Lithium iron phosphate (LFP) electrode with improved processability

Abstract

The present invention relates to lithium iron phosphate (LFP) electrodes with improved processability. An electrode for a lithium ion battery includes an electrochemically active material comprising lithium, an electrically conductive material comprising carbon; and a binder material comprising a polymer having a molecular weight greater than 800 thousand Daltons or an acid-modified polyvinylidene fluoride.

Description

Technical Field

[0001] The present disclosure relates generally to lithium-ion batteries and, more particularly, to lithium iron phosphate (LFP) electrodes with improved processability for lithium-ion batteries. Background Art

[0002] The information provided in this section is for the purpose of generally introducing the background of the present disclosure. No admission is made, either explicitly or implicitly, that the work of the presently named inventors described in this section is prior art to the present disclosure, nor is it admitted that the work is prior art to the present disclosure with respect to the specification that may not have been otherwise identified as prior art at the time of filing.

[0003] Lithium-ion battery packs are widely used in various applications. For example, lithium-ion battery packs can be used to power computing devices such as laptop computers, handheld devices (e.g., smartphones and tablets), etc. Lithium-ion battery packs can also be used to power vehicles such as electric vehicles (EVs). Summary of the Invention

[0004] An electrode for a lithium-ion battery, comprising: an electrochemically active material comprising lithium, a conductive material comprising carbon; and a binder material comprising a polymer having a molecular weight greater than 800 kilodaltons or acid-modified polyvinylidene fluoride.

[0005] In other features, the electrode comprises 92-98.5 wt % electrochemically active material.

[0006] In other features, the electrode comprises 96-97.5 wt % electrochemically active material.

[0007] In other features, the electrode comprises 0.6-4 wt% conductive material.

[0008] In other features, the electrode comprises 0.8-2 wt% conductive material.

[0009] In other features, the electrode comprises 1-4 wt % binder material.

[0010] In other features, the electrode comprises 1.5-2.5 wt% binder material.

[0011] In other features, the electrochemically active material comprises a phosphate polyanion.

[0012] In other features, the electrochemically active material comprises a surface area greater than or equal to 6 m 2 / g of phosphate polyanion.

[0013] In other features, the electrochemically active material includes phospholipidite.

[0014] In other features, the electrochemically active material is selected from Li x MPO4, where M = Mn, Fe, Co and Ni.

[0015] In other features, the electrochemically active material is selected from LiMn x Fe y PO4, where x+y=1.

[0016] In other features, the electrochemically active material is selected from LiFe(P2O7), LiFe4(P2O7)3, LiV2(PO4)3, LiVOPO4, LiV2(PO4)3 and LiVPO4F.

[0017] In other features, the conductive material is selected from carbon black (CB), acetylene black (AB) carbon, furnace black (FB) carbon, graphene nanoplatelets (GNPs), carbon nanofibers (CNFs), graphene (G), graphene oxide (GO), reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs) and / or single-walled carbon nanotubes (SWCNTs), and blends thereof.

[0018] In other features, the conductive material includes acetylene black (AB) carbon and multi-walled carbon nanotubes (MWCNTs) or includes furnace black (FB) carbon and multi-walled carbon nanotubes (MWCNTs).

[0019] In other features, the electrode comprises 96.5-97.25 wt % electrochemically active material.

[0020] In other features, the electrode comprises 1.5-2.1 wt % binder material.

[0021] In other features, the polymer has a molecular weight greater than 800 kilodaltons and less than 1200 kilodaltons.

[0022] In other features, the polymer comprises acidic chemical functional groups along the polymer backbone, wherein the acid content is greater than 0.1 milliequivalents per gram of dry polymer.

[0023] In other features, the electrode comprises 1.0-1.6 wt% conductive material.

[0024] In other features, the electrode comprises any combination or combinations of the formulations described above and below.

