire battery pack can no longer store energy beyond the 50% mark if one cell or module loses 50% of its capacity because the cells or modules are wired in series. A similar phenomenon occurs for other parameters like peak discharge rate and internal resistance.
So you may have a 15S (15 series connected cells) forklift battery pack where 14 cells are at 99%, but little Timmy is at 50%. The resulting battery pack can only store 50% of its original capacity. If you don’t like that, you’d have to throw out the baby with the bath water. What a waste (and bad for the environment)!
Here’s another example: The internet has numerous stories about early-generation Tesla Model S cars with dead batteries. Tesla only replaces entire battery packs at eye-watering prices, making repairing its cars economically unfeasible.
Unsurprisingly, an entire cottage industry has sprung up to crack open these still-mostly-good battery packs and replace only the little Timmies. The result is a rejuvenated electric car, saved from its unglamorous end at the crusher, for a couple of thousand dollars.
But we thought, “What if instead of finding a solution to repairing deteriorated cells, we prevent the issue from happening as much as possible, and if it happens, resolve it automatically?”
We invented the Tanktwo Battery Operating System (TBOS) to address the challenge. The system not only prevents premature (or even mature) capacity or performance deterioration. Even when cells have deteriorated, the system makes them work at their maximum capacity and keeps the output consistent without fixing the little Timmies.
Gone are the days when one cell or module in the chain dictated the whole pack's performance. But how does it work?
A TBOS pack has more series connectable elements (cells or modules) than needed to reach the required system voltage. For example, it would have 12 if you need 10. During operation, 10 of them are active at any given time, with all cells taking turns.
A weighted round-robin allocation method determines which cells will work when and how hard. A cell will operate 50% of the time if it has only 50% of its design capacity left. Meanwhile, the best cells in the pack will work much closer to 100%.
As a result, a cell that has lost a percentage of its capacity, whether it’s 2% or 80%, will still contribute to the system as much as it can. As a result, we can fully utilize any cell in a system — reducing wastage, the environmental impact of electrification, and the hot potato second-life problem.
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