Method for adding additives that improve the cathode-electrolyte interface to improve the cycling stability of cathode electrodes

Abstract

A method for manufacturing a cathode electrode for a battery cell comprises mixing a cathode active material, a conductive filler, a binder, a solvent and a cathode-electrolyte interface (CEI) improving additive to form a slurry mixture; and pouring the slurry mixture onto a cathode current collector to form a cathode active material layer of a cathode electrode.

Description

INTRODUCTION

[0001] The information contained in this section is intended to provide a general context for the disclosure. Work by the presently named inventors, to the extent described in this introduction, as well as aspects of the description that may not otherwise be considered prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against this disclosure.

[0002] The present disclosure relates to cathode electrodes for battery cells and, more particularly, to methods for adding cathode-electrolyte interface improving additives to cathode electrodes during manufacture of the cathode electrode to improve cycling stability.

[0003] The present disclosure relates to battery cells and, more particularly, to battery cells having cathode electrodes comprising lithium- and manganese-rich cathode active material and a fluorinated electrolyte.

[0004] Electric vehicles (EVs), such as battery electric vehicles (BEVs), hybrid vehicles, and / or fuel cell vehicles, comprise one or more electric machines and a battery system with one or more battery cells, modules, and / or battery packs. A power control system is used to control the charging and / or discharging of the battery system during charging and / or driving.

[0005] Battery cells comprise cathode electrodes, anode electrodes, and separators. The cathode electrodes comprise a cathode active material layer disposed on a cathode current collector. The anode electrodes comprise an anode active material layer disposed on an anode current collector. SUMMARY

[0006] A method for manufacturing a cathode electrode for a battery cell comprises mixing a cathode active material, a conductive filler, a binder, a solvent, and a cathode-electrolyte interface (CEI) improving additive to form a slurry mixture; and pouring the slurry mixture onto a cathode current collector to form a cathode active material layer of a cathode electrode.

[0007] In some examples, the CEI-enhancing additive is selected from a group consisting of lithium difluorophosphate (LiPO2F2), lithium hexafluorophosphate (LiPF6), lithium fluoride (LiF), lithium phosphate (Li3PO4), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorosulfimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and combinations thereof.

[0008] In some examples, the CEI-enhancing additive includes lithium difluorophosphate (LiPO2F2).

[0009] In some examples, the method includes drying the cathode electrode in an oven; calendering the cathode electrode; arranging the cathode electrode in a stack; arranging the stack in a battery cell casing; and adding electrolyte to the battery cell casing.

[0010] In some examples, the electrolyte comprises a carbonate-based electrolyte. The electrolyte comprises a mixture of FEC and DEC. The electrolyte further comprises the CEI-enhancing electrolyte.

[0011] In some examples, the cathode active material is selected from a group consisting of lithium- and manganese-rich cathode material (LMR), lithium nickel-cobalt-manganese-aluminum (NCMA), lithium nickel-manganese-cobalt (NMC), lithium manganese oxide (LMO), lithium nickel oxide (LNO), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and combinations thereof. The CEI-enhancing additive comprises 0.25 wt% to 5 wt%, and the cathode active material comprises 95 wt% to 99.75 wt%. The CEI-enhancing additive comprises 0.25 wt% to 2 wt%, and the cathode active material comprises 98 wt% to 99.75 wt%.

[0012] A method for manufacturing a cathode electrode for a battery cell includes mixing a cathode active material, a conductive filler, a binder, and a solvent to form a slurry mixture; pouring the slurry mixture onto a cathode current collector to form a cathode active material layer of the cathode electrode; and one of ball milling and spray-dry coating a cathode-electrolyte interface (CEI) improving additive onto the cathode active material layer.

[0013] For other features, the CEI-enhancing additive is selected from the group consisting of lithium difluorophosphate (LiPO2F2), lithium hexafluorophosphate (LiPF6), lithium fluoride (LiF), lithium phosphate (Li3PO4), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorosulfimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and combinations thereof. The cathode active material is selected from the group consisting of lithium and manganese-rich cathode material (LMR), lithium nickel cobalt manganese aluminum (NCMA), lithium nickel manganese cobalt (NMC), lithium manganese oxide (LMO), lithium nickel oxide (LNO), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and combinations thereof.

[0014] In other features, the method includes drying the cathode electrode in an oven; calendering the cathode electrode; arranging the cathode electrode in a stack; arranging the stack in a battery cell casing; and adding electrolyte to the battery cell casing.

[0015] For other features, the electrolyte also includes the CEI-enhancing electrolyte. The CEI-enhancing additive comprises 0.25 wt% to 5 wt%, and the cathode active material comprises 95 wt% to 99.75 wt%.

