Patent Application
20240204197
The present invention relates to a cathode composition and a method of producing same. More particularly, the cathode composition of the present invention is intended to provide high capacity and high retention thereof.
In particular, the cathode composition of the present invention is intended for use in lithium-ion batteries.
Presently, conductive carbon materials are used in lithium-ion batteries in an effort to improve the electrical conductivity of electrochemically active material in both the anodes and cathodes thereof. Carbon black (CB) is the most commonly used conductive additive, whilst commercially available graphite (for example TIMREX® KS 6 from Imerys Graphite & Carbon) is also utilised, as are carbon nanotubes (CNT) and vapour grown carbon fibres (VGCF).
In addition to improving electrical conductivity, carbon black is also understood to minimise heat generation within the battery cell.
CNT have a unique one-dimensional structure and provides what are known to be excellent mechanical, electrical and electrochemical properties. VGCF similarly provides an effective conductive network within the active material coating, which contributes to improved low temperature performance, longer cycle life, higher rate capability and lower volume expansion in the cell. Both CNT and VGCF are considered significant conductive additives—needing only very small loadings (<1%) to provide high conductivity, when compared with carbon black. Unfortunately, both CNT and VGCF are comparatively expensive (by tens of $/kg) and have significant safety concerns associated with their application (CNT in particular prompts an asbestos-like reaction in the lungs).
There would be significant advantage and benefit to providing an improved additive for lithium-ion battery cathodes, particularly an additive derived from a natural graphite precursor.
The cathode composition and method of the present invention have as one object thereof to overcome substantially one or more of the abovementioned problems associated with prior art processes, or to at least provide a useful alternative thereto.
The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. This discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.
Throughout the specification and claims, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
Throughout the specification and claims, unless the context requires otherwise, the term “oblate spheroid” or variations thereof refer to a surface of revolution obtained by rotating an ellipse about its minor axis. Put simply, an oblate spheroid is understood to be a flattened sphere, in which it is wider than it is high. Other terms that are to be understood to indicate substantially that same shape/form are “ellipsoidal” and “potato shaped”.
Throughout the specification and claims, unless the context requires otherwise, the term “flake” or variations thereof, is to be understood to indicate that the material referred to has a flake or flaky morphology or form.
Throughout the specification and claims, unless the context requires otherwise, references to “milling” are to be understood to include reference to “grinding”, and references to “grinding” are to be understood to include reference to “milling”.
Throughout the specification and claims, unless the context requires otherwise, D50 is to be understood to refer to the median value of the particle size distribution. Put another way, it is the value of the particle diameter at 50% in a cumulative distribution. For example, if the D50 of a sample is a value X, 50% of the particles in that sample are smaller than the value X, and 50% of the particles in that sample are larger than the value X.
The term “relative” or “relatively” used in respect of a feature of the invention is intended to indicate comparison to that feature in the prior art and the typical characteristics of that feature in the prior art, unless the context clearly indicates or requires otherwise.
It is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range. For example, a range from about 1 micrometer (μm) to about 2 μm, or about 1 μm to 2 μm, should be interpreted to include not only the explicitly recited limits of from between from about 1 μm to about 2 μm, but also to include individual values, such as about 1.2 μm, about 1.5 μm, about 1.8 μm, etc., and sub-ranges, such as from about 1.1 μm to about 1.9 μm, from about 1.25 μm to about 1.75 μm, etc. Furthermore, when “about” and/or “substantially” are/is utilised to describe a value, they are meant to encompass minor variations (up to +/−10%) from the stated value.
In accordance with the present invention there is provided a cathode composition, the cathode comprising a graphitic material additive, wherein the graphitic material additive comprises graphitic particles having a generally non-spheroidal form and a D50 of less than about 15 μm.
Preferably, the graphitic particles have a D50 of less than about 10 μm.
The non-spheroidal form of the graphitic particles preferably encompasses a form that approximates either an oblate spheroid or a flake form.
Still preferably, the graphitic particles have a carbon content of:
The graphitic particles preferably comprise either an agglomerated fines product or a high surface area (HSA) product.
Preferably, the agglomerated fines product comprises secondary graphite particles that predominantly have a form that approximates an oblate spheroid.
In one form of the present invention, the secondary graphite particles have a D50 of:
Preferably, the secondary graphite particles have a surface area of:
The compression density of the secondary graphite particles at 75 kf/cm2 is preferably in the range of about 1.0 to 1.5 g/cc.
The conductivity of the secondary graphite particles is preferably in the range of about 25 to 37 S/cm, for example about 31 S/cm.
Preferably, the secondary graphite particles comprise ground primary graphite particles.
Preferably, the HSA product comprises graphitic particles that have been subject to mechanical exfoliation. Mechanical exfoliation is preferably performed by way of milling, impact, pressure and/or shear forces.
