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Higher-Density Solid-State Battery Technology

Last year we took a look at Infinite Power Solutions (IPS), one of a couple of companies that have commercialized a solid-state lithium ion battery technology licensed from Oak Ridge Labs. Their current offering (pun intended) focuses on thin, flexible cells. But they have just announced a new technology, and at this point, it’s only a technology; they haven’t released any information on how it will be productized (and they may still be figuring that out).

The upshot is what they claim to be record energy density: 1000 watt-hours per liter. This density for a 4-V rechargeable battery in a small size is a combination that they say doesn’t exist today – OK, well, it exists today, but not before this announcement. For comparison, cell phone batteries have around 400-500 Wh/l.

Unlike their existing micro-energy cells (MECs), which use thin films, these new high-energy cells (HECs) are thicker (1 mm), involve ceramics, and do include some organic materials – which they claim to be very “dead” or inert, like Teflon. In other words, they would still be safe to put in the trash.

The details of the chemistry haven’t been disclosed.

  • The anode in particular is secret – it becomes metallic when the battery is charged.
  • The electrolyte is a solid-state composite of polymers and inorganic materials.
  • The cathode is the same as used in the MEC (and possibly other batteries); the trick is how it’s deposited and… something else. A secret ingredient or step.

They say that it operates much like a hybrid metallic/ion battery. But because the electrolyte is a solid, not porous like standard cell phone batteries (because it needs to absorb the liquid electrolyte), it’s denser, contributing to the higher energy density. HECs, like the MECs, also lack the mechanism that proved over-dramatic in laptop batteries in the past – the risk of little metal shards plating out and shorting out the battery.

The charging will be a bit more complex than that of the MEC, but they’re trying to keep to the constant-voltage charging approach, which is simpler that the more traditional constant-current/constant-voltage process. They’re still working on endurance; they’re at 20 cycles now, moving to 50 (for reference, cell phone batteries are in the 500-800-cycle range, although the wear-out mechanisms are different). They are still evaluating whether they’ll be able to get to 200.

Of course, in an energy-harvesting application, where you discharge only a little and then trickle back up, the number of recharge cycles goes way up. A rule of thumb is that the cycles increase by the inverse of the depth of discharge (DoD). So if you get 50 cycles with 100% DoD (draining all the way), then you would get 1000 cycles with 5% DoD (20x).

They identify two other benefits of being solid state: long shelf life and the fact that the battery housing doesn’t need to deal with gases and vapors as a part of the charging/discharging process.

Today, IPS and Cymbet are the two companies that have made a go of the Oak Ridge technology. But they’ve addressed different spaces: IPS with thin, flexible cells less than 2.2 mAh; Cymbet with silicon-based, small (even bare-die) cells from 1 to 50 mAh. With this increase in density, using a technology that isn’t amenable to a flexible cell, it seems that IPS may start encroading on what has been Cymbet’s turf. In fact, they foresee 150-mAh cells.

But no date was given as to when the HEC technology will be productized. So we’ll keep an eye out for it.

You can get more details in IPS’s release.

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