Comparative analysis of hydrogen fuel cells and lithium batteries

Lithium battery

A "lithium battery" is a type of battery using a lithium metal or a lithium alloy as a negative electrode material and using a nonaqueous electrolyte solution. Lithium metal batteries were first proposed and studied by Gilbert N. Lewis in 1912. In the 1970s, M.S.WhitTIngham proposed and began researching lithium-ion batteries. Due to the very active chemical properties of lithium metal, the processing, storage and use of lithium metal are very demanding on the environment. Therefore, lithium batteries have not been used for a long time. With the development of science and technology, lithium batteries have become the mainstream.

Lithium batteries can be roughly divided into two categories: lithium metal batteries and lithium ion batteries. Lithium-ion batteries do not contain metallic lithium and are rechargeable. The fifth-generation lithium-metal battery of rechargeable batteries was born in 1996, and its safety, specific capacity, self-discharge rate and performance price ratio are better than lithium-ion batteries. Due to its own high technical requirements, only a few companies in the country are producing such lithium metal batteries.

Hydrogen fuel cell and lithium battery analysis

Hydrogen fuel cell

A hydrogen fuel cell is a battery that uses hydrogen as a chemical element to store energy. The basic principle is the reverse reaction of electrolyzed water, which supplies hydrogen and oxygen to the anode and cathode respectively. After hydrogen diffuses outward through the anode and reacts with the electrolyte, the electrons are released to the cathode through an external load.

Hydrogen fuel cell features Non-polluting fuel cells are environmentally friendly. It is through electrochemical reactions, not combustion (steam, diesel) or energy storage (battery) - the most typical traditional backup power solution. Combustion releases pollutants such as COx, NOx, SOx gas and dust. As mentioned above, fuel cells only produce water and heat. If hydrogen is produced by renewable energy sources (photovoltaic panels, wind power generation, etc.), the entire cycle is a complete process that does not produce harmful emissions.

The noise-free fuel cell is quiet and the noise is only about 55dB, which is equivalent to the level of normal conversation. This makes the fuel cell suitable for indoor installation or where there is a limit to noise outdoors.

The efficiency of high-efficiency fuel cells can reach more than 50%, which is determined by the conversion properties of fuel cells. It directly converts chemical energy into electrical energy without intermediate transformation of thermal energy and mechanical energy (generator).

Hydrogen fuel cell and lithium battery analysis

Comparative analysis of hydrogen fuel cells and lithium batteries

The global energy landscape is nearing the eve of the big change

Throughout human history, the progress of civilization is essentially the progress of energy output intensity. In the early agricultural civilization, the power was mainly based on human and livestock, wood and other bio-energy. The output power was very limited. It was also limited by the land carrying capacity. The economy could only circulate at a low level, after the industrial revolution in the 18th century, with the steam engine and the internal combustion engine. Promote, the basic energy has become fossil energy represented by coal and oil, the energy density has increased by hundreds of times, and GDP has finally broken through the shackles of the “Malthus trap”, showing an exponential growth. At present, the global energy structure is 33% crude oil, 24% natural gas, 30% coal, 4%special power, 7% hydropower and 2% new energy. Fossil energy is in an absolute dominant position. But looking to the future, we judge that the human energy structure has reached the eve of another major change, and oil is expected to be completely replaced within 30 years. Hydrogen energy represented by fuel cells will become the new leading energy source!

The oil era will be fully replaced

The biggest problem facing the development of agricultural civilization in the late stage is that limited land resources ultimately cannot support further population growth. As a non-renewable resource, fossil energy is also facing the constraints of resource scarcity. According to the linear extrapolation of consumption growth over the past 20 years, the global proven oil reserves can only support 30 years. Even if technological advancement can extend the life of oil for decades, it is still a day of useful light, relative to human beings. The history that lasted for at least a thousand years still has no meaning. Moreover, considering that the current level of exploration is already sufficient, the probability of discovering low-cost large oil fields is very low, and the mining cost of potential supply will become higher and higher. This will eventually stimulate the rapid acceleration of the commercialization of alternative energy sources. For example, the development of lithium battery vehicles is now in full swing, so the economic oil depletion may come earlier. In the future, who can completely replace oil and become a new generation of vehicle fuel becomes a very critical issue.

Fuel cell vs lithium battery who will win

At present, the mainstream technical route for replacing petroleum vehicles is lithium batteries and fuel cells. The biggest advantage of fuel cells is the high energy density, which is 120 times that of lithium batteries. However, the lithium battery started early, the degree of commercialization is higher, the cost of the whole vehicle is lower, and the charging can utilize the existing power grid system. Compared with the supporting network of the entire hydrogenation and hydrogen supply of the fuel cell, the construction must be started from scratch, and the cost must be lower. Therefore, the core of competition between the two is the competition of energy density vs. cost. The cost reduction is an engineering problem that can be solved by commercialization, while the energy density faces the bottleneck in the basic science field, basically no solution. Therefore, the difference between the two is essentially the difference between “dao and technology”. In the long run, fuel cells will undoubtedly have greater potential and are also expected to become the next generation of basic energy for vehicles.

