Lithium cobalt oxide, lithium iron phosphate, sodium ion, and quasi-solid state. We compared all four types of mobile batteries! Which is best for outdoor use?

Do you use your regular mobile battery outdoors without thinking about it?

Lithium-ion battery fires and explosions have become a common occurrence recently. In fact, according to a survey by the National Institute of Technology and Evaluation (NITE), 492 cases of lithium-ion battery fires were reported to NITE in 2024 alone. This is an increase of 77 cases from the previous year, the highest number ever.

In the past five years up to 2024, 1,860 accidents have been reported, and about 85% of these have resulted in fires, making them a very dangerous battery. Many of these accidents are said to be related to "lithium cobalt oxide batteries."

The reason why most of the accidents are caused by "lithium cobalt oxide batteries" is because they boast an overwhelming market share. Generally, when people talk about lithium ion batteries, they are referring to "lithium cobalt oxide (LCO)."

Furthermore, this "lithium cobalt oxide battery" is said to have lower thermal stability and a relatively higher risk of accidents than other battery chemistries currently used in mobile batteries, etc. However, have you ever taken your regular battery with you on a midsummer camping trip or midwinter snow activity without realizing it?

Why regular "lithium cobalt oxide (LCO)" increases the risk of accidents

Many accidents involving ordinary lithium-ion batteries (also known as "lithium cobalt oxide batteries") are believed to be caused by using them outside their operating temperature range. If you check the instruction manual, you will often find that the operating temperature range is between 0 and 40°C.

If you leave your battery in direct sunlight or in a closed car while camping in the middle of summer, it will easily exceed this operating temperature range. Conversely, even in the middle of winter, when temperatures drop below 0°C, regular lithium-ion batteries can still cause accidents, so caution is required.

High-temperature environments (generally above 45°C) are believed to accelerate internal reactions, increasing the risk of fire in the worst case scenario. It's generally believed that temperatures above 45°C make the flammable electrolyte in lithium-ion cobalt oxide batteries more likely to volatilize. This increases the battery's internal pressure and resistance, triggering the SEI film to begin decomposing, further increasing pressure and temperature. Eventually, the lithium cobalt oxide used in the positive electrode material begins to thermally decompose, releasing oxygen that reacts with the flammable electrolyte and gases, potentially leading to fire in the worst case scenario.

It is important to note that even at low temperatures, short circuits that can lead to fires can occur. At low temperatures, such as below freezing, metallic lithium is more likely to precipitate on the surface of the negative electrode. If these grow into needle-like structures (dendrites) and break through the separator, an internal short circuit occurs. An internal short circuit generates a large current locally, causing the temperature inside the battery to rise rapidly. This can cause a reaction similar to that at high temperatures, and in the worst case scenario, can lead to fire.

In other words, it is important to understand that using a lithium-ion battery outside of its operating temperature range increases the risk of fire and other accidents. If you are using a lithium-ion mobile battery outdoors, we recommend that you be aware of this point.

Alternatives to the flame-resistant "lithium-ion cobalt oxide battery"

There are five types of batteries currently available for mobile batteries: lithium cobalt oxide, ternary lithium, lithium iron phosphate, sodium ion, and quasi-solid state.

However, as we have already explained, "lithium cobalt oxide" is highly flammable. Next, "ternary lithium" is famous for being used in Tesla's electric vehicles (EVs). However, without a cooling system, it is said to be as flammable as "lithium cobalt oxide," and is rarely used in small devices where it is difficult to equip a cooling system.

As a result, lithium iron phosphate, sodium ion, and quasi-solid state batteries are realistic candidates for mobile batteries that are relatively easy to reduce the risk of accidents. We will also explain why these batteries are less likely to burn.

"Lithium iron phosphate" has a proven track record and is highly regarded for its safety

The reason why lithium iron phosphate batteries are less flammable is very simple. It's because they use highly stable lithium iron phosphate for the positive electrode. Lithium iron phosphate is thermally and chemically stable, with a higher decomposition temperature of over 500°C compared to lithium cobalt oxide, which decomposes at around 200°C. Even if decomposition does occur, it releases almost no oxygen, so it won't ignite even in the event of a short circuit. It is said to be less likely to explode.

It is also widely used by BYD, which currently boasts a production volume of EVs exceeding that of Tesla, and for outdoor enthusiasts, it has a proven track record of being used in many portable power sources that are even larger than mobile batteries, which is reassuring when assessing risk.

"Sodium ion" that does not use lithium

Sodium-ion batteries do not use lithium-based positive electrodes, but instead use sodium. And just like lithium iron phosphate, they release almost no oxygen even when thermally decomposed, so the risk of fire from reacting with the evaporated electrolyte is relatively low. Furthermore, while currently used electrolytes are flammable, sodium-ion batteries can use electrolytes that are more stable than lithium batteries, which has the advantage of making it less likely for the electrolyte and positive electrode to decompose and ignite or explode.

