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Development of a compact, large-capacity, highly safe laminated lithium-ion battery

Hard-flammability of batteries–using less-volatile electrolytes–with battery capacity of 130 Wh and energy density of 600 Wh/L was demonstrated

December 6, 2019

Hitachi, Ltd. today announced the development of a laminate-type lithium-ion battery*1 (hereafter referred to as "LIB") utilizing a less volatile electrolyte material. The LIB developed provides an energy density of 600 Wh/L while assuring a high level of safety. The resultant battery capacity is thus 130 Wh, while the size of the LIB is 60% less than that of our previous model. The developed laminate-type LIB was tested on the basis of safety standard IEC62660 (by, for example, crush tests*2 and overcharge tests*3), and the test results demonstrated that it would not ignite under such abnormal conditions. This battery technology makes it possible to (i) effectively utilize the interior space of a car equipped with LIBs and (ii) install power sources for adjusting the demand/supply balance of renewable energy in a small space.


Figure 1: Conventional laminated LIB (left) and developed LIB (130 Wh) (right)

Background and issues

  • It is necessary to provide LIBs that can be used safely, have a large capacity, and are compact enough for battery systems that can be used widely in a variety of situations in daily life.
  • An issue of organic solvent electrolytes is its volatilization temperature and flash point which can be as low as around room temperature. Installing parts to reinforce and cool the battery system to ensure the safety of LIBs results in a tradeoff with compactness.

Developed technology

  • Less volatile electrolyte for high safety LIB
  • Development of a compact structure with no surplus space
  • Electrode structure assuring both high safety and high energy density

Verified effect

A laminated LIB with battery capacity of 130 Wh, energy density of 600 Wh/L, and 60% smaller size than a conventional LIB [see Figs. 1(a) and (b)] was developed, and a safety-standard test based on IEC62660 revealed that the developed LIB does not ignite under abnormal operations.

Papers presented, academic societies, events, etc.

A part of the results from this work were announced at the 236th Electrochemical Society Meeting (in Atlanta, USA from October 13, 2019) and the 3rd International Advanced Automotive Battery Conference (in Chiba, Japan from October 28, 2019).

Details of developed technology

1. Development of non-volatile electrolyte for ensuring high safety of LIB

In conventional laminated LIB utilizing organic electrolytes, if the volatility of the electrolyte is high, this can lead to an increase in internal pressure which may cause the LIB to burst and electrolytes to leak, increasing the risk of poisoning and ignition. By improving a non-volatile electrolyte*4 (developed in collaborative research with Tohoku University) by utilizing simulation-analysis technology and devising a composition that achieves both low volatility and good charge and discharge reaction, Hitachi has achieved a volatilization temperature*5 higher than 100℃ and suppressed volume expansion (during a simulating test of battery expansion*6) during heating.

2. Development of compact structure with no excess space

A conventional LIB (Fig. 2(a)) has a laminated sealing part around its outer periphery for maintaining airtightness. However, this part represents surplus space that is not involved in power storage, and that surplus space is a factor in lowering energy density. By adopting the non-volatile electrolyte described in Section 1, the rise in internal pressure can be suppressed, and the laminated bonding part can be simplified. This improved configuration made it possible to configure the LIB structure with high energy density (Fig. 2 (b)).


Fig. 2: Schematic diagram of battery structures: (a) conventional LIB and (b) developed LIB

3. Electrode structure combining high safety and high energy density

Aiming to enhancing energy density, we investigated thinning of the electrolyte layer that provides insulation between the positive and negative electrodes. Excessive thinning of the electrolyte increases the probability of heat generation due to a short circuit between the electrodes, which may cause ignition and lead to decreased safety. We therefore modeled the mechanism of heat generation and ignition, calculated the optimum thickness of the electrolyte layer, and devised a battery design that increases energy density while ensuring high safety level.

As a result of the above-described structure, the developed LIB’s energy density is 600 Wh/L, namely, 50% higher than our previous model, and its size is 60% smaller. The developed LIB was tested in accordance with safety standard IEC 62660, and the safety test demonstrated that it does not ignite under abnormal conditions. We expect this LIB technology to reduce the number of components (such as reinforcing materials and cooling mechanisms) required to ensure the safety demanded of LIB systems using organic electrolytes, and that reduction will make battery systems more compact and improve their price competitiveness.

Part of this development was carried out as part of a contracted project called “Innovative Science and Technology Initiative for Security” of the Acquisition, Technology & Logistics Agency (ATLA).

*1
Laminated LIB: A lithium-ion battery composed of a laminated positive electrode, negative electrode, and electrolyte, which is covered with aluminum-laminate sheet and sealed by heat fusion
*2
A battery-safety test simulating a short circuit caused by battery deformation
*3
A battery-safety test simulating a short circuit caused by precipitation of lithium dendrite
*4
February 16, 2018 News Release
Succeeded in trial production of a highly safe lithium-ion rechargeable battery utilizing a new non-flammable electrolyte
https://www.hitachi.com/New/cnews/month/2018/02/180216.html
*5
Volatilization temperature: Temperature at which the weight of liquid components decreases by 2% according to thermogravimetric differential thermal analysis (TG-DTA)
*6
A test in which a battery element containing an electrolyte is sealed with an exterior material and heated at 100℃.

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