Small Li-Ion Rechargeable Battery Optimized for the IoT Market
NICHICON CORPORATIONIn recent years, the internet of things (IoT) has been radically transforming people’s lives.
A variety of products embedded with an array of sensors transmitting data are becoming
indispensable for efficiently analyzing data using AI, advancing all kinds of technologies
and providing notifications when an abnormality has occurred. These sensors require apower supply to operate, resulting in a demand for new storage battery devices.
Examples of solutions using IoT are as follows. (Image 1)
1. Smart homes
IoT sensors are installed in homes collecting information such as the temperature andhumidity of each room. By analyzing the distribution of temperature and humidity, airconditioning can be directed where needed to humidify or dehumidify the air, creating a
comfortable living space for the occupants.
2. Disaster detection
The installation of IoT sensors in houses, buildings and near mountains and rivers enables
the rapid warning of dangers using voice guidance and lights when a fire, flood or
earthquake occurs. People can receive information quickly and evacuate, keeping damage
to a minimum.
3. Smart factories
The installation of IoT sensors on factory lines or in warehouses enables the real time
monitoring of production line operating status and inventories. This information enables
production quantity adjustments and production line abnormality detection.
4. Smart agriculture
Installing IoT sensors in greenhouses to collect and analyze data on temperature humidity
and light to create an optimal environment for plant growth.

Image 1: Solutions using IoTSensors can operate anywhere when using a commercial power supply. However, in cases
where a power supply is unavailable, storage devices are required. In many cases, aprimary battery is used, but primary batteries have a short service life and must be replaced
periodically. Switching to a rechargeable battery mounted together with an energy
harvester enables the system to become self-sustaining and maintenance-free, This results
in an increased demand for rechargeable batteries optimized for IoT sensor applications.
One example is the environmental sensor being considered in collaboration with RICOH
Electronic Devices Co., Ltd. (Image 2) Electricity generated by a solar panel is stepped
down using a low energy consumption electric current step-down DC-DC converter for
RICOH Electronic Devices’ energy harvester and stored in a small lithium ion rechargeable
battery. By stepping down the stored energy with a low energy consumption electric current
step-down DC-DC converter and driving sensors and a wireless module that can measuretemperature, humidity, pressure and light, this information can be transmitted via Bluetoothfor data collection. It is also equipped with an IC that monitors battery voltage, making it
easy to know how much battery energy remains. Environmental sensors equipped with ourSLB Series 0.35 mAh (φ 3 × 7 L mm) of small lithium ion rechargeable batteries canachieve maintenance- free operation when combined with solar power generation. The SLB
Series is optimal for this application because it is capable of low current charging and highcurrent discharge excellent cycle characteristics and a long service life. The internal
resistance of the SLB series is lower than ordinary lithium ion rechargeable batteries
allowing it to be charged using a small current. Energy harvesters generate small charging
currents giving the SLB series an advantage compared with other batteries. The lower
internal resistance allows for more energy to be discharged in a shorter amount of time IoT
data is collected using various communication methods and the amount of power required
differs depending on the amount of information and distance. This will result in increased

power consumption and a larger current is required. In order to discharge with a large
current, we would need to increase the product capacity, which increases the size and cost.
The SLB Series can generate a large current avoiding the need to make the product bigger
and more costly. The SLB series can be charged and discharged Thousands of times morecompared with ordinary lithium ion rechargeable batteries, contributing to maintenance-freeoperation.

Image 2: Environmental sensor (collaboration with RICOH Electronic Devices)
The SLB Series structure and features are shown below. The basic technology is based onToshiba Infrastructure Systems & Solutions Corporation rechargeable battery SCiB
technology, with the added features described below. By adopting lithium titanate (LTO) for
the negative electrode, the developed products have a high of rapid charge/discharge rate*(maximum 20C). They have a high input/output density that approaches electric double
layer capacitors. It is also durable, capable of 25,000 charge/discharge cycles at a rate of