However, at present, the only commercially available mobile battery is ELECOM's DE-C55L-9000 series, which the manufacturer claims is the world's first and only sodium-ion battery mobile battery, so it can be said that it has a poor track record.

Quasi-solid-state batteries are a technology that has emerged in recent years.

Quasi-solid-state batteries are considered an intermediate technology that will act as a bridge to fully solid-state batteries, which are considered the most promising next-generation batteries. By turning liquid electrolytes into gels or highly viscous quasi-solids, the risks of leakage, evaporation, and fire are reduced, and the growth of lithium dendrites, which can be a problem at low temperatures, is also suppressed, reducing the risk of short circuits.

It is said to be an intermediate technology to fully solid-state batteries, and is expected to have advantages in terms of safety at both high and low temperatures. However, at present, its disadvantages are that it is less safe than fully solid-state batteries and is more expensive.

In recent years, it has become available commercially as a mobile battery, but there are still concerns about its safety record.

We obtained and thoroughly compared "lithium cobalt oxide," "lithium iron phosphate," "sodium ion," and "quasi-solid" materials.

As for "lithium cobalt oxide," most mobile batteries currently on the market are "lithium cobalt oxide," so I decided to purchase a mobile battery from a 100 yen store, which is reasonably priced and seems to be widely available.

It's extremely affordable at 1,100 yen (tax included) for 10,000mAh. It measures approximately 136 x 69 x 16mm and weighs approximately 219g, making it cheap, light, and powerful. It's no wonder that "lithium cobalt oxide" mobile batteries are the most popular.

By the way, the price per 1,000mAh is 110 yen, the volume is about 15,014㎣, and the weight is about 22g. There are many different types of mobile batteries, but if we use this as a standard and compare it with "lithium iron phosphate," "sodium ion," and "quasi-solid state," we may see some interesting results.

The "lithium iron phosphate" battery I purchased was the Green House "Mobile Battery 20000mAh Iron Phosphate GH-LFMBPA200 Series." It measures approximately 140 x 69 x 29mm, weighs approximately 375g, and costs 7,180 yen. The operating temperature range is 0 to 40°C.

ELECOM's DE-C55L-9000 series sodium-ion mobile battery is said to be the only commercially available "sodium-ion" mobile battery in the world at present. The battery has a capacity of 9,000mAh, measures approximately 106 x 87 x 31mm, weighs approximately 350g, and costs 9,980 yen (tax included). The operating temperature range is -35 to 50°C when discharging and 0 to 40°C when charging.

The "quasi-solid-state" mobile battery is the "SSPB (quasi-solid-state battery mobile battery) 10,000mAh" from HAMAKEN WORKS. It measures approximately 112 x 68 x 17mm, weighs approximately 195g, and costs 8,980 yen (tax included). The operating temperature range is -20 to 80°C.

[Comparison 1] Price, volume, and weight: Comparing per 1,000mAh

Since the capacities vary, it can be difficult to know how much each one costs or what its energy density is, so we've summarized the prices per 1,000mAh.

Price, volume, and weight comparison per 1,000mAh

Item name	Price per 1,000mAh	Volume per 1,000mAh	Weight per 1,000mAh
100 yen lithium cobalt oxide	Approximately 110 yen	Approximately 15,014㎣	Approximately 22g
lithium iron phosphate	Approximately 359 yen	Approximately 14,007㎣	Approximately 19g
sodium ions	Approximately 1,109 yen	Approximately 31,764㎣	Approximately 39g
semi-solid	Approximately 898 yen	12,947㎣	Approximately 20g

The results are as shown above. If you ignore cost performance, considering the wide operating temperature range and the amount of energy per weight and volume, "quasi-solid" is overwhelmingly the best. However, if you can ignore price, size, and weight, the strength of "sodium ions" at low temperatures is attractive.

[Comparison 2] Battery life: How many times can it be charged and discharged? Cycle life should also be considered.

The "lithium cobalt oxide" mobile battery is exceptionally cheap, partly because I bought it at a 100 yen shop. However, this does not take into account the cycle life, or how many times it can be charged and discharged. In fact, this cycle life is also published for each product, as shown below. I have also listed the product life assuming it is charged and discharged once a day.

Cycle life, cost per use, and product life of each type

Item name	Cycle Life	Cost per use	product lifespan
100 yen lithium cobalt oxide	Approximately 500 times	Approximately 2.2 yen	Approximately 1.4 years
lithium iron phosphate	Approximately 2,000 times	Approximately 3.6 yen	Approximately 5.5 years
sodium ions	Approximately 5,000 times	Approximately 2.0 yen	Approximately 13.7 years
semi-solid	Approximately 2,000 times	Approximately 4.5 yen	Approximately 5.5 years

In terms of cycle life and product lifespan, sodium-ion mobile batteries are actually excellent products and are also environmentally friendly. In this comparison, only the lithium iron phosphate mobile battery has a capacity of 20,000mAh, so it is at a slight disadvantage in this calculation, but it also turns out to be very cost-effective.