[0025] The present invention discloses the following solutions:

[0026] Solution 1. An electrode for a lithium-ion battery, comprising:

[0027] an electrochemically active material comprising lithium;

[0028] a conductive material comprising carbon; and

[0029] A binder material comprising a polymer having a molecular weight greater than 800 kilodaltons or acid-modified polyvinylidene fluoride.

[0030] Option 2. The electrode according to Option 1, comprising 92-98.5 wt % of the electrochemically active material.

[0031] Option 3. The electrode according to Option 1, comprising 96-97.5 wt % of the electrochemically active material.

[0032] Option 4. The electrode according to Option 1, comprising 0.6-4 wt% of the conductive material.

[0033] Option 5. The electrode according to Option 1, comprising 0.8-2 wt% of the conductive material.

[0034] Option 6. The electrode according to Option 1, comprising 1-4 wt% of the binder material.

[0035] Option 7. The electrode according to Option 1, comprising 1.5-2.5 wt% of the binder material.

[0036] Option 8. An electrode according to Option 1, wherein the electrochemically active material comprises a phosphate polyanion.

[0037] Option 9. The electrode according to Option 1, wherein the electrochemically active material comprises a surface area greater than or equal to 6 m 2 / g of phosphate polyanion.

[0038] Option 10. An electrode according to Option 1, wherein the electrochemically active material comprises phospholipids.

[0039] Scheme 11. The electrode according to Scheme 1, wherein the electrochemically active material is selected from Li x MPO4, where M = Mn, Fe, Co and Ni.

[0040] Scheme 12. The electrode according to Scheme 1, wherein the electrochemically active material is selected from LiMn x Fe y PO4, where x+y=1.

[0041] Option 13. An electrode according to Option 1, wherein the electrochemically active material is selected from LiFe(P2O7), LiFe4(P2O7)3, LiV2(PO4)3, LiVOPO4, LiV2(PO4)3 and LiVPO4F.

[0042] Option 14. An electrode according to Option 1, wherein the conductive material is selected from carbon black (CB), acetylene black (AB) carbon, furnace black (FB) carbon, graphene nanosheets (GNPs), carbon nanofibers (CNFs), graphene (G), graphene oxide (GO), reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs) and / or single-walled carbon nanotubes (SWCNTs), and blends thereof.

[0043] Option 15. An electrode according to Option 1, wherein the conductive material comprises acetylene black (AB) carbon and multi-walled carbon nanotubes (MWCNTs) or comprises furnace black (FB) carbon and multi-walled carbon nanotubes (MWCNTs).

[0044] 16. The electrode according to 1, comprising 96.5-97.25 wt % of the electrochemically active material.

[0045] Item 17. The electrode according to Item 1, comprising 1.5-2.1 wt % of the binder material.

[0046] 18. The electrode of claim 1 , wherein the polymer has a molecular weight greater than 800 kilodaltons and less than 1200 kilodaltons.

[0047] 19. The electrode of 1, wherein the polymer comprises acidic chemical functional groups along the polymer backbone, wherein the acid content is greater than 0.1 milliequivalents / gram of dry polymer.

[0048] Item 20. The electrode according to Item 1, comprising 1.0-1.6 wt % of the conductive material.

[0049] 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 intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The present disclosure will be more fully understood from the detailed description and accompanying drawings, in which:

[0051] Figure 1 An example of a lithium-ion battery pack is shown.

[0052] Figure 2 Schematically shows a microscopic view of particles of cathode active material (CAM), such as lithium iron phosphate (LFP);

[0053] Figure 3 A system for manufacturing an electrode is shown;

[0054] Figure 4 The binding strength of electrodes comprising polymer binders with different molecular weights is shown.

[0055] Figure 5 The bonding strength of electrodes containing different polymer binders is shown;

[0056] Figure 6 shows improved resistance of an LFP cathode with MWCNTs added to a conductive carbon package; and

[0057] Figure 7 Shown from Figure 6 The LFP cathode has improved capacity retention with charge cycles.