[0016] A method for manufacturing a cathode electrode for a battery cell comprises mixing a cathode active material, a conductive filler, a binder, and a solvent to form a slurry mixture; pouring the slurry mixture onto a cathode current collector to form a cathode active material layer of the cathode electrode; drying the cathode electrode in an oven; calendering the cathode electrode; and immersing the cathode electrode in a bath comprising a cathode-electrolyte interface (CEI) improving additive and a solvent.

[0017] For other features, the CEI-enhancing additive is selected from the group consisting of lithium difluorophosphate (LiPO2F2), lithium hexafluorophosphate (LiPF6), lithium fluoride (LiF), lithium phosphate (Li3PO4), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorosulfimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and combinations thereof. The cathode active material is selected from the group consisting of lithium and manganese-rich cathode material (LMR), lithium nickel cobalt manganese aluminum (NCMA), lithium nickel manganese cobalt (NMC), lithium manganese oxide (LMO), lithium nickel oxide (LNO), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and combinations thereof.

[0018] In other features, the method comprises arranging the cathode electrode in a stack; arranging the stack in a battery cell casing; and adding electrolyte to the battery cell casing. The electrolyte also includes the CEI-enhancing electrolyte. The CEI-enhancing additive comprises 0.25 wt% to 5 wt%, and the cathode active material comprises 95 wt% to 99.75 wt%.

[0019] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims, and drawings. The detailed description and specific examples are for illustrative purposes only and are not intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present disclosure will be more fully understood from the detailed description and the accompanying drawings, in which: Fig. 1 is a side cross-sectional view of an example of a battery cell including cathode electrodes, anode electrodes, and separators according to the present disclosure; Fig. 2 is a side cross-sectional view of an example of a cathode electrode comprising a CEI-enhancing additive according to the present disclosure; Fig. 3 is a flow diagram of an example of a method for making cathode electrodes using a slurry mixture comprising a cathode-electrolyte interface improving additive according to the present disclosure; Fig. 4 is a flow diagram of an example of a method for manufacturing cathode electrodes comprising applying a cathode-electrolyte interface improving additive to a cathode active material layer by ball milling or spray dry coating according to the present disclosure; Fig. 5 is a flow diagram of an example method for immersing a cathode electrode in a bath comprising a cathode-electrolyte interface improving additive according to the present disclosure; Fig. 6 and Fig. 7 are graphs illustrating the percentage retention of discharge capacity and discharge capacity as a function of cycles, respectively, for various concentrations of the CEI-enhancing additive added to a slurry mixture according to the present disclosure; and Fig. 8 is a graph illustrating discharge capacity and percent discharge capacity retention, respectively, as a function of cycles for a first battery cell comprising a CEI-enhancing additive added to the electrolyte and a second battery cell comprising a CEI-enhancing additive added to the slurry in accordance with the present disclosure.

[0021] Reference symbols may be reused in the drawings to identify similar and / or identical elements. DETAILED DESCRIPTION

[0022] Although battery cells according to the present disclosure are shown in connection with electric vehicles, the battery cells may also be used in stationary applications and / or other applications.

[0023] During battery cell manufacturing, some cathode-electrolyte interface (CEI) problems can be mitigated by creating artificial barriers or coatings on the cathode active material particles. In some battery cells, the formation of stable cathode-electrolyte interfaces (CEI) is facilitated by adding CEI-enhancing additives to the electrolyte after battery cell manufacturing. The CEI-enhancing additive, mixed with the electrolyte, forms the coating on the cathode active material. The coating can, for example, comprise the species lithium fluoride (LiF) and / or lithium phosphate (Li3PO4).

[0024] In some examples, a precursor such as lithium difluorophosphate (LiPO2F2) is added to the electrolyte to form the coating of the cathode active material with LiF and Li3PO4. The limited solubility of the CEI-enhancing additives (e.g., LiPO2F2) in some electrolyte systems (e.g., carbonate-based electrolytes, fluoroethylene carbonate (FEC):diethyl carbonate (DEC) solvent systems) presents a challenge. For example, adding the CEI-enhancing additive to FEC:DEC solvent systems produces concentrations of up to about 1 wt.% of the cathode active material layer. However, higher concentrations are desirable. Adding more CEI-enhancing additive to the electrolyte does not increase the concentration of the CEI-enhancing additive on the cathode active material or improve the stability of the CEI.