[Comparison 3] Operating temperature range: Should you use it according to the season? Or should you go for a "quasi-solid-state" battery?

I believe there are three ways to use a mobile battery safely and cost-effectively outdoors. The first is to use lithium cobalt oxide, which is the most widely used, affordable, lightweight, and small battery, while maintaining an operating temperature range of 0 to 40°C. This is a solid method.

Comparison of general operating temperature ranges

Item name	Typical Operating Temperature Range
100 yen lithium cobalt oxide	0〜40℃
lithium iron phosphate	0 to 40°C (lower risk of fire or explosion compared to lithium cobalt oxide, but charging performance is likely to decrease at low temperatures)
sodium ions	Discharging: -35~50℃, Charging: 0~40℃
semi-solid	−20〜80℃

However, many people find it impossible to maintain a temperature of 0-40°C outdoors in midsummer or midwinter. As a resident of Hokkaido, I find winter to be harsh even when not outdoors, and considering the inside of a car, maintaining a temperature of 40°C in summer is quite difficult.

So, the easiest solution at present is a "quasi-solid-state battery." HAMAKEN WORKS' "SSPB (quasi-solid-state battery mobile battery) 10,000mAh" has an operating temperature range of -20 to 80°C, which means you can use it in almost any location without any worries.

The only problem is the price: 8,980 yen (tax included). However, since the cycle life is about 2,000 times, it's not unrealistically expensive when you consider the running costs. It's a recommended option for those who only need one mobile battery.

However, few people believe that a single mobile battery can handle everything. This means that you have to choose different batteries for different seasons. For winter outdoor activities, sodium ion batteries are the best. Their operating temperature range is -35 to 50°C when discharging and 0 to 40°C when charging. As long as you pay attention to the temperature when charging, they are more tolerant of low temperatures than quasi-solid-state batteries.

On the other hand, to combat the summer heat, I have already started actively using lithium iron phosphate batteries. Most of them have an operating temperature range of 0 to 40°C, the same as regular lithium-ion mobile batteries, but all of them claim to reduce the risk of fire or explosion.

Due to the crystalline structure of the lithium iron phosphate used in the positive electrode, it is considered to have relatively low risk compared to lithium cobalt oxide, and is widely used in portable power sources for EVs and camping, so it can be said that it has a proven track record and is therefore very reliable.

However, lithium iron phosphate has the characteristic that its charging performance is easily reduced at low temperatures, especially below 0°C, so I try to use sodium ion batteries in extremely cold places in winter and lithium iron phosphate batteries in the summer sun to prevent accidents caused by careless use.

If we're not careful, temperatures above 40°C can even rise in the home, so we use lithium iron phosphate mobile batteries for our young sons. Prices have recently come down, so a good balance between safety and cost is also an important point.

The basic temperature range for a mobile battery is 0 to 40°C! If it goes above that, carefully consider the temperature.

Mobile batteries have become popular along with smartphones, but the basic operating temperature range is 0 to 40°C. This is also true outdoors, so it is even more important to be careful to use them within this temperature range.

Some people may be careful about high temperatures due to the high number of accidents that occur in the summer, but in fact, there is a risk of fire or explosion even at low temperatures, so caution is required even in winter outdoor fields.If you are using a mobile battery in an area where it is absolutely impossible to maintain the operating temperature range, we recommend using a mobile battery with the appropriate performance and characteristics, such as lithium iron phosphate, sodium ion, or quasi-solid state, depending on the environment you intend to use it in.

*The values ​​and characteristics in this article are based on the nominal values ​​of each manufacturer and general knowledge. Actual behavior may vary depending on individual differences and environmental conditions. Please follow the temperature ranges in the instruction manual when charging and discharging.

Mobile battery comparison summary [by type]

Item name	Strong Points	Cons
Lithium cobalt oxide	High energy density High cost performance	There is a risk of fire at high and low temperatures
ternary lithium	Achieves both high output and high energy density	There are almost no mobile batteries available on the market at the moment.
lithium iron phosphate	Low risk of fire Relatively good cost performance	Low energy density Charging performance tends to decrease at low temperatures
sodium ions	Low risk of fire Excellent low-temperature performance Long cycle life	Low energy density High initial costs
semi-solid	Low risk of fire High temperature resistance Little performance degradation even at low temperatures	Prices are high Few commercially available products

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Saito Titoce

Former monthly camera magazine editor. While pursuing the spectacular views of Hokkaido and the wildlife, I was completely hooked on the outdoor life of camper vans and sleeping in my car. While traveling the entire country with his 2-year-old son and wife, he is a photographer writer who photographs and writes everything he has experienced, not only cameras and lenses, but also outdoor camping, child-rearing, PC gadgets, cooking, and dieting. OUTDOOR GEARZINE plans to write a variety of articles, focusing on the QOCL (Quality of Camping Life) Improvement Committee, which will improve the quality of life in camping and camper vans.

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