This application claims the priority benefit of Taiwan application no. 101149627, filed on Dec. 24, 2012. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
The technical field relates to a lithium ion battery and an electrode structure thereof.
A positive temperature coefficient (PTC) refers to materials or devices with very large PTCs, usually referred to as PTC thermistors, and are also referred to as resettable fuses. The PTC materials are divided into PPTC (polymer positive temperature coefficient) material and CPTC (ceramic positive temperature coefficient) material. The researched PPTC material is applied in the design of the exterior of the battery module, and the composition of PPTC material includes PE (polyethylene) polymer and conductive particles. Under normal conditions (low temperature), the conductive particles form a chained conductive channel in the polymer matrix material that in turn forms a conductive passage, where the device is in a state of low resistivity. When an over-current occurs in the circuit (e.g. a short circuit), the heat generated by the large current may melt the polymer crystals, interrupting the originally chained conductive channel. As a result, the device changes from low resistivity to high resistivity and blocks the circuit.
The design of the exterior PTC applied in lithium ion batteries may only prevent overcharging, and may not protect the battery with real time sensing when temperature of the interior of the battery rises, due to the design of the exterior PTC not being thermo-sensitive. Although the PTC in the electrode coating layer may improve the problems above, a design with only one step of blocking the electronic channel may only directly block the electronic channel when the battery temperature rises.
The disclosure provides an electrode structure for a lithium ion battery. The electrode structure includes a current collecting substrate, an electrode active material layer on the current collecting substrate, and a complex thermo-sensitive coating layer sandwiched in between the current collecting substrate and the electrode active material layer. The complex thermo-sensitive coating layer at least contains two or more of PTC (positive temperature coefficient) materials so as to have adjustable stepped resistivity according to temperature rise.
The disclosure also provides a lithium ion battery. The lithium ion battery at least includes an electrolyte solution and an electrode group, wherein the electrode group includes a cathode, an anode, and a separator between the cathode and the anode, and is characterized in that at least one of the cathode and the anode is the aforementioned electrode structure for the lithium ion battery.
Several exemplary embodiments accompanied with figures are described in detail below to further describe the disclosure in details.
The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments and, together with the description, serve to explain the principles of the disclosure.
Referring to
The “adjustable stepped resistivity according to temperature rise” in the disclosure refers to the stepwise resistivity change (at least two steps) with the increase of temperature, as shown in
The polymer melting temperature of the PTC materials of the complex thermo-sensitive coating layer 104 is, for instance, between 70° C. and 160° C., preferably between 80° C. and 130° C. The ceramic Curie temperature of the PTC materials of the complex thermo-sensitive coating layer 104 is, for instance, between 60° C. and 120° C.
Continuing with
In the present embodiment, the aforementioned CPTC material may be doped-BaTiO3, wherein the dopant elements of the doped-BaTiO3 are selected from the group consisting of Cr, Pb, Ca, Sr, Ce, Mn, La, Y, Nb, Nd, Al, Cu, Si, Ta, Zr, Li, F, Mg, and lanthanide elements. Based on the total amount of the dopant elements, the content of Pb, Ca, Sr, or Si is 100 mol % or less, and the content of the other elements is 20 mol % or less. Moreover, when the PTC materials are all the CPTC material, polymer materials may be added to increase the adhesion. Moreover, when the PTC materials are all the CPTC material, conductive particles such as metal particles, metal oxides, or carbon black (termed as “first conductive particles” hereinafter) may also be added to improve the conductivity, wherein the carbon black is, for instance, conductive carbon (VGCF, Super P®, KS4®, KS6®, or ECP®), a nanoscale conductive carbon material, acetylene black or the like. The aforementioned first conductive particles usually account for 3 wt % to 5 wt % of the total amount of the complex thermo-sensitive coating layer 104, but the disclosure is not limited thereto. Moreover, the CPTC material and the first conductive particles account for, for instance, 20 wt % to 80 wt % of the total amount of the complex thermo-sensitive coating layer.
In the present embodiment, the polymer material in the PPTC material (provided the melting temperature of the polymer is between 70° C. and 160° C.) may be polyethylene (PE), polyvinylidene fluoride (PVDF), polypropylene (PP), polyvinyl acetate (PVA) or the like.
In the present embodiment, when the PTC materials are all the PPTC material, conductive particles in the aforementioned PPTC material (referred to as “second conductive particles” hereinafter) account for, for instance, 20 wt % to 80 wt % of the total amount of the complex thermo-sensitive coating layer. The aforementioned second conductive particles are, for instance, metal particles, metal oxides, or carbon black that improve the conductivity of the PPTC material. In particular, the carbon black is, for instance, conductive carbon (VGCF, Super P®, KS4®, KS6®, or ECP®), a nanoscale conductive carbon material, acetylene black or the like.
Moreover, if the PTC materials include both the PPTC material and the CPTC material, then the aforementioned CPTC material, first conductive particles, and second conductive particles account for, for instance, 20 wt % to 80 wt % of the total amount of the complex thermo-sensitive coating layer.
A plurality of experiments are listed below to demonstrate the efficacy of the disclosure.
First, 0.4 mol % of Nb doped Ba0.9Sr0.1TiO3 is mixed with polyethylene (PE) in a weight ratio of 8:2, 6:4, 5:5, or 2:8, and then 5 wt % of conductive particles (Super P®) are added. The mixture is evenly mixed and formed into a coating layer, and then the resistivity change of the coating layer according to temperature rise is measured. The result is shown in
It is known from
First, 0.4 mol % of Nb doped Ba0.9Sr0.1TiO3 is mixed with polyethylene (PE) in a weight ratio of 6:4, and then 5 wt % of conductive particles (Super P®) are added. The mixture is evenly mixed and formed into a coating layer, and then the resistivity change of the coating layer according to temperature rise is measured. The result is shown in
First, 0.4 mol % of Nb doped Ba0.9Sr0.1TiO3 is mixed with polyethylene (PE) in a weight ratio of 2:1, and then 10 wt % of conductive particles (Super P®) are added. The mixture is evenly mixed and formed into a coating layer, and then the resistivity change of the coating layer according to temperature rise is measured. The result is shown in
In
Based on the above, in the disclosure, the complex thermo-sensitive coating layer containing two or more of the PTCs is coated on the surface of the current collecting substrate so as to have adjustable stepped resistivity according to temperature rise. As a result, not only is the complex thermo-sensitive coating layer more sensitive in detecting the safety situation of the battery, but the complex thermo-sensitive coating layer is also able to control the current when over-temperature abnormality occurs locally in the interior of the battery. The probability of thermal runaway in the battery is thus significantly reduced.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.
Number | Date | Country | Kind |
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101149627 | Dec 2012 | TW | national |