Development and Characteristics of Small Lithium-Ion Secondary Batteries
NICHICON CORPORATIONIn recent years, the provision of new products and services utilizing IoT, artificial
intelligence and cloud platforms has been on the rise amid the expansion of environmental
power generation (energy harvesting) systems that convert light, heat, vibration and radio
waves into electricity. Furthermore, the advance of autonomous vehicles that run without
drivers Advanced Driver Assistance Systems (ADAS) and other car electronics are creating
greater demand for storage batteries.
There is a demand for products that have the ability to charge/discharge with large currents
over longer periods of time. Electric double layer capacitors have high power density but
low energy density while typical lithium-ion secondary batteries have high energy density
but low power density. The Toshiba Infrastructure Systems & Solutions Corporation(hereinafter, “Toshiba”) SCiBTM secondary batteries meet these demands with a technologythat addresses the weaknesses of lithium-ion batteries, which include safety, cycle
durability, low-temperature usage and high-speed charge-discharge performance.
NICHICON licensed this technology from Toshiba and developed small lithium-ion
secondary batteries that are especially small in size, enable repeated charge/discharge

Power density: W/kg-1

performance and offer both power and energy density.

Energy density: Wh/kg-1

Diagram 1: plot for storage batteriesThis product utilizes lithium titanate (LTO) for the negative electrodes, possessing highrate* (20C maximum) rapid charge/discharge performance similar to electric double layer
capacitors. It is also durable, capable of over 18,000 charges/discharges at a rate of 10Cand low temperature characteristics enabling operation at temperatures reaching -30°C.
Furthermore, it is a safe small lithium ion secondary battery with extremely low risk ofignition or smoking due to less lithium metal deposition, which causes deterioration andshort circuits.
Structure and Characteristics
In general, the structure of lithium ion secondary batteries is roughly divided into cylindrical,
square and button shapes. The small lithium-ion secondary batteries developed byNICHICON are cylindrical, based on the same general structure as our basic electricdouble layer capacitor and consist of positive and negative electrodes, a separator,
electrolytic solution and exterior housing materials.
The positive and negative electrodes are each coated with a thin metal foil layer. LTO, themain material used for the negative electrode, is non-combustible and more thermallystable than carbon-based materials used in many lithium-ion secondary batteries. With theLTO negative electrode specification, there is no reaction with electrolytic solution even at
higher temperatures. This reduces the possibility of a reaction between the negativeelectrode material and the electrolytic solution from triggering thermal runaway. Whenreleasing lithium ions, LTO has the property of changing into a state near that of insulation,and even if a partial short circuit occurs, it does not spread to the entire battery. The LTO
surface where the short circuit occurs is insulated, suppressing the advance of thedischarge reaction. For this reason, even if an internal short circuit does occur, the battery’s
exothermic reaction is dramatically reduced.
Cycle Characteristics
The current rate of charging/discharging a batteries capacity in one hour is defined as 1C.
The retention rate of lithium-ion secondary batteries is about 80% at a 1C rate. The smalllithium-ion secondary batteries developed by NICHICON maintained a capacity of 85%
during 18,000 charge/discharge cycle tests conducted at 10C (charge/discharge in 1/10 ofan hour), ten times the rate of typical lithium-ion secondary batteries, making this a device
offering excellent cycle life at a high rate (18,000 cycles are equivalent to charging thebattery five times a day for about 10 years).

120容量維持率/ %Capacity retention rate/%

10080

一般的なリチウムイオン電池の場合
When
using general lithium ion batteries

Lifespan 数百～数千サイクルで寿命with hundreds to thousands of cycles

60

Even大電流サイクルで25,000回充放電しても、
when charging and discharging 25,000 times
in a large
current cycle, the discharge capacity (1C)
放電容量（1C）は初期の80%以上を維持。
is maintained during the initial 80% of operation or longer.

40・Charge
and discharge25deg.C
cycle conditions:dec.C CCCV
10 C SOC 1-100% CCCV・充放電サイクル条件;
10C SOC 250-100%・1C容量算出用充放電条件
・1Ccharge/discharge conditions for capacity calculation
充電条件;
25deg.C
1C 2.8V30min
Chargecondition:25 dec.C
1 CCCCV
2.8 V30min
CCCVrest
30 minrest 30 min
放電条件; 25deg.C 1C 1.8V
Discharge condition: 25 deg. C 1 C 1.8 V

2000

5,000

10,00015,00020,00025,000サイクル回数
Numberof cycles

Diagram 2: Charge/discharge cycle characteristics

Rate Characteristics
This product can support high-speed charge/discharge of up to 20C. When charging at
20C, an approximately 80% high-speed charge is possible in three minutes, which isoptimal for short-time charging applications. In addition, when discharging at 20C,approximately 95% of charge capacity can be discharged in three minutes, making thisdevice optimal for applications requiring high power. The rate characteristics of this productCharging rate (%)

are shown in diagrams 3a and 3b.

