Technology to improve battery performance in terms of weight and cost

Technology to improve battery performance in terms of weight and cost

Many types of batteries have higher mass energy density levels than lead-acid batteries. But it costs more, many have poorer performance, and some can lead to higher safety and environmental risks. For example, the search for the “ideal” electric vehicle or hybrid vehicle battery is an optimization problem: what kind of battery technology can provide the best combination of performance, reliability, longevity, adequate safety, and the lowest environmental risk cost .

Different application fields have different special restrictions on batteries. In order to achieve the best performance at the minimum cost under given application conditions, it is necessary to conduct trade-off studies on key battery parameters. In addition, the performance of the battery cannot be expressed by any single design parameter, and the key performance parameters are often interrelated. For example, a cost-effective way to improve the power performance of a battery is to use thinner electrodes, which will reduce the volumetric energy density and lifetime. This means that thinner electrodes are not suitable for rechargeable batteries whose main performance requirements are volumetric energy density and lifetime, such as space systems and hybrid vehicles. For example, a standard liquefied gas tank in a car can hold about 60L or 15gal (1gal=4.54609L) of fuel and weigh about 50kg or 331b (1lb=0.435592kg). If a lead-acid battery pack large enough to provide the same mileage or distance is used, the weight of this battery will exceed the car itself (over 2t), and the space occupied will be equivalent to the passenger compartment. If an electric vehicle chooses a lithium battery pack, the battery pack will require at least 144 batteries with the smallest weight and size. If the car is involved in a rear-end collision, the replacement of the lithium battery pack will cost more than $8,000. In short, to build a practical electric vehicle, energy storage requirements, battery pack size, and cost must be carefully weighed against possible factors. The design procedures and parameters of the battery and the vehicle are interdependent. Electric vehicles define the performance envelope of a usable battery, and the range of battery performance that can be achieved at any point in time limits the range of electric vehicles and the number of kilometers that they can travel without charging the battery.
This interdependence has a bad side effect, that is, battery performance goals often change.

Technology to improve battery performance in terms of weight and cost
Electric car battery

Because a perfect battery is impossible to achieve in actual practice, the design process of electric vehicles tends to change with the prediction of battery performance. The wide range of data in Table 1 blurs the actual difference between the requirements for lead-acid batteries used in electric and hybrid vehicles. In general, the energy capacity of hybrid vehicle batteries is smaller than that of electric vehicles, but they will need to generate more electricity per unit mass or volume, as listed in Table 1. Note that the battery of a hybrid electric vehicle can be charged from an on-board power supply or an AC power supply, and often only runs on a small part of its capacity in thousands of cycles.

Performance parameterBattery
Battery
Typical lead-acid battery
electric carHybrid Electric car
Mass energy density/(W·h/kg)85 ~ 2008 ~8025 ~40
Volume energy density/(W·h/L)
130 ~ 30010 ~ 10030 ~ 70
Specific power/(W/kg)80 ~ 200600 ~ 160080 ~ 100
Average life/(cycle/year)600 ~ 1000/5 ~ 10100 ~ 105/5 ~1200 ~ 400/2 ~5
Cost/(S/(W·h))100 ~150175 ~ 100060 ~ 100
Table 1 Performance targets of electric and hybrid electric vehicles

The data given in Table 1 are estimated values ​​of various parameters, with an error of ±10%. The manufacturing technology of lead-acid batteries has been highly optimized, the key electrochemical components of lead and sulfuric acid are relatively cheap, and non-lead-acid batteries continue to undergo design changes due to changes in material technology and material costs.