[0058] In the drawings, reference numerals may be repeated to designate similar and / or identical elements. DETAILED DESCRIPTION

[0059] Lithium-ion batteries can be of different types. For example, lithium iron phosphate (LFP) batteries use LFP as the cathode active material and graphite carbon as the anode. Lithium manganese iron phosphate (LMFP) batteries use a cathode that contains manganese as an additional component. In LFP batteries, the cathode is formed by preparing a slurry of active material (e.g., LFP), additives (e.g., conductive filler materials), and a binder (e.g., a polymer). The slurry is then dried to form the cathode.

[0060] Electrodes containing LFP particles present unique challenges in slurry and electrode processing, as well as electrochemical performance, due to the electrode material's high surface area (small primary particle size) and low intrinsic conductivity. Consequently, fabricating LFP cathodes with good electrochemical and mechanical properties can be difficult. This is particularly prevalent with thicker electrodes for long-range electric vehicle applications.

[0061] Specifically, due to the high surface area (small primary particle size), the processability of LFP cathode slurries with low solids content of 35-45 wt% is challenging. LFP cathodes exhibit low intrinsic conductivity, which hinders electrochemical performance. Energy density is measured in watt-hours per kilogram (Wh / kg) and is the amount of energy that a battery can store relative to the mass of the battery. In order to improve conductivity and increase energy density, electrodes are typically compressed to higher weight densities. It is difficult to compress LFP electrodes to high density (low porosity) due to current collector delamination or physical cracking of the coating. Therefore, it is difficult to manufacture LFP cathodes with desirable electrochemical and mechanical properties.

[0062] The present disclosure provides a formulation for an LFP electrode that improves slurry processability, electrode durability, and compressibility. The electrode formulation also minimizes (reduces) internal resistance to improve the electrochemical performance of the LFP electrode. The electrode formulation solves the above-mentioned problems by forming an LFP cathode using a unique combination of a polymer binder and a conductive carbon additive to increase the solid content of the slurry to >55 wt %, and compress the resulting electrode coating to a porosity as low as 25 vol % (i.e., high density). The electrode formulation maximizes the amount of active material without compromising the durability and conductivity of the electrode. As a result, the resulting LFP cathode exhibits improved electrochemical and mechanical properties, as described in detail below.

[0063] Figure 1 An example of a lithium-ion battery 100 is schematically shown. The lithium-ion battery 100 includes a cathode (K+) 102, an anode (A-) 104, a separator 106, an electrolyte 108, and current collectors 110 and 112. The cathode 102 is a positive electrode. The anode 104 is a negative electrode. During charging, lithium ions flow from the cathode 102 through the separator 106 and the electrolyte 108 to the anode 104, as shown by arrow 120. During discharge (i.e., supplying power from the lithium-ion battery 100 to a load), lithium ions flow from the anode 104 through the separator 106 and the electrolyte 108 to the cathode 102, as shown by arrow 122.

[0064] Figure 2 A microscopic view of a typical LFP cathode active material (CAM) before processing (i.e., before adding solvent, binder, and conductive carbon) is schematically shown. The active material has low intrinsic conductivity. Smaller LFP primary particles (e.g., 100-400 nm in size) are sintered into a secondary structure with larger particles (e.g., 5-20 microns in diameter). The high surface area of ​​the primary particles provides significant interfacial area for charge transfer to the electrolyte solution and provides a shorter solid-state diffusion path for lithium ions, while the larger secondary structure provides improved slurry processability. As a result, the electrode includes many void spaces 150 between and within the secondary structure to enable efficient ion transport of lithium (Li) to the electrochemically active sites.

