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US-20260128378-A1 - Fire Resistant Electrolyte for Lithium Batteries

US20260128378A1US 20260128378 A1US20260128378 A1US 20260128378A1US-20260128378-A1

Abstract

A mixture of bis-(2-methoxyethyl) carbonate (BMC) in a relatively low ratio with the cyclic carbonate EC as the electrolyte solvent in combination with a conductive lithium salt provides the desired electrolyte fire resistance to the resulting electrolyte while maintaining the desired electrolyte conductivity and electrolyte freezing point. The relatively low ratio of BMC to EC used to form the electrolyte solvent is 1:1.5 to 1:19, preferably 1:5.3 to 1:19, and more preferably 1:9 to 1:19, hence 40% to 5%, preferably 19% to 5%, and more preferably 10% to 5%, by weight of BMC to EC. The electrolyte solvent includes a 0.7 to 1.2 Molar, preferably a 0.8 to 1.1 Molar concentration of a lithium hexafluorophosphate salt to form the electrolyte.

Inventors

  • William Novis Smith

Assignees

  • American Hyperform, Inc.

Dates

Publication Date
20260507
Application Date
20241106

Claims (20)

  1. 1 . A fire-resistant electrolyte for a lithium battery, the electrolyte comprising: a conductive lithium salt chosen from lithium hexafluorophosphate, lithium bis-fluorosulfonyl imide, and combinations thereof; ethylene carbonate (EC); and bis-(2-methoxyethyl) carbonate (BMC), where the BMC and the EC are in a low weight ratio from 1:5.3 to 1:19, where the electrolyte has an electrical conductivity of at least 5 mS/cm at room temperature and pressure (RTP), and where the electrolyte has a boiling point of greater than 200 degrees Celsius at atmospheric pressure.
  2. 2 . The electrolyte of claim 1 , where the electrolyte has a closed cup flash point greater than 105 degrees Celsius at RTP.
  3. 3 . The electrolyte of claim 2 , where the electrolyte has a boiling point of at least 226 degrees Celsius at RTP.
  4. 4 . The electrolyte of claim 2 , where the electrolyte has a closed cup flash point greater than 120 degrees Celsius at RTP.
  5. 5 . The electrolyte of claim 2 , where the electrolyte has a closed cup flash point from 125 to 145 degrees Celsius at RTP.
  6. 6 . The electrolyte of claim 1 , where the electrolyte has a conductivity of at least 6.5 mS/cm.
  7. 7 . (canceled)
  8. 8 . The electrolyte of claim 1 , where the low weight ratio is from 1:9 to 1:19.
  9. 9 . The electrolyte of claim 1 , where the lithium hexafluorophosphate is present in the electrolyte at a 0.7 to 1.2 Molar concentration.
  10. 10 . The electrolyte of claim 1 , where the lithium hexafluorophosphate is present in the electrolyte at a 0.8 to 1.1 Molar concentration.
  11. 11 . The electrolyte of claim 1 , further comprising a second conductive lithium salt present in the electrolyte at up to a 0.6 Molar concentration.
  12. 12 . The electrolyte of claim 11 , where the second conductive lithium salt is chosen from lithium bis-fluorosulfonyl imide, lithium bis-trifluoromethyl sulfonate imide, lithium perchlorate, lithium trifluoromethyl sulfonate, and lithium tetrafluoroborate.
  13. 13 . The electrolyte of claim 1 , where the electrolyte is substantially free of a volatile electrolyte solvent.
  14. 14 . A fire-resistant electrolyte for a lithium battery, the electrolyte consisting essentially of: a conductive lithium salt comprising lithium hexafluorophosphate; ethylene carbonate (EC); and bis-(2-methoxyethyl) carbonate (BMC), where the BMC and the EC are in a low weight ratio from 1:1.5 to 1:19, the electrolyte has an electrical conductivity of at least 5 mS/cm at room temperature and pressure (RTP), and the electrolyte has a boiling point of greater than 200 degrees Celsius at atmospheric pressure.
  15. 15 . The electrolyte of claim 14 , where the low weight ratio is from 1:5.3 to 1:19.
  16. 16 . The electrolyte of claim 14 , where the low weight ratio is from 1:9 to 1:19.
  17. 17 . The electrolyte of claim 14 , where the lithium hexafluorophosphate is present in the electrolyte at a 0.7 to 1.2 Molar concentration.
  18. 18 . The electrolyte of claim 14 , where the lithium hexafluorophosphate is present in the electrolyte at a 0.8 to 1.1 Molar concentration.
  19. 19 . The electrolyte of claim 14 , further comprising a second conductive lithium salt present in the electrolyte at up to a 0.6 Molar concentration.
  20. 20 . The electrolyte of claim 19 , where the second conductive lithium salt is chosen from lithium bis-fluorosulfonyl imide, lithium bis-trifluoromethyl sulfonate imide, lithium perchlorate, lithium trifluoromethyl sulfonate, and lithium tetrafluoroborate.

