Today, shortly after receiving an award from the Cleantech Group for North American company of the year (yet another kiss of death), Aquion declared bankruptcy.

Aquion raised a total of $190 million in venture capital and debt for its saltwater batteries intended for long-duration storage. The company also raised a lot of hype.

The startup just "filed a voluntary petition under Chapter 11 of the United States Bankruptcy Code in the United States Bankruptcy Court of the District of Delaware. Immediately preceding the Chapter 11 filing, the Company retrenched to a core R&D team by terminating approximately 80 percent of its personnel (several of whom have also entered into consulting agreements with the Company to assist it in the sale of its assets), paused all factory operations, and stopped the marketing and selling of its products."

After spending $190 million and making bold promises, outgoing CEO Scott Pearson had this to say:

"Creating a new electrochemistry and an associated battery platform at commercial scale is extremely complex, time-consuming, and very capital-intensive. Despite our best efforts to fund the company and continue to fuel our growth, the Company has been unable to raise the growth capital needed to continue operating as a going concern."

"In the coming weeks, Aquion will be working to secure a bidder to purchase substantially all of its operating assets."

Having an impressive list of investors just doesn't translate to market success. Aquion's investors included Bill Gates, Gentry Venture Partners, Kleiner Perkins Caufield & Byers, Foundation Capital, Bright Capital, Advanced Technology Ventures, Trinity Capital Investment and CapX Partners, Yung’s Enterprise, and Nick and Joby Pritzker.

Bill Gates is also an investor in LightSail Energy, the challenged compressed-air startup, and Ambri, the liquid metal battery project from MIT professor Don Sadoway.

Not so long ago, the company told GTM's Stephen Lacey, "The Aquion business and the energy storage market continue to develop well. The funds will support continued scaling of the business, the expansion of our product offerings, and new customer deployments worldwide.”

Aquion's sodium-ion battery was designed for multi-hour applications. According to the company, its batteries could deliver a round-trip efficiency of 85 percent and perform 5,000 cycles. The company's cost target was $250 per kilowatt-hour, with the goal of getting to $160 per kilowatt-hour.

While short-duration lithium-ion batteries are dominating the market, investors are increasingly interested in batteries that can discharge over long periods of time.

As Jeff St. John reported last year, Aquion supplied "what could be the biggest battery ever ordered up by a private citizen" -- a 1-megawatt-hour system, backing up the residence and working farm of Medtronic founder Earl Bakken. And Aquion just announced a microgrid installation at an organic winery and farm in Sonoma, Calif. that combines fourteen 25-kilowatt-hour Aquion batteries (approximately 350 kilowatt-hours of energy storage) with a 30-kilowatt power conversion system from Ideal Power and a 32-kilowatt solar system.

Ravi Manghani, director of GTM Research's energy storage practice, writes: "Energy storage is not for the faint-hearted. Aquion's claim isn't entirely incorrect -- it was furthest along among the emerging storage technology cohort, with proven technological capabilities. But as has been the case in the storage technology space, lithium-ion battery costs have fallen so rapidly (over 50 percent in the last three years) that a lot of cost roadmaps for challengers have been thrown off-track. The only way for emerging storage technology startups to stay relevant is to scale quickly, which of course requires huge amounts of capital."

"As for Aquion's chances of finding a suitable buyer, I wouldn't be surprised if it finds a good strategic buyer that's entrenched in the off-grid or microgrid business, both of which would be a good market fit for Aquion's chemistry."

David Snydacker, a battery expert at Dosima Research, tells GTM: "Aquion's size/weight per kilowatt-hour was approximately 15-times greater than lithium-ion. Like other competitors to lithium-ion, Aquion tried to emphasize that size/weight doesn't matter for grid storage. But all that extra material has an associated cost. The bankruptcy was probably foretold by the bill of materials."

Investor Vinod Khosla has funded a number of energy storage companies including Pellion, LightSail, QuantumScape and Seeo. There are a number of other companies developing lithium-ion alternatives. Eos has a zinc-air battery with some customer traction. In 2014, Alevo unstealthed with claims of a new sulfur-based inorganic lithium-ion electrolyte chemistry. Stanford University technology can be found in Huggins Group battery startup Alveo Energy. Fluidic Energy is deploying zinc-air batteries.

Dozens more startups are aiming for utility-scale energy storage working with compressed air, mechanical systems, flow batteries, and other electrochemical means.

Getting an entirely new and novel battery chemistry to commercial scale remains Sisyphean work. There is a load of VC investment thinly spread in this field -- and a dismal, all-too-familiar reckoning awaits.