[0065] During processing, solvent and polymer binder flow into the void space 150. Due to the internal void space 150 within the LFP secondary structure, more solvent and polymer binder are required. A higher solvent content means a lower slurry solids content and increased drying time (lower manufacturing speed). When an electrode with a higher solvent content dries quickly, it can also cause the electrode to crack. In addition, if the polymer binder is absorbed into the LFP secondary structure, less binder is left to provide cohesion between the particles, which results in poor durability / flexibility of the electrode. A higher polymer binder content improves the durability and flexibility of the electrode. On the other hand, a higher polymer binder content further reduces the electrode energy density and increases the internal resistance because the polymer binder also has low electrical conductivity. In order to reduce the resistance of the polymer binder, a conductive carbon additive is added, which further reduces the energy density. The electrode formulation of the present disclosure solves these problems as follows.

[0066] Figure 3 A system 200 for manufacturing an LFP cathode according to the present disclosure is shown. An active material (e.g., LFP) 202, a conductive filler (additive) 204, and a polymer binder 206 are mixed with a solvent 208 in a mixer (not shown) to form a slurry 210 until the slurry 210 becomes viscous. The viscous slurry 210 is spread onto an aluminum current collector and dried (indicated by arrow 211) to form an LFP cathode (electrode) 212. The dried material is then cut to form LFP cathodes (electrodes) 212 of various sizes. The LFP cathode of the present disclosure is formed using the following polymer binder and conductive filler, which solves the above-mentioned problems.

[0067] For example, the solvent for forming the electrode slurry includes N-methylpyrrolidone (NMP). For example, the polymer binder includes a functionalized polyvinylidene fluoride (PVDF) homopolymer. PVDF is functionalized (treated) to improve adhesion and reduce the gelation of the slurry over time (i.e., increase viscosity over time). The functionalized polymer binder improves the cohesion between the LFP particles and the adhesion to the current collector, which in turn improves the durability of the LFP cathode. The functionalized polymer binder allows the use of a lower binder content, which improves energy density. For example, PVDF is functionalized (treated) using acid functionalization (treatment). For example, the acid used to functionalize (treat) PVDF may include carboxylated or sulfonated comonomers along the polymer backbone.

[0068] For example, conductive fillers include a combination of carbon black (CB) and carbon nanotubes (CNTs) to improve the conductivity of the LFP cathode. The combination of carbon black (CB) and carbon nanotubes (CNTs) improves the conductivity within the carbon-binder domain surrounding the LFP secondary structure. The primary carbon particles within the structured CB aggregates have a diameter (e.g., 10-40 nanometers) smaller than the active LFP material (e.g., 5-20 microns). The smaller diameter of the primary carbon particles within the structured CB aggregates (CB particles) provides many contact points. The conductive particles provide short-range electrical connections (paths) between the active material (LFP) particles. The CNTs can be long (e.g., up to a few microns). For example, the aspect ratio of the CNTs can be greater than 30. The CNTs provide long-range electrical connections (paths). The CB particles provide connections (electrical paths) between the active material (LFP) particles and the CNTs. The CB particles connect the active material (LFP) particles to the long-range electrical connections (paths) provided by the CNTs via the short-range electrical connections (paths). Therefore, the CB particles and the CNTs increase the electrical conductivity between the active material (LFP) particles.

[0069] The following are examples of various formulations for making cathodes according to the present disclosure that solve the above-mentioned problems. Cathode formulations according to the present invention using phosphate polyanions (or their blends) as active materials in combination with conductive fillers and binders with high aspect ratios (such as modified PVDF and other high molecular weight polymers) may include the following materials. The cathode formulations have the following technical advantages: 1) Increasing the solid content of the slurry to >55 wt%, which means using less solvent and shortening the drying time (increasing manufacturing speed). 2) Reducing electrode resistance (i.e., electrical resistance and charge transfer resistance) and improving long-term cycle life. 3) Improved compressibility leads to high energy density batteries (mechanical strength and durability) while using cheaper electrolytes.

