There are two kinds of batteries for the electric boat engine, which are lead-acid battery and lithium battery. They have unique features from the perspectives of weight energy density, volumetric energy density, service life, price, applicability, national policy, etc.
The current lithium battery energy density is generally 200-260 wh / g, lead acid is generally 50-70 wh / g. The weight energy density lithium battery is 3-5 times than the lead acid. It means in the same capacity, the weight of the acid battery is 3-5 times that of the lithium battery. So the lithium battery has an absolute advantage in the weight reduction of the energy storage device. The volume capacity density of a lithium battery is usually about 1.5 times that of a lead-acid battery. So in the case of the same capacity, the lithium battery is about 30% smaller than the lead-acid battery. At present, the more popular material systems are ternary and iron-lithium. The number of cycles of ternary power lithium batteries is usually more than 500 times. The number of cycles of lithium iron phosphate batteries is more than 600 times. And the number of cycles of lead-acid batteries is usually only 300-350. So the life of a lithium battery is about 1-2 times that of a lead-acid battery.
But so far, lead-acid batteries are still used in some large-scale machines, such as cars and rubber boats for fishing. According to the survey, 86% of customers choose to use lead-acid batteries. The lithium battery is light in weight, small in size, and has a long life cycle. But why do people still use lead-acid batteries?
1. Good applicability
The lead-acid battery has good low-temperature performance and high current performance. When discharging at 10C rate at -10 ° C temperature, the voltage above 10V can be held longer than 90s. It is enough to cope with harsh environment in most areas. While the low-temperature performance of lithium-ion batteries is much worse. The discharge performance at low temperatures will be drastically attenuated. And it is difficult to achieve practical applications in low-temperature areas. Secondly, the high current characteristics, the instantaneous current is relatively large when the motor starts up. And the high power motor may be higher. As for the current positive and negative materials of lithium ion battery, graphite and lithium cobalt oxide, neither of them belongs to the high-power anode material. The performance is drastically lowered at high power. So, lithium batteries are not suitable for use in low temperature environments. While lead acid batteries will perform much better in this areas.
2. Good safety
The safety of lead-acid batteries is extremely high in current battery systems.
1) The high current performance means that the battery is not prone to accidents.
2) Even in the event of an accident, the positive and negative materials are lead compounds. The electrolysis liquid is also a sulfuric acid solution. They are not flammable, and can only cause the surrounding parts to burn. The negative electrode material of the lithium ion battery is graphite, and one kind of carbon material is a flammable substance. The electrolyte is an ester solvent and a lithium salt. The ester solvent is not only flammable but also extremely volatile. Once a large amount of heat is released or is likely to be burned or even exploded during a collision, collisions are inevitable when driving a ship. Once the consequences of the explosion are unimaginable.
3) Lithium-ion batteries tend to form lithium dendrites in the negative electrode during high-current discharge. Causing internal short-circuit and explosion of the battery. It is a consensus in the lithium battery industry. In fact, many other problems exist. One big problem is the stability of the electrode material, caused by the long-term high state of charge (SOC) of the battery.
3. Low cost
The cost of lead-acid batteries is undoubtedly the lowest. The requirements for electrode materials, electrolytes or assembly environment are much lower than lithium-ion batteries. In the case of the same capacity, the prices of the lithium battery is about 3-5 times than that of the lead-acid battery. The money used for buying a lithium battery can buy 3-5 lead-acid batteries. Although the lithium battery is lasting, but still far from meeting the requirements of customers.
4. High recycling
People said that lead-acid batteries polluted the environment, lithium-ion batteries were environmental friendly. In fact, this is a big misunderstanding. At present, the best part of lead-acid batteries is the recycling mechanism. Lead-acid batteries are now used in the field of engines and start-up power supplies. These two areas are highly targeted, that is, users return to special stores to change batteries when changing batteries. Why? You can exchange old batteries into money and buy new ones! The lithium-ion battery contains less heavy metals. Only the positive electrode material contains cobalt metal. But it has a large user volume in the world. In the long run, this is still a problem, but there is no mechanism paying attention to this issue, no mechanism recycling lithium batteries.
In summary, although the lithium battery is small in size, light in weight, and long in service life, it is still used in mobile phones, tablets, and computer batteries. For large devices, they currently in the market use lead-acid batteries. In terms of applicability, safety and cost, lead-acid batteries are still superior to lithium batteries as an energy source for electric boat engine.