Lithium boat batteries demand and development

In November 2020, Mazarin’s Silent 5503 was launched at Qingdao Yangfan Terminal Center with a 230kwh high-voltage Lithium boat batteries pack on board, the vessel can reach a maximum speed of 20kt at full load and can run for 6 hours at an economic speed of 6-8kt.

Electric boats and lithium boat batteries

Electric-powered boats have been around for nearly a century. From the 1880s to the 1920s, electric boats were very popular. Due to the technical limitation at that time, the speed regulation technology of AC motor was not mature, and mostly DC electric propulsion was used, which had simple speed regulation system and good speed regulation performance, but the DC motor had complicated structure, large volume and weight, and had problems of power and speed limit, which could only be applied on engineering ships and submarines.

Since the 1980s, with the rapid development of power electronics technology, high-power AC motor frequency conversion and speed control technology has become increasingly mature, based on thyristor rectifier/inverter scheme and IGBT device scheme to achieve the rapid development of ship electric propulsion technology in foreign countries, and in terms of reliability and efficiency have a breakthrough, so that the application areas of electric propulsion technology continues to expand, in addition to the application of icebreakers, dredgers, ferries, but also widely used in large and medium-sized conventional ships.

The prospect of lithium boat batteries applied to ship electric propulsion system is one of the favored power units. It is characterized by long life, good cycle performance, small size and no pollution. In addition, Lithium boat batteries has high energy density, can maintain a long time discharge state, has good stability performance.

For ship electric propulsion system, how to reduce fuel consumption, system maintenance cost, harmful gas emission and increase the stability and reliability of the whole ship has been the focus of researchers’ research. Lithium boat batteries packs can provide continuous high power output, providing a better option for ship system integration and design, thus reducing the complexity of the system and unnecessary expenses.

Domestic electric boat development status

Our country is vast and has many water systems. Nowadays, many rivers are between the banks of rivers, or small islands in the middle of lakes due to the booming demand of people’s life and tourism, and the traffic volume is very high. Water traffic inevitably brings emissions. According to the “White Paper on Air Pollution Prevention and Control in Chinese Ships and Ports”, the sulfur content of marine fuel oil is 100 to 3,500 times higher than that of automotive diesel. The operation of ships brings more air pollution than vehicles.

The pure lithium boat batteries driven electric vessel is a good solution to the above contradiction. Most of the domestic small motorized inland river vessels are 5-20 m long, with total installed capacity below 2,000 kW and propulsion power below 1,500 kW. 95% of them adopt the propulsion method of diesel engine with gearbox driven propeller.

As a result, the promotion and application of electric propulsion system for small inland waterway vessels is flourishing. The power supply mode is based on lithium boat batteries and supplemented by super capacitor. When the propulsion system needs instantaneous strong power, the super capacitor supplies energy; when the system needs stable power output, it is supplied by lithium boat batteries; when the system has energy return (emergency braking or reversing), the super capacitor is responsible for absorbing instantaneous return energy. Since the super capacitor and the shore power stored in the battery are used, no fuel is consumed during operation and there is no pollution, so the pure electric boat is a veritable “green boat”. The pure electric boat provides a new idea and solution for the pollution prevention in inland waters.

Lithium-ion batteries generally use lithium alloy metal oxide as the positive electrode material, graphite as the negative electrode material, and a non-aqueous electrolyte. Lithium boat batteries has high energy density, small size, light weight, long cycle life, no memory effect, small self-discharge rate, high voltage of single cell, and is the best new environmentally friendly battery, which is widely used in cell phones, computers, cameras and electric transportation. However, Lithium boat batteries have poor resistance to overcharge and discharge, and are prone to explosion and other dangerous situations when operated improperly.

The marine environmental technical conditions that Lithium boat batteries must meet include the following:

(1) Adapt to vibration and shock. Vibration can make the fixed or connected parts of electrical equipment loosened, so that the structure of the components damage or malfunction. So there should be anti-loosening measures, vibration damping or vibration isolation measures, with a solid vibration-resistant and shock-resistant mechanical structure.

(2) Adaptation to tilt and sway. Continuous tilting and swaying disrupts the balance of forces in the normal resting position, creating additional forces on moving parts and leading to equipment failure or damage.

(3) Adapt to the ambient temperature. Ambient temperature has an important impact on the performance and service life of electrical equipment. Ambient temperature includes air temperature and seawater temperature.

(4) Adapt to the environment of humidity, salt spray, oil mist and mold. Humidity of the ambient air, salt spray, oil mist and mold make electrical equipment insulation material insulation performance, so that metal parts rust and corrosion. Humid salt spray in the insulating material surface to form a moist leakage film, in the hot and humid conditions mold secretion of organic acids, intensified the surface of the moisture. Oil mist and dust adhering to the surface increases the surface leakage, and hinders heat dissipation to increase the temperature. Moist water molecules penetrate into the cracks and capillaries of the insulation material, increasing leakage current, which leads to a decrease in insulation resistance. Many electrical equipment damage is often caused by the thermal breakdown of the insulation material. As the temperature exceeds a certain limit, it will accelerate the aging of the insulation material and lose insulation performance. Therefore, marine cables, wires, windings, etc. should be used with higher heat-resistant grade of moisture resistance, salt spray resistance, anti-mold insulation materials, to use good flame retardant, good mechanical strength and corrosion-resistant materials.

(5) Adaptation to changes in voltage and frequency of the ship’s power grid. The ship power system is an independent and limited grid. Both voltage and frequency are affected by load variation, so the range of voltage and frequency variation is specified to be able to work effectively within this range.

(6) Protection requirements. In order to avoid the intrusion of external solid and liquid foreign body electrical equipment failure or damage, thus causing fire hazards, general electrical equipment should have protective shell cover.

To ensure the requirements of safe navigation, the ship must store enough power energy to meet the range requirements before each sailing. However, since the ship cannot use up all the electrical energy stored in the battery after each return voyage, the selected power battery must have no memory effect to meet the design requirements. Therefore, ion batteries are the ideal choice of Lithium boat batteries for electric ships.