[0070] The active materials in the formulations comprise a class of materials known as phosphate polyanions (or blends thereof). Such active materials may include any of the following: 1) high surface area phosphate polyanions (e.g., ≥ 6 m 2 / g). 2) Phospholipids, Li x MPO4 (wherein M = Mn, Fe, Co, Ni, etc., or a combination thereof), such as LiFePO4 (LFP) and LiMn x Fe y PO4(LMFP), where x+y=1.3) Other examples of phosphate polyanions include LiFe(P2O7), LiFe4(P2O7)3, LiV2(PO4)3, LiVOPO4, LiV2(PO4)3, and LiVPO4F. The active material content may be 92-98.5% (e.g., 96-97.5%), where % is weight %.

[0071] For example, the LFP cathode active material (CAM) used in the present disclosure has a primary particle size of 150-250 nm and spherical secondary aggregates with a median diameter of 8-13 microns. The CAM also has an internal porosity of ~13% v / v for the secondary aggregates. Throughout this disclosure, the symbol ~ represents about or approximately (i.e., indicating a range between ±0.5% and ±5%).

[0072] The polymer binder in the formulation includes the following materials: 1) High molecular weight PVDF binder, wherein M w >800 kilodaltons (kD) but <1200 kD. 2) Melting point is T melt PVDF binder at temperatures >160°C to improve membrane strength and reduce electrolyte swelling. 3) Acid-functionalized PVDF with meq acid / g polymer >0.10 to improve cohesion between particles, adhesion to aluminum current collector, and to prevent gelation of the slurry over time (e.g., by modification with carboxylated or sulfonated comonomers). Ion exchange capacity is expressed in milliequivalents / gram (meq g -1 )H+ form of dry ionomer. The binder content may be 0.75-4 wt% (e.g., 1.5-2.5 wt%).

[0073] The PVDF binders used in this application are listed in Table 1.

[0074]

[0075] Table 1. PVDF binder polymers described in this disclosure.

[0076] The conductive filler in the formulation includes the following materials. The combination of conductive additives includes carbon black (CB), acetylene black (AB) carbon (abbreviated as AB), furnace black (FB) carbon (abbreviated as FB), graphene nanoplatelets (GNPs), carbon nanofibers (CNFs), graphene (G), graphene oxide (GO), reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs) and / or single-walled carbon nanotubes (SWCNTs), and blends thereof. The conductive filler content can be 0.6-4% (e.g., 1-2%), where % is weight%. The physical properties of the conductive carbon additives used in this application are listed in Tables 2 and 3.

[0077]

[0078] Table 2. Carbon black powders described in this disclosure.

[0079] Carbon nanotube properties MWCNT1 MWCNT2 SWCNT #wall ～6-7 ～6-7 ～1-2 Diameter (D, nm) ～10 ～10 ～2 Length (L, nm) ～120 ～5000 ～5000 Aspect ratio (L / D) ～12 ～500 ～2500 <![CDATA[Surface area (m 2 / g)]]> ～300 ～300 ～400

[0080] Table 3. Carbon nanotube dispersions described in this disclosure.

[0081] Figure 4-7 Illustrated is the inventive combination of both conductive carbon and PVDF binder packages for an LFP cathode coating to increase the peel strength ( Figure 4 and 5 ), reduce the resistance ( Figure 6 ), and cycle life ( Figure 7 ). In the following description, although FB is not discussed separately, using FB in place of AB provides results comparable to those when using AB, although as described below using AB provides better results than using FB in place of AB.

[0082] Figure 4 Shows the effect of the molecular weight of the polymer binder on the adhesion and durability of the LFP electrode and the slurry viscosity. The peel strength is shown on the Y-axis at 270 and the molecular weight of the polymer binder is shown on the X-axis at 272. The peel strength is the magnitude of the force per unit width required to peel the material from the current collector.

[0083] In Figure 4 , each LFP cathode contains 95.5% LFP, and a combination of 0.5% carbon-based conductive filler AB and 1% MWCNT of CNT. The amounts of the active material (LFP) and the conductive filler are the same in each of the three LFP electrodes. The molecular weight of the polymer binder is different in each of the 3 electrodes, as shown below.