[0025] The present disclosure relates to methods for adding the CEI-enhancing additive to the cathode active material layer during manufacturing as a replacement for or in addition to adding the CEI-enhancing additive to the electrolyte. In some examples, the method for manufacturing the cathode electrode according to the present disclosure includes adding the CEI-enhancing additive (e.g., LiPO2F2) to a slurry mixture for a cathode active material layer during the manufacturing process. Applying this approach promotes the formation of a robust CEI, thereby improving the stability and performance of the CEI. In some examples, the CEI-enhancing additive is also added to the electrolyte.

[0026] In other examples, the CEI-enhancing additive is applied to the cathode active material layer during manufacturing by ball milling or spray coating. In further examples, the cathode electrode is manufactured without the CEI-enhancing additive and calendered. The electrode is then immersed in a bath comprising a mixture of the CEI-enhancing additive and solvent to coat the cathode electrode. The cathode electrode is dried in an oven to remove the solvent. In some examples, the process can also be performed in addition to other additives added to the electrolyte.

[0027] With reference now to Fig. 1, a battery cell 10 includes C cathode electrodes 20, A anode electrodes 40, and S separators 32 arranged in a predetermined order within a battery cell stack 12, where C, S, and A are integers greater than zero. The battery cell stack 12 is disposed within a housing 50. The electrolyte 52 is added to the housing 50 as described further below. In some examples, the electrolyte optionally includes the CEI-enhancing additive and / or other additives. The C cathode electrodes 20-1, 20-2, ..., and 20-C include cathode active material layers 24 disposed on one or both sides of a cathode current collector 26.

[0028] During charging / discharging, the A-anode electrodes 40 and the C-cathode electrodes 20 exchange lithium ions. The A-anode electrodes 40-1, 40-2, ..., and 40-A include anode active material layers 42 disposed on one or both sides of the anode current collectors 46. In some examples, the cathode active material layers 24 and / or the anode active material layers 42 include coatings comprising one or more active materials, one or more conductive additives, and / or one or more binder materials applied to the current collectors.

[0029] In some examples, the cathode current collector 26 and / or the anode current collector 46 comprise a metal foil, a metal mesh, perforated metal, three-dimensional (3D) metal foam, and / or expanded metal. In some examples, the current collectors are made of one or more materials selected from a group consisting of copper, stainless steel, brass, bronze, zinc, aluminum, and / or their alloys. The outer tabs 28 and 48 are connected to the current collectors of the cathode electrodes and anode electrodes, respectively, and can be arranged on the same or different sides of the battery cell stack 12. The outer tabs 28 and 48 are connected to the terminals of the battery cells.

[0030] With reference now to Fig. 2, one of the C cathode electrodes 20 is shown in more detail. The cathode active material layer 24 of the C cathode electrodes 20 comprises a cathode active material 62, a conductive additive 64, and a binder 66.

[0031] As described above, the CEI-enhancing additive can be added to the slurry forming the cathode active material layer 24 (e.g., as shown at 68), applied to the cathode electrode by ball milling or spray-dry coating, or the cathode electrode can be immersed in a mixture of the CEI-enhancing additive and solvent. In some examples, the CEI-enhancing additive is selected from a group consisting of lithium difluorophosphate (LiPO2F2), lithium hexafluorophosphate (LiPF6), lithium fluoride (LiF), lithium phosphate (Li3PO4), lithium difluoro(o-xalato)borate (LiDFOB), lithium difluorosulfimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and combinations thereof.

[0032] In some examples, the cathode active material is selected from a group consisting of lithium and manganese rich cathode material (LMR), lithium nickel cobalt manganese aluminum (NCMA), lithium nickel manganese cobalt (NMC), lithium manganese oxide (LMO), lithium nickel oxide (LNO), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and combinations thereof.

[0033] In some examples, the CEI-enhancing additive comprises 0.25 wt.% to 5.0 wt.% of the cathode active material. In some examples, the CEI-enhancing additive comprises 0.25 wt.% to 2.0 wt.% of the cathode active material. In some examples, the CEI-enhancing additive comprises 1.0 wt.% to 2.0 wt.% of the cathode active material. In some examples, the CEI-enhancing additive is added during manufacturing and to the electrolyte (e.g., 0 to 1.0 wt.% CEI-enhancing additive).

[0034] In some examples, the CEI-enhancing additive is added directly to the slurry comprising the cathode active material, the conductive filler, the binder, and the solvent (e.g., NMP). In other examples, the cathode electrode is poured onto the current collector, and then the CEI-enhancing additive is ball-milled or dry-sprayed onto the cathode active material layer. In some examples, the cathode electrodes are fabricated and then immersed in a bath comprising a CEI-enhancing additive and a solvent (such as LiPO2F2). The cathode electrodes are dried in an oven to evaporate the solvent.

