Recently we talked about the history of the invention of lithium-ion batteries, which gave a powerful impetus to the development of portable electronics. Every year, the tech media informs us about the upcoming energy revolution - just a little more, another year or two, and the world will see batteries with fantastic characteristics. As time goes on, but the revolution is not visible, our phones, laptops, quadcopters, electric cars and smartwatches still have various modifications of lithium-ion batteries. So where did all the innovative batteries go, and is there any alternative to Li-Ion at all?
When to expect the battery revolution?
Sorry to upset you, but it has already passed. It just stretched out for a couple of decades and therefore went almost unnoticed. The fact is that the invention of lithium-ion batteries was the apogee of the evolution of chemical batteries.
Chemical current sources are based on a redox reaction between elements. There are only 90 natural elements in the periodic table that can participate in such a reaction. So, lithium turned out to be a metal with the limiting characteristics: the lowest mass, the lowest electrode potential (–3.05 V) and the highest current load (3.83 Ah / g).
Lithium is the best cathode active substance on earth. The use of other elements can improve one performance and inevitably degrade another. That is why experiments with lithium batteries have been going on for 30 years already - by combining materials, among which lithium is invariably, researchers create types of batteries with the necessary characteristics that find very narrow application. The good old battery with a lithium-cobalt oxide cathode, which came to us already from the 80s of the last century, can still be considered the most widespread and universal due to the excellent combination of voltage, current load and energy density.
Therefore, when another startup through the mouth of the media loudly promises the world an energy revolution from day to day, scientists are modestly silent about the fact that the new batteries have some problems and limitations that have yet to be solved. They usually cannot be solved.
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The main problem with "revolutionary" batteries
Today, there are many types of batteries with different chemical compositions, including those without the use of lithium. Each type with its own characteristics has found its application in a certain type of technology. Lightweight, thin and high-voltage lithium-cobalt batteries have long been found in compact smartphones. Hardy, powerful, but very large lithium-titanate batteries fit into public transport. And low-capacity fire-safe lithium-phosphate cells are used in the form of large arrays in power plants.
Still, the most popular are lithium-cobalt batteries for consumer mobile technology. The main criteria they meet are a high voltage of 3.6 V while maintaining a high energy intensity per unit volume. Unfortunately, many alternative types of lithium batteries have a much lower voltage - below 3.0 V and even below 2.0 V - which cannot be powered by a modern smartphone.
It is possible to compensate for the subsidence of any of the characteristics by combining batteries into cells, but then the dimensions grow. So if another promising battery with miraculous characteristics turns out to be unsuitable for use in mobile technology or electric vehicles, its future is almost guaranteed a foregone conclusion. Why do you need a battery with a life of 100 thousand cycles and fast charging, from which you can only power a wristwatch with arrows?
Failed experiments
Not all of the batteries described below can be considered unsuccessful - some require a very long revision, some may find their application not in smartphones, but in specialized equipment. Nevertheless, all these developments were positioned as a replacement for lithium-ion batteries in smartphones.
In 2007, an American startup Leyden Energy received $ 4.5 million in investments from several venture capital funds to create what they themselves stated as a new generation of lithium-ion batteries. The company used a new electrolyte (Solvent-in-Salt) and a silicon cathode, which significantly increased energy intensity and resistance to high temperatures up to 300 ° C. Attempts to make laptop batteries out of the box ended in failure, so Leyden Energy reoriented itself to the electric vehicle market.
Despite the constant infusion of tens of millions of dollars, the company was never able to establish the production of batteries with stable characteristics - the indicators floated from instance to instance. If the company had more time and funding, it might not have had to sell equipment, patents and go under the wing of another energy company, A123 Systems, in 2012.
Lithium metal batteries- not news: they include any non-rechargeable lithium battery. SolidEnergy went into the creation of rechargeable lithium metal cells. The new product has twice the energy capacity of lithium-cobalt batteries. That is, in the previous volume, it was possible to fit twice as much energy. Instead of traditional graphite at the cathode, they used lithium metal foil. Until recently, lithium metal batteries were extremely explosive due to the growth of dendrites (tree-like metal formations growing on the anode and cathode), which led to a short circuit, but the addition of sulfur and phosphorus to the electrolyte helped to get rid of dendrites (although SolidEnergy does not yet have the technology). In addition to the very high price, among the known problems of SolidEnergy batteries is a long charge - 20% of the capacity per hour.
Comparison of the sizes of lithium metal and lithium ion batteries of equal capacity. Source: SolidEnergy Systems.
Active work on magnesium-sulfur cells began in the 2010s, when Toyota announced research in this area. The anode in such batteries is magnesium (a good, but not equivalent analogue of lithium), the cathode consists of sulfur and graphite, and the electrolyte is a normal NaCl salt solution. The problem with the electrolyte is that it destroys sulfur and makes the battery inoperative, so the electrolyte had to be filled just before use.