[0084] In Figure 4 , the LFP electrode having the peel strength shown at 274 contains a low molecular weight (PVDF1) polymer binder. The LFP electrode having the peel strength shown at 276 contains a high molecular weight (PVDF2) polymer binder. The LFP electrode having the peel strength shown at 278 contains an ultra-high molecular weight (PVDF3) polymer binder. PVDF1 < PVDF2 < PVDF3. For example, PVDF1 ~ 500 kDa, PVDF2 ~ 1000 kDa, and PVDF3 ~ 1370 kDa. The peel strength is proportional to the molecular weight of the homopolymer binder. The LFP electrode formulations used in this disclosure are summarized in Table 4. Slurry #1 is commonly used and exhibits the problems described above, so it will not be described further below. Throughout the following description, the terms PVDFn and PVDF#n may be used interchangeably and synonymously, where n = 1, 2, 3, or 4.

[0085]

[0086]

[0087] Table 4. LFP electrode slurry formulations described in this disclosure.

[0088] Although not shown, at the same solid content, slurry #2 having a high molecular weight polymer binder exhibited lower viscosity than slurry #3 containing an ultra-high molecular weight (PVDF3) polymer binder. In addition, although not shown, the electrode formed using slurry #2 and coated with a high molecular weight (PVDF2) polymer binder exhibited a longer cycle life than the LFP electrode formed using slurry #3 and coated with an ultra-high molecular weight polymer binder.

[0089] Therefore, using a low molecular weight (PVDF1) polymer binder can form a slurry with less solvent (high solid content), which is easy to process and dries quickly, but has the weakest peel strength (worst mechanical durability). Using an ultra-high molecular weight (PVDF3) polymer binder requires more solvent (low solid content) to process the slurry and takes longer to dry, but has the strongest peel strength (highest mechanical durability). Therefore, using a high molecular weight (PVDF2) polymer binder provides a good balance between peel strength (medium solid content and highest mechanical durability) and cycle life (high) compared to using a low molecular weight (PVDF1) polymer binder and an ultra-high molecular weight polymer binder (PVDF3).

[0090] exist Figure 5 In the figure, the peel strengths of the three LFP electrodes are shown at 284 (paste #2), 286 (paste #4), and 288 (paste #5). Figure 5 In the graph, peel strength is shown on the Y-axis at 280, and LFP cathodes containing different modified PVDF binders are shown on the X-axis at 282. Each of the three LFP cathodes contains a combination of 0.5% carbon-based conductive filler AB and 1% MWCNT. Each LFP electrode shown at 284 and 286 contains 95.5% LFP. The LFP electrode shown at 288 contains 96.4% LFP. The PVDF binder in each of the three LFP cathodes is different, as shown below.

[0091] The LFP electrode shown at 284 contains 3% homopolymer PVDF #2 as a binder. The LFP electrode shown at 286 contains 3% modified PVDF called PVDF #4 (modified or functionalized using acid treatment as described above) as a binder. The LFP electrode shown at 288 contains only 2.1% PVDF #4.

[0092] Electrodes containing modified PVDF (Slurry #4) exhibited twice the adhesive strength of electrodes containing unmodified PVDF (Slurry #2) of equivalent molecular weight and binder content. Furthermore, in formulations containing modified PVDF, the binder content could be reduced to 2.1% (Slurry #5) while still maintaining high peel strength and energy density. Acid modification improves the adhesion of the polymer binder to the LFP particle surface and the aluminum current collector.

[0093] The cycle life of the LFP electrode formed using slurry #2 containing 3% unmodified PVDF shown at 284 is greater than the cycle lives of the LFP electrodes shown at 286 and 288. The cycle life of the LFP electrode formed using slurry #4 containing 95.5% LFP and 3% PVDF #4 shown at 286 is only slightly greater than the cycle life of the LFP electrode formed using slurry #5 containing 96.4% LFP (increasing the amount of active material) and 2.1% PVDF #4 (reducing the amount of binder) shown at 288.