[0035] With reference now to Fig. 3, a method for producing cathode electrodes comprises adding one or more CEI-enhancing additives to a slurry mixture and pouring the casting onto a cathode current collector. At 150, a cathode active material, a conductive filler, a binder, and a solvent are mixed to form a slurry mixture. The one or more CEI-enhancing additives are added to the slurry mixture. At 154, the slurry mixture is poured onto a cathode current collector. At 158, the cathode electrodes are dried in an oven to remove the solvent.

[0036] At 160, the cathode electrodes are calendered using one or more pairs of rollers that press and / or heat the cathode electrodes. Additional processing occurs (e.g., cutting or punching individual cathode electrodes, forming external tabs, etc.). At 162, the cathode electrodes, anode electrodes, and separators are arranged in a stack, bonded together, and / or disposed within a battery cell casing. At 164, the liquid electrolyte is added to the battery cell. In some examples, the electrolyte optionally also includes the CEI-enhancing additive to supplement the CEI-enhancing additive added in step 150.

[0037] With reference now to Fig. 4, a method for producing cathode electrodes includes ball milling or spray-dry coating the CEI-enhancing additive onto the cathode electrode. At 200, a cathode active material, a conductive filler, a binder, and a solvent are mixed into a slurry mixture. At 204, the slurry mixture is poured onto a cathode current collector. At 208, one or more CEI-enhancing additives are applied to the cathode active material layer by ball milling or spray-dry coating.

[0038] At 212, the cathode electrodes are dried in an oven to remove the solvent. At 216, the cathode electrodes are calendered using one or more pairs of rollers that press and / or heat the cathode electrodes. Additional processing occurs (e.g., cutting or punching individual cathode electrodes, forming external tabs, etc.). At 220, the cathode electrodes, anode electrodes, and separators are arranged in a stack, bonded together, and disposed within a battery cell casing. At 224, the liquid electrolyte is added to the battery cell. In some examples, the electrolyte also optionally includes the CEI-enhancing additive to supplement the CEI-enhancing additive added in step 208.

[0039] With reference now to Fig. 5, a method for preparing cathode electrodes includes immersing the cathode electrodes in a bath comprising one or more cathode-electrolyte interface-enhancing additives and a solvent. At 250, a cathode active material, a conductive filler, a binder, and a solvent are mixed into a slurry mixture. At 254, the slurry mixture is poured onto a cathode current collector. At 260, the cathode electrode is immersed in a bath comprising one or more CEI-enhancing additives and the solvent. At 264, the cathode electrodes are dried in an oven to remove the solvent. At 268, the cathode electrodes are calendered using one or more pairs of rollers that press and / or heat the cathode electrodes. Additional processing is carried out (e.g. cutting or punching individual cathode electrodes, forming external tabs, etc.).At 272, the cathode electrodes, anode electrodes, and separators are stacked, bonded together, and arranged in a battery cell housing. At 274, the liquid electrolyte is added to the battery cell. In some examples, the electrolyte also optionally includes the CEI-enhancing additive to supplement the CEI-enhancing additive added in step 270.

[0040] Methods for adding CEI-enhancing additives during manufacturing, instead of or in addition to adding the CEI-enhancing additive to the electrolyte, can be used to optimize the CEI to improve cycling stability with little or no loss of capacity. The amount of CEI-enhancing additive added is not limited by its solubility in the electrolyte-solvent system. The methods described herein achieve uniform distribution of the additives throughout the cathode active material layer by adding the CEI-enhancing additive during cathode electrode manufacturing.

[0041] With reference now to Fig. 6 and Fig. Figure 7 shows the percentage retention of discharge capacity and the discharge capacity as a function of cycles for different concentrations of the CEI-enhancing additive. In this example, button battery cells comprised cathode active material that included lithium- and manganese-rich (LMR) cathode active material with a porosity of 30%. The anode comprised 5.5 wt.% SiO x / graphite and a porosity of 30%. The electrolyte contains 50µl FEC:DEC in a ratio of 1:4. The button battery cell has a positive capacity of ∼ 5 mAh / cm 2 and a negative capacity of ∼ 5.5 mAh / cm 2 The active mass on the cathode electrode was 20-21 mg / cm 2The battery cells were subjected to formation and a life cycle protocol. Formation was performed for two cycles of continuous current charging (CCC) at C / 20 to 4.6 V and continuous voltage charging (CVC) at 4.6 V to C / 50. The life cycle protocol included CCC charging at C / 3 to 4.6 V, CVC at 4.6 V to C / 20, and continuous current discharging (CC) at C / 3 to 2.0 V. In this example, 2 wt% LiP-2F2 provided a higher percentage of discharge capacity retention over a higher number of cycles.