Toyota engineers have created a non-nucleophilic particle electrolyte that is non-corrosive to sulfur. As it turned out, a stabilized battery still cannot be used for a long time, since after 50 cycles its capacity drops by half. In 2015, a lithium-ion additive was integrated into the battery, and two years later, the electrolyte was renewed, bringing the battery life to 110 cycles. The only reason why work continues on such a capricious battery is its high theoretical energy capacity (1722 Wh / kg). But it may turn out that by the time successful prototypes appear, magnesium-sulfur elements will no longer be needed.
Generation instead of storing energy
Some researchers propose to go from the opposite: not to store, but to generate energy directly in the device. Is it possible to turn a smartphone into a small power plant? Over the past decade, there have been several attempts to save gadgets from the need for recharging via the mains. Judging by the way we now charge smartphones, the attempts were unsuccessful - recall the most "successful" inventions.
Direct Decomposition Methanol Fuel Cell (DFMC). Attempts to introduce methanol fuel cells into mobile technology began in the mid-2000s. At this time, the transition from long-lived push-button phones to demanding smartphones with large screens was taking place - they had lithium-ion batteries for a maximum of two days of operation, so the idea of instant recharge seemed very attractive.
In a fuel cell, methanol is oxidized to carbon dioxide on a polymer membrane acting as an electrolyte. The hydrogen proton goes to the cathode, combines with oxygen and forms water. A nuance: for the reaction to proceed effectively, a temperature of about 120 ° C is needed, but it can be replaced with a platinum catalyst, which naturally affects the cost of the element.
It turned out to be impossible to fit the fuel cell into the body of the phone: the fuel compartment was too big. Therefore, by the end of the 2000s, the DFMC idea took shape in the form of portable batteries (power banks). In 2009, Toshiba launched a serial methanol power bank called Dynario. It weighed 280 g and was similar in size to modern portable 30,000 mAh batteries, that is, it was palm-sized. The Dynario was priced at an impressive $ 328 in Japan, and another $ 36 for a set of five 50ml methanol vials. One "refueling" requires 14 ml, its volume was enough for two charges of a push-button phone via USB with a current of 500 mA.
Video demonstrating the refueling and operation of the Toshiba Dynario:
The matter did not go further than the release of an experimental batch of 3,000 copies, because the fuel power bank turned out to be too controversial: it is expensive in itself, with expensive consumables and the high cost of one phone charge (about $ 1 for a push-button). In addition, methanol is poisonous and in some countries requires a license to sell and even purchase it.
Transparent solar panels. Solar panels are an excellent solution for extracting endless (in our lifetime) solar energy. These panels have low efficiency at a high cost and too low power, while they are the easiest way to generate electricity. But the real dream of mankind is transparent solar panels that could be installed instead of glass in the windows of houses, cars and greenhouses. So to say, combine business with pleasure - generating electricity and natural lighting of the space. The good news is that transparent solar panels do exist. The bad news is that they are practically useless.
The developer and the University of Michigan showcases a transparent panel without a frame. Source: YouTube / Michigan State University.
In order to "catch" photons of light and turn them into electricity, the solar panel, in principle, cannot be transparent, but the new transparent material can absorb UV and IR radiation, transferring everything to the infrared range and diverting it to the edge of the panel. Conventional silicon photovoltaic panels are installed around the edges of the transparent panel as a frame, which capture the diverted light in the infrared range and generate electricity. The system works only with an efficiency of 1-3% … The average efficiency of modern solar panels is 20%.
Despite the more than dubious effectiveness of the solution, the famous watch manufacturer TAG Heuer announced in 2014 the premium push-button telephone Tag Heuer Meridiist Infinite, in which a transparent solar panel from Wysis was installed over the screen. Even during the announcement of the solution for smartphones, Wysis promised the power of such a solar charging of the order of 5 mW from 1 cm2 of the screen, which is extremely small. For example, this is only 0.4 W for the iPhone X screen. Considering that the bundled Apple smartphone adapter is scolded for obscenely low power of 5 W, it is clear that you cannot charge it with 0.4 W.
By the way, even if it didn't work out with methanol, hydrogen fuel cells got a ticket to life, becoming the basis of the Toyota Mirai electric car and Toshiba mobile power plants.
And what happened: successful experiments with Li-Ion
Success was achieved by those who were not eager to turn the world around at all costs, but simply worked to improve individual characteristics of batteries. Changing the cathode material greatly affects the voltage, energy capacity and life cycle of batteries. Next, we will talk about the established developments, which once again confirm the versatility of lithium-ion technology - for each “revolutionary” development there is a more efficient and cheaper existing analogue.
Lithium Cobalt (LiCoO2, or LCO). Working voltage: 3.6 V, energy capacity up to 200 Wh / kg, lifespan up to 1000 cycles. Graphite anode, lithium-cobalt oxide cathode, classic battery described above. This combination is most often used in batteries for mobile technology, where a high energy density per unit volume is required.
Lithium-manganese (LiMn2O4, or LMO). Working voltage: 3.7 V, energy capacity up to 150 Wh / kg, lifespan up to 700 cycles. The first effective alternative formulation was developed even before the sale of lithium-ion batteries as such. A lithium-manganese spinel was used at the cathode, which made it possible to reduce the internal resistance and significantly increase the output current. Lithium-manganese batteries are used in demanding equipment, such as power tools.