[0094] Thus, the combination of using a formulation of 96.4% LFP (increasing the amount of active material), 0.5% carbon-based conductive fillers AB and CNTs 1% MWCNTs, and 2.1% PVDF2 (reducing the amount of binder) not only provides good peel strength as shown at 288, but also provides good cycle life performance.

[0095] exist Figure 6 , the resistance of LFP cathodes containing different carbon-based conductive fillers is shown. Resistance is shown on the Y-axis at 250. Different carbon-based conductive fillers are shown on the X-axis at 252. The resistance of an LFP cathode formed using slurry #6 containing the carbon-based conductive filler acetylene black (AB) is shown at 254. The resistance of an LFP cathode formed using slurry #7 containing a combination of carbon-based conductive fillers acetylene black (AB) and Ketjen black (KB) (i.e., AB+KB) is shown at 256. The resistance of an LFP cathode formed using slurry #2 containing a combination of carbon-based conductive fillers acetylene black (AB) and MWCNTs (i.e., AB+CNT) is shown at 258.

[0096] exist Figure 6In each of the three LFP cathodes, the amount of active material (LFP) and binder was the same in each of the three LFP electrodes. The amount of carbon-based conductive filler was also the same, but the composition of the carbon-based conductive filler was different in each of the three LFP cathodes, as described below. In the LFP electrode shown at 254, the amount of AB was 1.5% (slurry #6). In the LFP electrode shown at 256, the amount of AB was 1% and the amount of KB was 0.5% (slurry #7). In the LFP electrode shown at 258, the amount of AB was 0.5% and the amount of CNT was 1% (CNT was MWCNT) (slurry #2)

[0097] The LFP electrode shown at 258 comprising 95.5% LFP, 3% PVDF binder, AB 0.5% and CNT 1% MWCNT exhibits much lower resistance (higher conductivity) than the LFP electrode shown at 254 comprising 95.5% LFP, 3% PVDF binder, 1.5% AB and the LFP electrode shown at 256 comprising 95.5% LFP, 3% PVDF binder, 1% AB and 0.5% KB.

[0098] The LFP electrode shown at 254 comprising 95.5% LFP, 3% PVDF binder, 1.5% AB exhibits a higher resistance (lower conductivity) than the LFP electrode shown at 258 comprising 95.5% LFP, 3% PVDF binder, 0.5% AB and CNT 1% MWCNT, but exhibits a lower resistance (higher conductivity) than the LFP electrode shown at 256 comprising 95.5% LFP, 3% PVDF binder, AB 1% and KB 0.5%.

[0099] The cycle life of the three LFP electrodes is Figure 7 The Y-axis shows the amount of charge retained (retention) at 260. Figure 6 The cycle life of paste #5, which has the lowest internal electronic resistance in Table 5, was improved.

[0100] Thus, the LFP electrode shown at 258 exhibits lower resistance and higher cycle life (charge retention) than the LFP electrodes shown at 254 and 256. The LFP electrode shown at 254 exhibits higher resistance and lower cycle life than the LFP electrode shown at 258. Thus, the combination of conductive fillers (additives) with different aspect ratios (AB vs. CNT) improves the electrochemical performance of the LFP electrode. Specifically, the addition of a combination of carbon-based conductive fillers AB 0.5% and MWCNT 1% to the formulation of the LFP electrode comprising 95.5% LFP and 3% PVDF binder improves electrochemical performance.

[0101] Table 4 lists the formulations described in this disclosure and additional formulations, and lists their measured internal resistance, ionic resistance, and charge transfer resistance. Table 4 demonstrates that the electronic and charge transfer resistances dominate the electrode resistance. Other examples of electrodes with improved electrochemical performance are also listed, such as slurries #8 and #9 containing CB, MWCNT, and PVDF4. Table 4 shows that LFP electrodes formed using slurries 4, 5, 8, and 9 provide much lower resistance than the other slurries.

