Exploring the Possibility of Lithium-Titanate (LTO) Batteries for Toyota Prius: Lessons Learned

Over the years, many people have asked me about the feasibility of using lithium-titanate (LTO) batteries as a hybrid power source for the Toyota Prius. After much research, experimentation, and real-world testing, I want to share my findings here. Hopefully, this can save DIYers some time, effort, and money.

As of 2024, LTO batteries are still among the strongest lithium chemistry variants available. They boast an impressive cycle life of over 10,000+ cycles and are designed to handle high charge and discharge currents—qualities that make them appealing on paper. However, there are some significant drawbacks you should know about before diving in:

1. Cost
   LTO batteries are very expensive. If regular lithium batteries weren't pricey enough, adding titanium to the mix drives costs even higher. In 2023, I tried negotiating with some of the last remaining LTO manufacturers in China, but even bulk orders didn’t bring prices down to a reasonable level.
   
   
2. Weight
   LTO packs are heavy. This is because LTO cells operate at a lower voltage range (1.8V–2.8V per cell), meaning you need more cells to power a hybrid system like the Prius. This added weight can impact the overall performance and efficiency of the vehicle.
   
   
3. Charging and Discharging Characteristics
   LTO batteries have a very sharp charge/discharge curve. This means they can suddenly run out of power or reach full charge without much warning—a trait that doesn’t pair well with the Prius hybrid system. If you’ve followed my journey with the failed Project Lithium, you’ll know exactly what I’m talking about.

Back in 2019, when we were just starting to explore batteries and had little knowledge about them, we attempted to assemble an LTO pack. We used a total of 98 Toshiba 3Ah LTO cells, thinking their long cycle life would make up for the low capacity. Unfortunately, we quickly learned that this was not the case.

The pack lasted only about an hour. The sharp charging curve, combined with the low capacity, didn’t give the Gen 2 Prius enough time to properly stop charging. As a result, most of the cells puffed up, rendering them unusable. After spending nearly $2,500 on materials, we had no choice but to scrap the project.

Toshiba 3Ah LTO assembled and installed to a Gen2 Prius:



Fast forward to late 2022, we decided to revisit LTO technology while exploring alternatives to LiFePO4 chemistry. This time, we assembled three new LTO packs using two different LTO cells from Sheng Quan. Here are the models we used:

• QT-32145H-6Ah
• QT-32145H-10Ah

10Ah LTO in a 7S configuration prior to assembly:


10Ah LTO in a 7S configuration with wire harness installed, prior to assembly:


10Ah LTO assembled and installed in a Gen3 Prius:


10Ah LTO assembled and installed in a Gen3 Prius:


10Ah with active balance board installed:


6Ah LTO assembled:


6Ah LTO assembled with a active balance board and installed in a Gen2 Prius:


Gen2 Prius with 6Ah LTO:


We initially ran all the LTO packs without a balance board. After a few months, we noticed the block voltages began to drift apart. To address this, we prototyped a custom active balance board designed to dissipate extra power base on neighboring cell's voltage. This immediately resolved the block voltage drift issue. We also design and implement a passive balance board at exactly 2.7v with the same result.

• Gen2 Prius:
  The Gen2 Prius has been running on the LTO pack since then. As of today (12/19/2024), there have been no reported issues. However, drivers (one in Arizona and another in Brea, CA) have not observed any noticeable benefits, such as improved MPG. In some cases, the vehicle exhibits sluggish behavior during slow-speed cruising.
  
  
• Gen3 Prius:
  The Gen3 Prius, equipped with a larger 10Ah LTO pack, faced challenges despite the higher capacity. The sharp discharge curve occasionally triggered an error code, particularly in slow-moving traffic. We observed a similar issue with our LiFePO4 variant during extremely cold mornings. Installing a "soother" device to smooth out the charge/discharge curve improved the situation. However, the Uber driver using this vehicle reported no tangible benefits from the LTO upgrade. Additionally, the taller size of the 10Ah LTO pack made the trunk space unusable, which was a significant drawback as it limited luggage storage for passengers. As a result, the driver upgraded to the V3 sodium-ion battery on July 11, 2024 and never want to go back to LTO.

Conclusion:
While the long cycle life of LTO batteries is a clear advantage, the sharp charge/discharge curve poses a major issue, often triggering error codes in specific situations (e.g., extreme cold and low state of charge). This makes LTO an impractical choice for a consumer-ready solution.

Additionally, the high price of LTO cells further reduces their viability for large-scale or cost-sensitive projects. These challenges are among the reasons NexPower has moved away from LiFePO4 chemistry in favor of more suitable alternatives - Sodium-ion chemistry.

I hope this information helps anyone considering LTO batteries for their project.


Jack C.
Dr. Prius App

 

yep, I believe salt battery with affordable price tag and great durability is the way to go, many expensive lesson learnt to get us this far !!!