Description

BACKGROUND Lithium batteries are used in all major applications for rechargeable and many non-rechargeable battery applications including automotive vehicles, mobile electronic devices, uninterruptable power supplies, robotic devices, and others. A rechargeable lithium-ion battery depends on a cathode (positive electrode), an anode (negative electrode), and an electrolyte that transfers ions between the cathode and anode. The cathode generally includes a lithium metal oxide coated onto a metal foil. The anode may contain graphite or silicon coated on a metal foil, generally a copper metal foil, or a lithium metal foil layered or otherwise coated on a substrate, where the substrate is often a metal foil made from copper. The high flammability of the organic electrolytes conventionally used in lithium batteries is the primary source of the fires reported in association with the failure or physical damage of lithium batteries. Such fires can be especially catastrophic when the lithium batteries are used in the transportation industry, such as in aircraft and automobiles, and when used as a portable power supply for handheld or backpack type electronic devices used in personal, business, and military applications. During such failure, which may arise from an electrical short, physical rupture of the external case, or other events resulting in a rapid internal temperature increase (exothermic runaway) of the battery, it is the flammable and volatile solvent or solvents used to form the electrolyte that produces the initial fire, and if not already ruptured, ruptures the external case due to the rapid expansion of the volatile solvent/s. Conventionally used electrolyte solvents are volatile and flammable, thus having boiling points at and below 100 degrees Celsius at atmospheric pressure and closed cup flash points around 25 degrees Celsius at atmospheric pressure. The boiling point of the electrolyte is important to the fire resistance of the battery because in an exothermic runaway condition the temperature inside the external case can reach a temperature of 200 degrees Celsius. The external case, generally made from a hard plastic or metal material, holds the individual battery cell or cells forming the battery. Electrolytes having a boiling point greater than 200 degrees Celsius at atmospheric pressure subjected to exothermic runaway within the external case of the battery generate significantly less vapor pressure inside the external case and are thus less likely to rupture the case. In addition to reducing the likelihood of external case rupture in response to exothermic runaway, the likelihood of “flash over”, the ignition of additional cells within the external case resulting in fire and catastrophic failure of the battery unit, also is reduced. Additionally, in the circumstance of external case rupture without exothermic runaway, such as from physical impact, the higher the boiling point and closed cup flash point of the electrolyte, the less likely the electrolyte is to ignite from direct ignition by external sources. To provide the desired electrolyte fire resistance, the solvent or solvent combination used to form the electrolyte should have a boiling point greater than 200 degrees Celsius and a closed cup flash point greater than 105 degrees Celsius, preferably greater than 120 degrees Celsius, at atmospheric pressure. Boiling point and the respective closed cup flash point temperatures of the electrolyte determine the temperature at which the cell separator/s that separate individual battery cell/s within the external case of the battery distort or break, resulting in shorting of the individual battery cells. However, while maintaining the desired electrolyte fire resistance a lithium battery electrolyte should also have a conductivity of at least 5 mS/cm, preferably of at least 6.5 mS/cm, to provide a desired electrolyte conductivity and thus battery discharge/recharge performance to the lithium battery. Without this desired conductivity, the electrolyte will result in a battery providing poor power delivery and slow recharge ability. A battery electrolyte should also have a desired electrolyte freezing point of at most +20 degrees Celsius at atmospheric pressure. The freezing point of the electrolyte is important, as if the electrolyte of the battery freezes, the conductivity of the electrolyte will go to zero, rendering the battery useless until self-heating occurs from attempted use and the electrolyte melts. Conventional attempts to make lithium batteries more fire resistant have generally focused on the addition of organic phosphates, heterocyclic nitrogen compounds, or fluorinated solvents to the conventionally used volatile electrolyte solvents. Other such attempts have focused on reducing the volatility of the conventionally used volatile electrolyte solvents by increasing their viscosity through the addition of gelling agents. Unfortunately, these conventional methods of increasing the fir