[0102] Therefore, in the above reference Figure 4-7 In the examples shown and described, in the formulation of the LFP electrode according to the present disclosure, the active material content can be increased, the binder content can be reduced, the binder can include an acid-functionalized ultra-high molecular weight polymer, and the conductive additive can be a combination of AB (or FB) and MWCNT. This formulation provides good mechanical and electrochemical properties as described above.

[0103] The formulation is described above with reference to LFP as the active material. The above teachings are equally applicable to any active material in the entire class of active materials listed or described above with reference to phosphate polyanions (or blends thereof). As a non-limiting example, the above teachings are equally applicable to LMFP and the other active materials listed or described above.

[0104] The foregoing description is illustrative only and is in no way intended to limit the present disclosure, its application, or use. The broad teachings of the present disclosure can be implemented in various forms. Therefore, although this disclosure includes specific examples, the true scope of the disclosure should not be limited thereto, as other modifications will become apparent upon a study of the drawings, the specification, and the following claims.

[0105] It should be understood that one or more steps within the method may be implemented in a different order (or simultaneously) without changing the principles of the present disclosure. In addition, although the various embodiments are described above as having certain features, any one or more features described with respect to any embodiment of the present disclosure may be implemented in any other embodiment and / or combined with the features of any other embodiment, even if the combination is not explicitly described. In other words, the embodiments are not mutually exclusive, and the mutual permutation of one or more embodiments remains within the scope of the present disclosure. The phrase "at least one of A, B, and C" as used herein should be interpreted to mean a logic (A or B or C) using a non-exclusive logical OR, and should not be interpreted to mean "at least one of A, at least one of B, and at least one of C."

Claims

1. An electrode for a lithium-ion battery pack, comprising: an electrochemically active material comprising lithium; a conductive material comprising carbon; and A binder material comprising a polymer having a molecular weight greater than 800 kilodaltons or acid-modified polyvinylidene fluoride.

2. The electrode of claim 1, wherein the electrochemically active material comprises a surface area greater than or equal to 6 m 2 / g of phosphate polyanion.

3. The electrode of claim 1, wherein the electrochemically active material comprises phospholipids.

4. The electrode according to claim 1, wherein the electrochemically active material is selected from Li x MPO4, where M = Mn, Fe, Co and Ni.

5. The electrode according to claim 1, wherein the electrochemically active material is selected from LiMn x Fe y PO4, where x+y=1.

6. The electrode according to claim 1, wherein the electrochemically active material is selected from the group consisting of LiFe(P2O7), LiFe4(P2O7)3, LiV2(PO4)3, LiVOPO4, LiV2(PO4)3 and LiVPO4F.

7. The electrode according to claim 1, wherein the conductive material is selected from carbon black (CB), acetylene black (AB) carbon, furnace black (FB) carbon, graphene nanoplatelets (GNPs), carbon nanofibers (CNFs), graphene (G), graphene oxide (GO), reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs) and / or single-walled carbon nanotubes (SWCNTs), and blends thereof. 8 . The electrode according to claim 1 , wherein the conductive material comprises acetylene black (AB) carbon and multi-walled carbon nanotubes (MWCNTs) or comprises furnace black (FB) carbon and multi-walled carbon nanotubes (MWCNTs).

9. The electrode of claim 1, comprising 96.5-97.25 wt% of the electrochemically active material, 1.0-1.6 wt% of the conductive material, and 1.5-2.1 wt% of the binder material.

10. The electrode according to claim 1, wherein: The polymer comprises acidic chemical functional groups along the polymer backbone, wherein the acid content is greater than 0.1 milliequivalents per gram of dry polymer; or The molecular weight of the polymer is greater than 800 kilodaltons and less than 1200 kilodaltons.

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