INTRODUCTION

The present disclosure relates to vehicle battery cell charging and battery cell design, and in particular lithium-ion battery cell charging and lithium-ion battery design for electric powered vehicles.

Vehicle battery packs, particularly for lithium-based batteries, such as lithium-oxide batteries are susceptible to plating of metallic lithium (Li) during a battery charging process. Lithium plating occurs during fast charging of the battery pack and at low temperature environmental conditions when a temperature of the battery pack is below an optimum operating temperature range of approximately 25 to 35 degrees Centigrade. Lithium plating during charging is of particular concern when battery temperature is 10 degrees Centigrade or lower. Lithium plating is also of concern during battery fast charging operation, defined as charging in approximately 30 minutes or less. Lithium plating is particularly prevalent during fast charging operation and when the battery pack is at or below 10 degrees Centigrade. Plating of metallic lithium can induce lithium-ion (Li-ion) battery cell degradation or battery cell failure, which are a failure mechanism and an operating concern for an electric powered vehicle.

Methods to pre-heat the battery pack to avoid low temperature charging using heated air or fluid require additional components such as heating elements, pumps to induce flow and sensors. These systems have the potential to leak and create other failure events, and also add vehicle weight, negatively impact arrangement space, and increase cost.

Thus, while current lithium-ion battery designs achieve their intended purpose, there is a need for a new and improved system and method for allowing fast battery charging and charging at battery temperatures below 25 degrees Centigrade while mitigating lithium plating of individual lithium-ion battery cells.

SUMMARY

According to several aspects, a battery cell thermal conditioning system for a vehicle includes a battery pack having battery cells. A carbon nanotube sheet is positioned in proximity to one of the battery cells. A controller directs current flow to the carbon nanotube sheet when a temperature of the one of the battery cells drops below a predetermined threshold temperature.

In another aspect of the present disclosure, a power source independent of the battery pack provides the current flow upon command from the controller.

In another aspect of the present disclosure, the power source defines a 12 VDC battery or a 24 VDC battery.

In another aspect of the present disclosure, the carbon nanotube sheet includes: a positive terminal connected to a positive terminal of the power source; a negative terminal connected to a negative terminal of the power source; and a thickness of approximately 100 microns.

In another aspect of the present disclosure, the carbon nanotube sheet is positioned in direct contact with one of the battery cells and the controller directs the current flow to the carbon nanotube sheet until a temperature of the one of the battery cells increases to a minimum optimum temperature.

In another aspect of the present disclosure, the minimum optimum temperature is approximately 25 degrees Centigrade.

In another aspect of the present disclosure, a second carbon nanotube sheet is positioned in direct contact with a second one of the battery cells on a second side of the foam layer, the controller also directing the current flow to the second carbon nanotube sheet.

In another aspect of the present disclosure, the controller defines a pulse width modulated controller; and a voltage signal from the controller defines at least a 0% current flow, a 25% current flow and a 100% current flow.

In another aspect of the present disclosure, the 25% current flow is provided when the predetermined threshold temperature is at or above approximately 10 degrees Centigrade and below approximately 25 degrees Centigrade; and the 100% current flow is provided when the predetermined threshold temperature is below approximately zero degrees Centigrade.

In another aspect of the present disclosure, the carbon nanotube sheet is positioned at an inner wall of a housing which contains the battery pack, the carbon nanotube sheet when energized by the current flow producing radiant heat energy acting to heat the battery pack.

According to several aspects, a battery cell thermal conditioning system includes a battery pack having multiple battery cells. A foam layer is positioned between adjacent ones of the battery cells. A carbon nanotube sheet positioned in direct contact with one of the battery cells with the carbon nanotube sheet positioned on a first side of the foam layer. A controller directs current flow to the carbon nanotube sheet when a temperature of the one of the battery cells contacted by the carbon nanotube sheet drops below a predetermined threshold temperature.

In another aspect of the present disclosure, the controller directs the current flow to the carbon nanotube sheet until a temperature of the one of the battery cells increases to a minimum optimum temperature of approximately 25 degrees Centigrade.

In another aspect of the present disclosure, a second carbon nanotube sheet is positioned in direct contact with a second one of the battery cells on a second side of the foam layer, the controller also directing the current flow to the second carbon nanotube sheet.

In another aspect of the present disclosure, a battery control unit receives sensor signals from the battery pack and monitors a voltage of the battery pack. The power source defines a direct current battery independent of the battery pack providing the current flow upon command from the controller.

In another aspect of the present disclosure, the controller defines a pulse width modulated controller allowing current to the carbon nanotube sheet to be directly controlled within predetermined ranges and power levels to provide different heat-up rates for different temperature ranges of the battery pack.

In another aspect of the present disclosure, the foam layer is a polymeric material which is elastically compressible to allow thermal expansion and contraction of the battery cells and vibrational motion of the battery pack and the battery cells while mitigating against direct contact between any of the battery cells

In another aspect of the present disclosure, a determination is performed if an immediate high battery demand follows a period of non-operation of the vehicle when an ambient temperature is below an optimum operating temperature of the battery pack but has not dropped to the predetermined threshold temperature, demanding current flow be initiated to the carbon nanotube sheet.

According to several aspects, a battery cell thermal conditioning system for a vehicle includes a battery pack having multiple battery cells and multiple sensors including a temperature sensor and a voltage sensor identifying a temperature and a voltage of the battery pack. Multiple foam layers are individually positioned between first successive ones of the battery cells. A first carbon nanotube sheet is positioned in direct contact with one of the battery cells on a first side of the foam layers and a second carbon nanotube sheet is positioned in direct contact with a different one of the battery cells on a second side of the foam layers. A cooling plate is positioned between second successive ones of the battery cells. A controller directs current flow to the first carbon nanotube sheet and the second carbon nanotube sheet when a temperature indicated by a temperature signal from the temperature sensor of the one of the battery cells contacted by the first or the second carbon nanotube sheet drops below a predetermined threshold temperature.

In another aspect of the present disclosure, a battery charging rate is determined to identify if a fast charging operation is present. A battery pack temperature condition is determined using the sensors to identify if a predetermined low temperature threshold is met at which current flow is initiated to the first and the second carbon nanotube sheets.

In another aspect of the present disclosure, a first face of the first one of the battery cells directly abuts the cooling plate to provide conductive cooling of the first one of the battery cells. A second face of the first one of the battery cells is oppositely directed with respect to the first face of the first one of the battery cells and directly abuts the first carbon nanotube sheet. A first face of the second one of the battery cells directly abuts the cooling plate opposite to the first face of the first one of the battery cells to provide conductive cooling of the second one of the battery cells. A second face of the second one of the battery cells is oppositely directed with respect to the first face of the second one of the battery cells and directly abuts the second carbon nanotube sheet.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

