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• 191.

  What are EV batteries encased in?

  Electric vehicle batteries are usually encapsulated in protective cases to ensure their safety, stability and service life. The casing of an electric vehicle battery serves several critical functions, including preventing physical damage, isolating temperature changes, and containing any potential hazards.

  Common materials used to encapsulate electric vehicle batteries include:

  ① Steel: Often used in the construction of battery cases due to its durability and ability to provide structural integrity, protecting the battery from impacts and other external forces.

  ② Aluminum: This lightweight metal is also used in certain situations, especially parts that require a balance between strength and weight. It helps maintain the overall weight of the vehicle while providing a level of protection for the battery.

  ③ Thermoplastic materials: These materials provide impact resistance and the ability to absorb energy in the event of an accident. They can be molded to fit specific shapes and are often combined with other materials to provide extra protection.

  ④ Composites: These materials, such as carbon fiber composites, have high strength-to-weight ratios and are increasingly used in the construction of battery enclosures to reduce weight while maintaining structural integrity.

  ⑤ Ceramics: Some advanced battery casings may use ceramics because ceramics have heat resistance and excellent heat insulation properties. Ceramic materials can help manage the temperature of the battery, ensuring optimal performance and longevity.

  The choice of enclosure material depends on a variety of factors, including cost, weight, structural requirements, safety considerations and overall performance goals. Manufacturers carefully select materials to ensure that the battery casing provides adequate protection for the sensitive components inside the battery pack.
  
• 192.

  How does a battery charge and discharge at the same time?

  It is impossible for a battery in the traditional sense to charge and discharge at the same time because it is the opposite process. Charging involves the flow of electrons into the battery, while discharging involves the flow of electrons out of the battery to power a device or system. However, in some complex systems, due to the nature of system operation, the battery may charge and discharge simultaneously.
  
  For example, in a hybrid electric vehicle (HEV) or a plug-in hybrid electric vehicle (PHEV), the battery can be charged through regenerative braking, where the kinetic energy of the vehicle's motion is converted into electrical energy and stored in the battery. At the same time, the battery supplies power to the vehicle's electric motor during acceleration or other driving conditions, causing the battery to discharge.
  
  In this case, the battery does not really charge and discharge at the same time in the traditional sense but rapidly alternates between these states to promote the efficient operation of the entire system. Specialized control systems and circuits manage the current flow to ensure that charging and discharging processes occur in a coordinated manner without causing damage to the battery or connected devices.
  
• 193.

  Why is battery charging slower than discharging?

  Batteries can charge and discharge at different rates, but generally charge more slowly than discharge for the following reasons:
  
  ① Chemical reactions: During the charging process, chemical reactions must occur inside the battery to store energy, and these reactions usually take longer to complete than the reactions involved in discharging. Discharging involves converting stored chemical energy into electrical energy, which occurs faster than the chemical processes involved in charging.
  
  ② Internal resistance: The battery has internal resistance, which will cause the voltage to drop during discharge. However, during charging, the charging voltage needs to overcome this resistance, which results in a slower charging rate than the discharging rate.
  
  ③ Heat dissipation: Charging generates more heat within the battery due to the nature of the chemical reactions involved. This heat needs to be dissipated efficiently to prevent damage to the battery. Slower charging helps control temperature rises, prevents overheating and ensures battery safety and longevity.
  
• 194.

  What is the depth of discharge of EV battery?

  Depth of discharge (DOD) refers to the proportion of a battery's used capacity relative to its total capacity. In electric vehicle (EV) batteries, depth of discharge indicates how much of the total energy stored in the battery has been utilized before charging. The recommended depth of discharge for electric vehicle batteries is usually kept within a specific range to ensure longevity and optimal performance of the battery over its lifetime.
• 195.

  Do EV batteries discharge?

  Yes, EV (electric vehicle) batteries discharge even when the vehicle is not in use. This discharge, often called "self-discharge," is a natural phenomenon that occurs due to various internal chemical processes within the battery. While EV batteries have a relatively low self-discharge rate compared to some other battery types, it can still occur over time.