Energy density increase is the main line logic

Every successful energy revolution in human history has a clear main line of logic, which is an order of magnitude increase in energy density. If coal is 160 times higher than firewood, oil is 2 times higher than coal. New energy can only subvert the perfect basic network and industrial supporting established by long-term development, and reversed its huge use inertia, only with the advantages of compaction of energy density. This is similar to the 10x speed principle proposed by the founder Grove in the IT field, that is, once the new technology that can be successfully subverted appears, it is basically a spark, and it is unstoppable. For example, gasoline vehicles are 20 years later than electric vehicles. Early technology is also more immature, but with the advantage of high energy density, it has replaced electric vehicles.

Hydrogen fuel cell and lithium battery analysis

In recent decades, although countries are vigorously promoting electric vehicles, their proportion is still very low, still less than 1%. The core is that the past electric vehicles have violated the main line logic of energy density improvement. Even the latest generation of lithium-ion battery cars, the extreme energy density is only 1/40 of gasoline the industry naturally cannot improve 10 times faster. But the emergence of fuel cells has completely changed the status quo. It uses hydrogen as raw material, the basic energy density is three times that of gasoline, the work efficiency of the motor is twice that of the internal combustion engine, and the actual density is six times that of gasoline. Moreover, from the history of human energy evolution in the past century, it is essentially the history of adjustment of hydrocarbon ratio. The higher the hydrogen content, the higher the energy density. The future shift from carbon energy to hydrogen energy is the trend of the times. Therefore, fuel cells using hydrogen energy are undoubtedly It is more representative of the direction of historical development and is most likely to become the basic energy source for the next generation.

The performance of the motor vehicle is mainly the endurance, charging/charging time, output power and safety. The energy density of fuel cells is much higher than that of lithium batteries. The corresponding battery capacity, fast charge capacity and cruising range have a natural advantage, even if it is compared with the top-grade luxury car Tesla of lithium batteries. However, its power density is not high, and the maximum output power depends on the auxiliary power battery system. The corresponding maximum speed and 100-kilometer acceleration index and lithium battery are not much different. For the sake of comparison, we select the current mainstream 2L exhaust gas gasoline vehicle, which corresponds to the 45-degree lithium battery vehicle and the output power 100KW fuel battery vehicle as the analytical benchmark.

Energy density comparison

As a kind of battery, lithium battery is a closed system. The battery is only the carrier of energy. It must be charged in advance to run. The energy density depends on the energy density of the electrode material. Since the energy density of the negative electrode material is much larger than that of the positive electrode at present, increasing the energy density requires continuously upgrading the positive electrode material, such as from lead acid, to nickel, to lithium batteries. However, lithium is already the metal element with the smallest atomic weight. The cathode material with better lithium ion is theoretically only pure lithium electrode, but the energy density is only 1/4 of that of gasoline, and the commercial technology is extremely difficult. There is no hope of breaking through. Therefore, the increase in energy density of lithium batteries is subject to theoretical bottlenecks, and the space is very limited. At most, it is increased from the current 160Wh/KG to 300Wh/KG. Even if it reaches only 1/120 of the fuel cell, it can be said that it is lost at the starting line.

Volume energy density comparison

The main disadvantage of the fuel cell's raw material hydrogen is that the volumetric energy density is not high. Now, basically, pressurization is used to solve this problem. According to the current pressurized mode of 700 atmospheres, the volumetric energy density is 1/3 of gasoline. Also running 300 kilometers, the fuel cell hydrogen storage tank volume is 100L, the weight is 30KG, corresponding to the gasoline vehicle fuel tank is 30L, but the motor volume is 80L smaller than the internal combustion engine, the total volume is not much different. Lithium battery vehicles are divided into two main technical routes: ternary and lithium iron phosphate. Representative companies are Tesla and BYD. The ternary energy density is higher, but the safety is poor. The auxiliary safety protection equipment is needed. The two batteries required to run 300 kilometers are 140L and 220L respectively, and the weight is 0.4 tons and 0.6 tons, which are much higher than the fuel cells. Looking into the future If the hydrogen storage alloy and low-temperature liquid hydrogen storage technology can be broken, the fuel cell volume energy density will increase by 1.5 times and 2 times respectively, and the advantage will be more obvious.

Power density comparison

The fuel cell can be understood as a chemical power generation system using hydrogen as a raw material, so the output power is relatively stable. In order to maximize the discharge power, a power battery system must be added. For example, Toyota Mirai is a supporting nickel-hydrogen battery. However, as an open power system, its energy comes from external input. The additional Ni-MH battery does not need to consider the problem of energy storage. As long as it is 5-8 degrees, it can meet the demand and the battery life is not high in the case of limited use. Although the theoretical discharge efficiency of lithium batteries is very high, in order not to damage the battery life, there are many restrictions on use. In the case of full charge, it cannot be discharged at a large rate, and the rapid discharge is only applicable to the interval of 0-80%. Even so, at 5C rate discharge, the battery cycle life in the laboratory will be shortened to only 600 times, and will be further reduced to 400 times under real conditions. For example, even if Telsa has a maximum power of 310KW, the actual discharge rate is only 4C. . Moreover, lithium batteries are used as closed energy storage systems with low energy density, and high power discharge and high cruising range are basically difficult to be compatible unless the battery weight is greatly increased. Even though Tesla uses the current best-density ternary battery, its battery components weigh nearly half a ton.