Super-fast charging to 80% of
total capacity in three minutes

Charging time (minutes)

Diagram 3a: Charge characteristics

Residual rate (%)

Super-fast discharge possible inthree minutes

Discharge time (minutes)

Diagram 3b: Discharge characteristics

Low Temperature Characteristics
Excellent low-temperature characteristics enable charge/discharge even in low-temperatureenvironments of -30°C. Since there is no lithium deposition on the LTO negative electrode itis safe to use even in low temperature environments, and even when repeatedly charged
and discharged, there is no deterioration in capacity or other damage to the batteries

Discharge capacity change rate (%)

performance, offering excellent durability in low-temperature environments.

Can be used
at low-temperatures of -30°C

Temperature (°C)

Diagram 4: Low-temperature characteristics

Safety
As seen in Table 1, NICHICON conducted safety testing on our small lithium-ion secondary
batteries and confirmed that there were no explosions or fire. LTO negative electrodes havepotential of 1.5 V or higher in the SOC range (0–100%) and in principle, lithium deposition
does not occur. Even in the overcharge region, it was confirmed that LTO negativeelectrodes ensure a potential of approximately 0.5 V or higher and lithium deposition does
not occur. Thus, one feature of this product is that even when overcharged, there is nomechanism for causing an explosion or fire.

Test item

Test detailResultCrushing

After full charge, inserted semi-circular indenter (φNo explosion or10 mm) so that longitudinal axis of cylindrical battery

fire

was perpendicular to the indenter and crushed to
50% of pre-test size.
Nail piercing

After full charge, pierced with 3 mm diameter nailNo explosion or

inserted vertically in center of battery at a speed offire

5.5 mm/sec without removal.
Blunt Nail test

Using Blue Nail as a fully charged battery,

No explosion orpressurized battery at a speed of 0.1 mm/second.

fire

When battery power dropped by 0.5 V or more, it
was deemed to be a short circuit and nail descent
was stopped.
External short

Positive and negative electrodes of battery

No explosion orcircuit

connected to an external resistor of about 1 m Ω

fireand short-circuited.
Overcharge

Using a power source that can be used at 10 V or

No explosion or

higher, the battery is energized from the discharge

firestate to 1C (or 2 to 10 C) of the rated capacity up to250% of the rated capacity.
ForcedFrom the discharge state (SOC 0%), reverse charge

No explosion ordischarge

the battery at 1 C for 90 minutes.

fireTable 1: Safety test results

Future Expectations
To realize an IoT society connected by all kinds of networks, all kinds of devices will require
power supplies, but there are some places where power supply wiring and changing
batteries is difficult. For this reason, energy harvesting technologies that convert light, heat,vibration and radio waves into electricity and secondary batteries capable of frequent,repeated storage and discharge cycles are desirable.
For example, utilizing the characteristics of the small lithium-ion secondary batteries incombination with power supply IC, it is possible to drive environmental sensors for a longtime and monitor data on temperature, humidity and illuminance. Also, utilizing high ratecharacteristics compatible to a maximum of 20C, high-speed charging in a short time ispossible in combination with a step-up/step-down charge IC.
Additionally, we discovered the potential for approximately 100C in short-time intermittent
pulse discharging and expect to further expand applications combining long-term cycle
characteristics with high-speed charge/discharge characteristics. Combined with its safetycharacteristics, we anticipate this product will advance applications such as wearables andother familiar devices.
Note *: High-rate high-speed charge/discharge performance:
The current rate when charging/discharging battery capacity in one hour is defined as 1C.
The ability to charge/discharge at a rate higher than 1C is referred to as high-rate highspeed charge/discharge performance.
Further reading* 1: New type of secondary battery SCiB offering excellent safety: Kosugi, Inagaki, Takami* 2: New type of secondary battery SCiB for hybrid vehicles offering excellent durability andsafety: Takami, Kosugi, Honda* 3: New type of rechargeable battery SCiB battery pack for HEV: Kosugi, Takami, Honda* 4: IoT power supply–battery problems: Keiji Takeuchi