Semco university – All about the Lithium-Ion Batteries

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Principles of power battery system design – Semco University

Basic principles of power battery system design

The selection of electric vehicle batteries is closely related to parameters such as capacity, internal resistance, battery type, and production specifications. When selecting a single battery, the performance parameters, safety, energy density of the single battery and the installation position, space, total energy and power of the battery pack should be considered. The following uses a case to describe the battery selection in detail.

Battery Pack Design Input:

  • Cruising range: 100 km
  • Energy consumption factor: 0.15 kWh/km
  • Drive voltage: DC 350 V (DC side voltage of drive motor and controller)
  • Continuous current: 1C output
  • P/E value: 5
  • Battery type: soft pack ternary lithium battery
  • Battery Specification: 20Ah / 3.6V

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Battery Pack Design Output:

ProjectParameterFormula
Total capacity of battery pack system≥ 15kWh= design mileage * energy consumption coefficient
Total battery pack system usable capacity≥ 12kWh= total capacity * SOC operating range
Battery pack system SOC operating range≥ 80%= 10% SOC~90%SOC
Battery system nominal voltageDC 350V= drive voltage
Battery system operating voltage rangeDC 287V~408V= 3V~4.2V
Battery system continuous charge/discharge power15 kW= 1C continuous output capability
Battery system peak charge/discharge power60kW @ 10s= P/E
Battery system operating temperature range0℃~60℃
Battery system cooling method
Battery system life8 years= 8 years or 100,000 km
Battery system self-discharge rateMay
Total weight of battery system≤ 150kg 

Module Design Output:

  • Number of module strings = driving voltage/battery rated voltage = 350V/3.6V ≈ 98 strings
  • Number of modules in parallel = total energy/number of strings/cell voltage/single capacity =15kWh/98 strings/3.6V/20Ah ≈ 2 parallels
  • Serial and parallel mode =
  • first parallel then serial
  • Serial-before-parallel

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Parallel First and then Serial:

In the parallel-before-series structure, the failure of a single battery automatically exits, except for the capacity reduction, it does not affect the use after parallel connection, and the parallel connection process is strict; when a unit battery in the parallel connection is short-circuited, the parallel circuit current is very large, which is usually avoided by adding fuse protection technology. Therefore, the scheme chooses the parallel process first and then the series process.

ProjectParameterRemark
The number of modules in series and parallel98 series 2 parallel 
Serial modeSerial first 
Module voltage range294V~411.6V 
Module rated voltage352.8V 
Module pressure800N ~ 1000N 

Battery Design Output:

ProjectParameterRemark
Battery TypeSoft pack ternary lithium battery 
Single battery voltage range3.0V ~ 4.2V 
Single battery capacity20Ah@1C
Single battery nominal voltage3.6V 
Cycle life≥ 3000 times@1C

In the battery module design process, the safety specification test parameter level of the battery module should be higher than the safety specification level of the battery pack to improve the reliability of the battery pack. The specific module requirements are as follows:

Module open circuit voltageThe OCV between the total positive and total negative of the measuring module for the mustimeter
Module cell voltageTest tooling to measure the OCV voltage of each string of batteries, ΔV≤5mV~10mV
Module DC internal resistanceThe device charges or discharges the module with a 3C rate of10s, and measures the DCIR
Module AC internal resistanceACR test the module at 1kHz
Module insulation resistanceThe total positive and total negative of the module to the insulation internal resistance between metals
Module withstand voltageThe total positive and total negative of the module to the electrical clearance of the housing

The above is the preliminary design of the battery system. Note that the BMS design is not included in this design.

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Battery Process:

  • Boutique | Cathode ingredients for lithium batteries
  • Boutique | Negative electrode ingredients and coating for lithium batteries
  • Boutique | Roller and slitting of lithium battery
  • Boutique | Cathode Coating
  • Boutique | Lithium battery into the shell and rolling groove
  • Boutique | Lithium battery cell baking, liquid injection and super welding cap
  • Boutique | Sealing and cleaning of lithium batteries
  • Boutique | Formation and capacity distribution of lithium batteries

Battery Design:

  • Design of Soft Wrapped Winding Battery – Electrochemical Design
  • Design of Soft Wrapped Winding Battery – Structural Design
  • [Dry goods] Lithium button battery assembly and test

Design Theory:

  • Theoretical Calculation of Lithium Battery Slurry Sedimentation
  • Lithium battery pole piece design theory
  • [Dry goods] Theoretical formula for the design of lithium battery tabs
  • The working principle of the battery cap [Part 1]
  • The working principle of the battery cap [Part 2]
  • Influence of physical and chemical parameters of lithium iron phosphate battery raw materials on electrical properties (1)
  • Influence of physical and chemical parameters of lithium iron phosphate battery raw materials on electrical properties (2)

Battery Material Testing and Evaluation Standards:

  • Test methods and standards for cathode materials (continued)
  • Test methods and standards for negative electrode materials
  • Test methods and standards for diaphragm materials
  • [Dry goods] Test method for HF (hydrofluoric acid) in electrolyte
  • Test methods and standards for NMP
  • Test methods and standards for electrolyte materials
  • Test methods and standards for KS-6
  • Test methods and standards for water-based adhesives
  • Test methods and standards for Super-P
  • Test methods and standards for aluminium foil
  • Test methods and standards for copper foil
  • [Dry goods] Electrolyte moisture test method
  • Test methods and standards for CMC
  • [Popularity] Contents of battery electrical performance test
  • [Popularity] Battery safety performance test project
Conclusion

When designing a battery bank for a specific location, a good design will ensure that the battery bank is perfectly: sized so the energy capacity matches the load requirements. sized for maximum and minimum voltage requirements for the desired application.

More Articles:

Introduction to Cell Balancing System,
Lithium ion battery fire accidents occur frequently, what is the reason?,
Analysis and summary of lithium battery,
IEC Battery Safety Standard for Power Batteries,
POWER BATTERY SHELL WATERPROOF DESIGN,
Production problems of lithium batteries,

Aging Mechanisms of Li-ion Batteries.

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