Lithium Nickel Manganese Cobalt (LiNiMnCoO2, or NMC). Working voltage: 3.7 V, energy capacity up to 220 Wh / kg, lifespan up to 2000 cycles. The combination of nickel, manganese and cobalt turned out to be very successful, the batteries increased both the energy intensity and the power of the given current. In the same "banks" 18650 capacity has risen to 2800 mAh, and the maximum output current - up to 20 A. NMC-batteries are installed in most electric vehicles, sometimes diluting them with lithium-manganese cells, since such batteries have a long life.
The new NMC battery of the Nissan Leaf electric car, according to the manufacturer's calculations, will live for 22 years. The previous LMO battery had a lower capacity and wore out much faster. Source: Nissan.
Lithium Iron Phosphate (LiFePO4, or LFP). Operating voltage: 3.3 V, energy capacity up to 120 Wh / kg, lifespan up to 2000 cycles. The compound, discovered in 1996, helped increase the amperage and lifespan of lithium-ion batteries to 2,000 charges. Lithium-phosphate batteries are safer than their predecessors, better withstand recharge. But their energy intensity is not suitable for mobile technology - when the voltage rises to 3.2 V, the energy intensity decreases at least twice as compared to the lithium-cobalt composition. But on the other hand, LFP exhibits less self-discharge and has a special endurance to low temperatures.
An array of lithium phosphate cells with a total capacity of 145.6 kWh. Such arrays are used to safely store energy from solar panels. Source: Yo-Co-Man / Wikimedia.
Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2, or NCA). Working voltage: 3.6 V, energy capacity up to 260 Wh / kg, lifespan up to 500 cycles. It is very similar to an NMC battery, has an excellent energy capacity, a nominal voltage of 3.6 V suitable for most equipment, but the high cost and modest life (about 500 charge cycles) do not allow NCA batteries to beat competitors. So far, they are only used in a few electric vehicles.
Autopsy video of the holy of holies - NCA battery cells of the Tesla Model S electric vehicle:
Lithium titanate (Li4Ti5O12, or SCiB / LTO) … Operating voltage: 2.4 V, energy capacity up to 80 Wh / kg, lifespan up to 7000 cycles (SCiB: up to 15000 cycles). One of the most interesting types of lithium-ion batteries, in which the anode consists of lithium titanate nanocrystals. The crystals helped to increase the surface area of the anode from 3 m2 / g in graphite to 100 m2 / g, that is, more than 30 times! The lithium titanate battery charges up to full capacity five times faster and delivers ten times the current than other batteries. However, lithium titanate batteries have their own nuances that limit the scope of batteries. Namely, the low voltage (2.4V) and the energy consumption are 2-3 times lower than that of other lithium-ion batteries. This means that in order to achieve the same capacity, the lithium-titanate battery must be increased in volume several times, which is why it cannot be inserted into the same smartphone.
SCiB-module manufactured by Toshiba with a capacity of 45 Ah, a nominal voltage of 27.6 V and a discharge current of 160 A (pulsed up to 350 A). Weighs 15 kg, and is about the size of a shoebox: 19x36x12 cm. Source: Toshiba.
But lithium-titanate batteries were immediately registered in transport, where fast charging, high currents during acceleration and resistance to cold are important. For example, electric cars Honda Fit-EV, Mitsubishi i-MiEV and Moscow electric buses! At the start of the project, Moscow buses used a different type of battery, which caused problems in the middle of the first journey along the route, but after the installation of Toshiba lithium-titanate batteries, there were no more reports of dead electric buses. Toshiba SCiB batteries, thanks to the use of titanium-niobium in the anode, restore up to 90% capacity in just 5 minutes - an acceptable time for a bus to park at the final stop where there is a charging station. The number of charge cycles that the SCiB battery can withstand exceeds 15,000.
Toshiba Lithium Titanate Battery Leak Test. Will it light up or not?
Energy Singularity
For more than half a century, mankind has dreamed of fitting in batteries the energy of the atom, which would provide electricity for many years. In fact, back in 1953, a beta-voltaic cell was invented, in which, as a result of the beta decay of a radioactive isotope, electrons converted semiconductor atoms into ions, creating an electric current. Such batteries are used, for example, in pacemakers.
What about smartphones? Yes, so far nothing, the power of atomic elements is negligible, it is measured in milliwatts and even microwatts. You can buy such a battery even in an online store, however, even the notorious wristwatch will not work from it.
How long to wait for atomic batteries? Please City Labs P200 - 2.4 V, 20 years of service, however, the power is up to 0.0001 W and the price is about $ 8000. Source: City Labs.
More than 10 years have passed since the invention of stable lithium-ion batteries to the start of their serial production. Perhaps one of the next news about a breakthrough power source will become prophetic, and by the 2030s we will say goodbye to lithium and the need to charge phones every day. But so far, it is lithium-ion batteries that are driving progress in wearable electronics and electric vehicles.
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