Hydrogen fuel cell and lithium battery analysis

Security comparison

In addition to the above indicators, safety is undoubtedly critical for motor vehicles. As a closed energy system, lithium batteries are difficult to be compatible with in principle high energy density and safety, otherwise they are equivalent to bombs. Therefore, in the mainstream process route, the lithium iron phosphate with low energy density is better in safety, and the decomposition begins when the battery temperature reaches 500-600 degrees, and basically does not require too much protection auxiliary equipment. The ternary battery used by Telsa is high in energy density, but it is not resistant to high temperatures. It will decompose at 250-350 degrees and has poor safety. The solution is to connect more than 7000 batteries in parallel, which greatly reduces the risk of leakage from a single battery, and even the combination of a complex battery protection device. And several accidents occurred in the previous period, although thanks to Telsa's safety design, there were no casualties, but in terms of the accident itself, it was actually a very slight collision, and the body did not receive any damage, but the battery was on fire. It also reflects its natural disadvantages in terms of safety.

Fuel cells are generally worried about their safety due to the flammability and explosiveness of raw materials. However, as we have shown in the table below, the safety of hydrogen is not bad or even slightly better than the two common flammable gases for gasoline and natural gas. Nowadays, the vehicle hydrogen storage devices are made of carbon fiber materials, which can be made unscathed in the 80KM/h multi-angle collision test. Even if a car accident causes leakage, due to the high concentration of hydrogen explosion, it usually begins to burn before the explosion, but it is difficult to explode. Moreover, the hydrogen gas is light in weight, and the hydrogen in the overflow system will rise rapidly after the fire, but the body and passengers are protected to some extent. The gasoline is liquid, the lithium battery is solid, it is difficult to rise in the atmosphere, the combustion is at the bottom of the cabin, and the whole vehicle will quickly retire. The hydrogen storage and transportation link is very similar to LNG, but the pressure required is greater. As commercialization progresses, its overall safety is still controllable.

The cost of battery vehicles is mainly divided into vehicle cost, raw material cost and supporting cost. At present, the most common problem for fuel cells is that the cost is too high, but from the perspective of development, as technology advances and commercialization increases, there is a large room for cost reduction. If the lithium battery takes into account the cost of capacity expansion at the grid end, the overall supporting cost is still higher than that of the fuel cell. The specific calculation is as follows:

Vehicle cost comparison

Lithium batteries, fuel cells and traditional gasoline vehicles, the difference in overall vehicle costs is mainly reflected in the cost of the engine, and other components are not much different. The cost of a 2L petrol engine is about 30,000 yuan, and it is difficult to change much in the future. The current electricity cost of the lithium battery is 1,200 yuan / kWh, and it is expected to drop to 1,000 yuan / kWh in the future, 45-degree electric vehicle, the battery cost is 45,000 yuan. The fuel cell cost is mainly the battery pack and the high-pressure hydrogen storage tank. Now the 100kw battery is composed of 100,000 yuan. After the annual output is expected to be 500,000 units, the unit cost will be reduced to 30 US dollars / KW, that is, 20,000 yuan. The cost of the existing hydrogen storage tank is 60,000 yuan, and it is expected to drop to 35,000 yuan in the future, with a total cost of 55,000 yuan. In the long run, the cost of the three power systems is not much different. It can be seen that the cost of the whole vehicle is not the core issue.

Raw material cost comparison

The fuel consumption of a 2L petrol car is 10 liters per 100 kilometers, and the price of gasoline is 5.8 yuan/L. The cost is 58 yuan. The lithium battery car consumes 17 kilowatts per kilometer, and the cost is 0.65 yuan/kWh. The cost is 11 yuan. The fuel cell consumes 9 square meters of hydrogen per 100 kilometers. The hydrogen production method is mainly divided into electrolyzed water or chemical reaction, such as hydrogen production from coal and hydrogen production from natural gas. The cost of electrolyzed water is mainly electricity, with an average of 5 degrees of electricity and 1 square of hydrogen. The cost is about 3.8 yuan per square, but it can be directly electrolyzed at the hydrogen refueling station, saving transportation costs. If large-scale centralized production of fossil energy is used, the lowest domestic cost is coal-to-hydrogen, which is about 1.4 yuan/square. In North America, cheap natural gas can be used at a cost of 0.9 yuan/square. If we take the cost of coal gas as the standard, the cost of raw materials for 100 kilometers is 12.6 yuan, which is not much different from lithium batteries.

Matching cost comparison

The cost of hydrogen refueling station, gas station and charging station is mainly divided into land cost, equipment cost and construction cost. The difference is mainly reflected in equipment cost. The gas station is basically 3 million yuan, the charging station is 4.3 million yuan, and the hydrogen refueling station is based on the current Japanese standards.

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