How smartphone batteries have evolved

We often criticize modern smartphones for their short operating time. Now they live a day, a maximum of two - but 20

years ago, mobile phones lasted up to a week of active use.

Such a comparison is unfair, because newsmartphones are much more advanced than the Nokia 3310 and consume an order of magnitude more energy. The fact that modern batteries provide them with a day or two of battery life is the result of decades of scientific research and experimentation.

Recent developments give hope thatfuture smartphones will offer significantly longer battery life. But when will this happen? We tell you how power sources have evolved and what innovations will make it possible to make a breakthrough in the autonomy of smartphones.

The device and principle of operation of the battery

Any source of electrical current worksin a similar way. It is based on two electrodes in contact with an electrolyte - a substance capable of conducting an electric charge due to a high concentration of ions (positively charged cations and negatively charged anions). As an electrolyte, solutions of alkalis, acids or salts act.

Negatively charged anode (lead, cadmium,zinc and other metals) contains a reducing agent that donates electrons during an oxidative reaction. These electrons pass through the external circuit to a positively charged cathode (lead oxide, manganese oxide, and others). There they participate in the reduction reaction of the oxidizing agent.

When connected to the load electrodes, aa closed electrical circuit through which a discharge current flows. It is formed by the movement of electrons in metal parts and anions with cations in the electrolyte.

Batteries in the first mobile devices

The world's first cell phone Motorola DynaTACThe 8000X was released in 1983 and was powered by a nickel-cadmium (Ni-Cd) battery. Cadmium hydroxide was the anode and nickel hydroxide was the cathode. An alkaline solution was used as the electrolyte.

The charging time of such batteries reached sixhours, while they provided only about an hour of battery life. Also, Ni-Cd batteries were subject to the memory effect - a decrease in capacity as a result of recharging an incompletely discharged power source. Because of this, I had to completely discharge and charge them. Otherwise, the operating time did not even reach one hour, and the battery itself quickly failed.

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When connecting the Ni-Cd load, the batteries quickly heated up. In addition, they were large and heavy, which became a problem as cell phones got smaller.

Nickel-metal hydride (Ni-MH) batteries were designed to eliminate these shortcomings. Instead of cadmium hydroxide, the role of the anode is performed by a nickel-lanthanum or nickel-lithium metal hydride alloy.

Compared to Ni-Cd, a new type of batteryoffered much higher power and energy density. The last point made it possible to reduce the size of Ni-Mh batteries, while increasing the capacity.

Such a set of characteristics did Ni-Mhattractive solution for cell phones. However, there were also disadvantages: such batteries were still very hot and often “swollen”. They were also subject to the memory effect. However, they were popular until the early 2000s, when a new technology appeared on the horizon.

Transition to Li-ion

The lithium-ion battery patent wasregistered by the American scientist Manly Whittingham in 1970. It proposed the use of a graphite anode and a lithium oxide cathode. A porous separator was located between them, which allowed lithium ions to pass through and prevented the contact of the electrodes.

In 1985, the Japanese Akira Yoshino developedeffective electrodes for such batteries. A copper foil substrate was used for the anode, and aluminum foil for the cathode. The first serial Li-ion battery was released by Sony in 1991.

The transition to the new technology significantly increased the energy density, and also saved the batteries from the pronounced memory effect. Another plus was the reduction in charging time.

The first Li-ion batteries had energydensity 100 W*h/kg. Since then, there have been many technology optimizations, experiments with materials and layout - and today we have batteries with a density of 300 Wh / kg.

The shape of the batteries also changed to maximizeuse space efficiently. So, the iPhone 11 Pro Max, released in 2019, received an L-shaped battery with a capacity of 3969 mAh. For comparison, the iPhone XS Max used a battery of two cells, the total capacity of which was only 3174 mAh.

They also experiment with different materials.For example, instead of a graphite anode, silicon-oxygen anodes began to be used, capable of storing four times more lithium ions. The first smartphone with such a battery was Xiaomi 11 Ultra in 2021.

Today, 5000 mAh batteries are foundeven in inexpensive smartphones. So the development of Li-ion batteries continues. For example, the thickness of the separator, as well as the metal substrates of the anode and cathode, gradually decreases. All this makes the battery cells smaller while maintaining capacity.

There was an acute problem with the compaction of the layoutheating. Modern Li-ion batteries are 95% efficient. The remaining 5% of the energy is converted into heat. At first glance, this is not much - but with engineering errors, even such heating can damage the battery.

Another problem with Li-ion batteries isgradual degradation - in 2 years, a Li-ion battery loses an average of 10% of its capacity, even if it is not used. The average life of such batteries is 5 years, after which they need to be dispose of – and it is very difficult.

However, these parameters are much better than10 year old batteries. The price of Li-ion batteries has also fallen: if in 2010 1 kWh cost $1,183, today it costs only $130. And when compared with 1991, the price drop was 97% - then 1 kWh cost $ 3,000.

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What's next

One technology that could see the light of day in the coming years is lithium-sulfur batteries. Their design is similar to lithium-ion, but instead of graphite, sulfur is used in the cathode.

According to scientists, this discovery will allow creatingbatteries with an energy density of up to 400-500 watt-hours per kilogram of mass. This is about twice as high as modern lithium-ion batteries.

Now such batteries are not able to withstanda large number of reloads. Another problem on the way of their distribution is poor compatibility with existing electrolytes, which reduces power and energy density. However, this may change soon.

In 2021, Japanese scientists developed solid electrolyte for lithium-sulfur batteries.The first experiments showed a significant increase in energy density, but the new material quickly oxidized and lost its properties with each subsequent charging cycle.

This was corrected by adding nanoparticles of carbon atoms and various lithium salts to the electrolyte. As a result, the oxidation slowed down, which protected it from further destruction.

Further experiments led to an unexpected opening. Scientists at Drexel UniversityPhiladelphia accidentally created a form of γ-sulfur that is stable at room temperature. The cathode based on it has withstood thousands of charge-discharge cycles without a decrease in performance even after a year. While such developments are in the early stages of development, so we are unlikely to see their commercial implementation.

Another promising direction is batteries withsolid state electrolyte. They not only offer high capacity, but also eliminate one of the reasons for the degradation of Li-ion batteries - the deposition of lithium metal in tree-like structures (dendrites) from the anode to the cathode. They pierce the separator and can cause a short circuit.

In addition, the solid state electrolyte will makebatteries resistant to negative temperatures. Now Li-ion batteries work effectively in a rather narrow temperature range - from 0 ° C to + 35 ° C.

At low temperature, the viscosity of the liquidelectrolyte increases sharply, and the transport capacity of lithium ions becomes difficult. As a result, the battery drains quickly. The use of a solid state electrolyte will eliminate this problem.

Manufacturers are currently working onbatteries of this type. In March, Xiaomi introduced its first solid-state battery with a record energy density of 1000 Wh/L. For comparison, current Li-ion batteries have a capacity of 693 Wh / l. Perhaps the new development will find application in smartphones as early as 2024.

In 40 years, batteries in phones have come a long way from huge cells that charge in 6 hours and give out only an hour of operation, to thin batteries with a capacity of 5000 mAh, replenishing the charge in half an hour.

In the future, we may see smartphones living up toweeks, and before that you will have to remember to put them on charge at least once a day. However, for most this is not a problem, and fast charging technologies make life much easier.

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