[0042] With reference now to Fig. 8 are the discharge capacity and the percentage retention of discharge capacity as a function of cycles for the button battery cells in the Fig. 6 and Fig.7. The graph compares the discharge capacity at 306 and the percentage retention of discharge capacity at 308 for a first battery cell (including the LMR active material DECO1 and 1 wt% LiPO2F2 added to the electrolyte) and a second battery cell (including the LMR active material and 2 wt% LiPO2F2 with the DECO1 added to the slurry).

[0043] The discharge capacity and percentage retention of discharge capacity for the first battery cell are shown at 310 and 320, respectively. The discharge capacity and percentage retention of discharge capacity for the second battery cell are shown at 314 and 324, respectively. The addition of LiPO2F2 to either the slurry mixture or the electrolyte shows similar capacity and cycling performance. Therefore, slurry addition can be used as a method for producing battery cells with an optimal amount of CEI-enhancing additive (e.g., LiPO2F2).

[0044] The above description is merely illustrative and is not intended to limit the disclosure, its application, or uses in any way. The broad teachings of the disclosure may be embodied in a variety of forms. Therefore, while this disclosure includes specific examples, the true scope of the disclosure should not be limited thereto, since other changes will become apparent after studying the drawings, the patent specification, and the following claims. It is understood that one or more steps within a method may be performed in different orders (or simultaneously) without altering the principles of the present disclosure.Furthermore, although the embodiments are each described above as having specific features, each one or more of these features described with respect to one embodiment of the disclosure may be implemented and / or combined with features of any of the other embodiments, even if this combination is not expressly described. In other words, the described embodiments are not mutually exclusive, and an exchange of one or more embodiments for one another remains within the scope of this disclosure.

[0045] Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including "connected," "engaging," "coupled," "adjacent," "beside," "on top of," "over," "below," and "disposed." If a relationship between first and second elements is not explicitly described as "direct" in the above disclosure, that relationship may be a direct relationship, with no other intervening elements between the first and second elements, or an indirect relationship, with one or more intervening elements (either spatial or functional) between the first and second elements.As used herein, the term "A, B and / or C" should be construed as logical (A ORed with B ORed with C) using a non-exclusive logical OR, and not as "at least one of A, at least one of B and at least one of C".

[0046] In the figures, the direction of an arrow, as indicated by the arrowhead, generally illustrates the flow of information (e.g., data or instructions) of interest to the illustration. For example, if element A and element B exchange a lot of information, but the information passed from element A to element B is relevant to the illustration, the arrow may point from element A to element B. This unidirectional arrow does not imply that no other information is passed from element B to element A. Furthermore, for information being sent from element A to element B, element B may send requests for or acknowledgments of receipt of the information to element A.

Claims

[1] A method for producing a cathode electrode for a battery cell, comprising: Mixing a cathode active material, a conductive filler, a binder, a solvent, and a cathode-electrolyte interface (CEI) improving additive to form a slurry mixture; and Pouring the slurry mixture onto a cathode current collector to form a cathode active material layer of a cathode electrode. [2] The method of claim 1, wherein the CEI-enhancing additive is selected from a group consisting of lithium difluorophosphate (LiPO2F2), lithium hexafluorophosphate (LiPF6), lithium fluoride (LiF), lithium phosphate (Li3PO4), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorosulfimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and combinations thereof. [3] The method of claim 1, wherein the CEI-enhancing additive comprises lithium difluorophosphate (LiPO2F2). [4] The method of claim 1, further comprising: Drying the cathode electrode in an oven; Calendering the cathode electrode; Arranging the cathode electrode in a stack; Arranging the stack in a battery cell housing; and Adding electrolyte to the battery cell casing. [5] The method of claim 4, wherein the electrolyte comprises a carbonate-based electrolyte. [6] The method of claim 4, wherein the electrolyte comprises a mixture of FEC and DEC. [7] The method of claim 4, wherein the electrolyte further comprises the CEI-enhancing additive. [8] The method of claim 1, wherein the cathode active material is selected from a group consisting of lithium and manganese rich cathode material (LMR), lithium nickel cobalt manganese aluminum (NCMA), lithium nickel manganese cobalt (NMC), lithium manganese oxide (LMO), lithium nickel oxide (LNO), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP) and combinations thereof. [9] The method of claim 1, wherein the CEI-enhancing additive comprises 0.25 wt% to 5 wt% and the cathode active material comprises 95 wt% to 99.75 wt%. [10] The process of claim 1, wherein the CEI-enhancing additive comprises 0.25 wt% to 2 wt% and the cathode active material comprises 98 wt% to 99.75 wt%.

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