10C and low temperature characteristics enabling operation at -30°C. This safe, smallsized lithium ion rechargeable battery inhibits the transfer of lithium metal between theelectrodes, which is a cause of short-circuiting and deterioration, with an extremely low
danger of ignition smoke.
Structures and features
In general, the structure of lithium ion rechargeable batteries is roughly divided intocylindrical, square and button shapes. The SLB series developed by NICHICON iscylindrical, based on the same basic structure as our electric double layer capacitor,
consisting of positive electrodes, negative electrodes, separators, electrolytic solution andexterior materials.
The positive electrode and the negative electrode are thin metal foil coated with positiveelectrode material and negative electrode material. The LTO, which is the main material
used for the negative electrodes, is more thermodynamic than the carbon material used inmany lithium ion rechargeable batteries. LTO is a stable noncombustible material. LTO
negative electrode does not react with the electrolytic solution even in the high temperature
range, this makes it unlikely for thermal runaway caused by the reaction between thenegative electrode and the electrolytic solution to occur. In conditions where lithium ions arereleased, the LTO has a property enabling it to change states from conductive to insulation,and even if a short-circuit reaction partially occurs, it does not spread to the entire battery
as the LTO surface at the short-circuited portion is insolated and the discharge reaction issuppressed. Thus, even if an internal short circuit occurs, the exothermic reaction of thebattery becomes lessened.
Cycle characteristics
The current rate when charging/discharging the batteries capacity in one hour is defined as1C. General lithium ion rechargeable battery cycle characteristics are said to be about 80%
of capacity retention rate at several hundred to several thousand cycles when charging anddischarging at a rate of 1C. However, the SLB Series maintains a capacity of 80% or moreeven when charging/discharging at a ten times higher rate of 10C (1/10th hour charging ordischarging) 25,000 times in a cycle test, making this a battery with excellent high-rate
cycle life (25,000 cycles corresponds to the number of charges/discharges conductedseven times a day for about 10 years).

容量維持率/ %Capacity retention rate/%

12010080

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 25
0-100%・1C容量算出用充放電条件
・1Ccharge/discharge conditions for capacity calculation
充電条件;
25deg.C
1C 2.8V
30min
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

Image 3: Charge and discharge cycle characteristics

Rate characteristics
The SLB series can handle rapid charging and discharging at a maximum rate of 20C.
When charging at 20C, a rapid charge to about 80% in three minutes is possible, enabling
quick charging. Also, when discharging at 20C, about 95% of the capacity is discharged inthree minutes, making it suited for applications requiring high power. The ratecharacteristics of the battery are shown in Images 4a and 4b.

Charging rate (%)

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

Charging time (minutes)

Residual rate (%)

【図 3ａ 充電特性】
Image 4a: Charging characteristics

Super-fast discharge possible inthree minutes

Discharge time (minutes)【図 3b 放電特性】
Image 4b: Discharge characteristics

Temperature characteristics
Charging and discharging are possible even in low temperature environments of -30°C.,
offering excellent low-temperature characteristics. Since lithium does not migrate from theLTO negative electrode in a low-temperature environment it is safe, and even when
repeatedly charged and discharged, battery performance deterioration, such as reduced

Discharge capacity change rate (%)

capacity, does not occur. Durability in low-temperature environments is also excellent.

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

Temperature (°C)
Image 5: Low-temperature characteristics

Safety
The safety tests in Table 1 were performed on the SLB Series and it was confirmed that norupturing or ignition occurred. The LTO negative electrode has a potential of 1.5 V or morein the state of charge (SOC) range (0 to 100%), and in principle, lithium precipitation does
not occur. Even in the overcharged range, the LTO negative electrode assures a potentialof about 0.5 V or more, and the test confirmed that lithium migration does not occur. In theunlikely event that overcharging occurs, there is no mechanism that will cause rupture orignition, which is one of the features of this product.

Test items

Test details

ResultCrushing

After a full charge, placed the vertical axis of the cylindrical battery

No rupture or ignition

vertically within the indenter having a radial indenter (φ10 mm) andcrushed it to 50% of pre-test condition.
Nail puncture

After a full charge, vertically pierced the center of the battery with a 3

No rupture or ignition

mm nail at a speed of 5.5 mm/sec and left it.
Blunt nail test

After a full charge, a blunt nail is pressed into the battery at a speed

No rupture or ignitionof 0.1 mm/sec. When battery voltage drops by 0.5 V or more, it isconsidered to be a short circuit and the ingress of the nail is stopped.
External shortcircuit
OverchargingConnected positive and negative terminals of the battery to an

No rupture or ignition

external resistor of about 1 m Ω and short-circuited it.
Using a power supply providing 10 V or higher, the battery is

No rupture or ignition

charged from a discharged state at 1C (or 2 to 10C) to 250% of therated capacity.
Forced discharge

From the discharged state (SOC 0%), the battery was reverse

No rupture or ignition

charged at 1C for 90 minutes.

Table 1: Safety testing results

Future expectations
The SLB Series of small lithium ion rechargeable batteries are a product applicable not onlyin the IoT market, but also in a variety of other fields. NICHICON will optimize the productfeatures in existing markets and new markets.
Note *: High-rate rapid 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.

References
1. New rechargeable battery SCiB offering excellent safety: Kosugi, Inagaki and Takami
2. New rechargeable battery SCiB for hybrid vehicle with excellent durability and safety:Takami, Kosugi and Honda
3. New rechargeable battery SCiB battery pack for HEV: Kosugi, Takami and Honda
4. IoT power supply—battery problems: Keiji Takeuchi