Still preferably, the mechanical exfoliation is conducted:
The graphitic particles of the HSA product preferably have a surface area of:
In one form of the present invention the graphitic particles of the HSA product have been subject to mechanical exfoliation at greater than 200 kWh/t, for example in the range of 400 to 500 kWh/t, and have a surface area of greater than 20 m2/g, for example 25 to 35 m2/g.
In a further form of the present invention the graphitic particles of the HSA product have been subject to mechanical exfoliation at greater than 700 kWh/t, for example in the range of 1000 to 1200 kWh/t, and have a surface area of greater than 40 m2/g, for example 40 to 50 m2/g.
Preferably, the HSA product has a flake form.
The HSA product is preferably also subjected, after mechanical exfoliation, to drying methods that support the retention of its flake form, for example a cryogenic drying method.
Still preferably, the ground primary graphite particles further comprise a carbon-based material. The carbon-based material is preferably one or more of pitch, polyethylene oxide and polyvinyl oxide.
Preferably, the amount of carbon-based material in the secondary graphite particles is in the range of 2 to 10 wt % relative to graphite.
The ground primary graphite particles preferably have a D50:
Preferably, the ground primary graphite particles have a surface area of about 2 to 60 m2/g, for example 7 to 9 m2/g.
Preferably, the ground primary graphite particles have XRD characteristics of one or more of a d002 of >3.35 Å, an Lc of >1000 Å and an La of >1000 Å. In a preferred form, the ground primary graphite particles have XRD characteristics of each of a d002 of >3.35 Å, an Lc of >1000 Å and an La of >1000 Å, and a purity of >99.9%.
In one form, the secondary graphite particle of the graphitic material additive comprises an aggregate of primary graphite particles, the aggregate providing the approximate oblate spheroid form and having a D50 of less than about 5 microns.
The secondary graphite particles may, in one form of the invention, have a D50 of less than about 2 microns.
In one form, the graphitic material additive is derived from a natural graphite precursor.
In accordance with the present invention there is further provided a cathode composition comprising a cathode active material, a graphitic material additive, and a binder, wherein the graphitic material additive comprises graphitic particles having a generally non-spheroidal form and a D50 of less than about 15 μm.
Preferably, the graphitic particles have a D50 of less than about 10 μm.
The non-spheroidal form of the graphitic particles preferably encompasses a form that approximates either an oblate spheroid or a flake form.
In one form of the invention the cathode active material may be provided in the form of lithium cobalt oxide (LCO). In a further form the cathode active material may be provided in the form of nickel manganese cobalt (NMC).
In another form, the binder may be provided in the form of polyvinylidene fluoride (PVdF).
In accordance with the present invention there is further provided a lithium-ion battery comprising a cathode composition as described hereinabove.
In accordance with the present invention there is still further provided a method for producing a cathode composition as described hereinabove.
In accordance with the present invention there is yet still further provided a method of producing a graphitic material additive for use in a cathode composition, the graphitic material additive having a generally non-spheroidal form and a D50 of less than about 15 μm, the method comprising the steps of:
Preferably, the graphitic particles have a D50 of less than about 10 μm.
The mechanical exfoliation step is preferably performed by way of milling, impact, pressure and/or shear forces.
Still preferably, the mechanical exfoliation step is conducted:
The graphitic particles of the HSA product preferably have a surface area of:
In one form of the present invention the graphitic particles of the HSA product have been subject to mechanical exfoliation at greater than 200 kWh/t, for example in the range of 400 to 500 kWh/t, and have a surface area of greater than 20 m2/g, for example 25 to 35 m2/g.
In a further form of the present invention the graphitic particles of the HSA product have been subject to mechanical exfoliation at greater than 700 kWh/t, for example in the range of 1000 to 1200 kWh/t, and have a surface area of greater than 40 m2/g, for example 40 to 50 m2/g.
The drying step to which the HSA product is subjected, is preferably a cryogenic drying method.
Still preferably, the ground primary graphite particles further comprise a carbon-based material. The carbon-based material is preferably one or more of pitch, polyethylene oxide and polyvinyl oxide.
Preferably, the amount of carbon-based material in the secondary graphite particles is in the range of 2 to 10 wt % relative to graphite.
The present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawings, in which:—
The present invention provides a cathode composition, the cathode comprising a graphitic material additive, wherein the graphitic material additive comprises graphitic particles having a generally non-spheroidal form and a D50 of less than about 15 μm, for example less than about 10 μm.
The non-spheroidal form of the graphitic particles is understood to encompass a form that approximates either an oblate spheroid or a flake form.
The graphitic particles have a carbon content of greater than 99.9% wt/wt, for example greater than 99.92% wt/wt.
The graphitic particles comprise either an agglomerated fines product or a high surface area (HSA) product.
The agglomerated fines product comprises secondary graphite particles that predominantly have a form that approximates an oblate spheroid. In one form of the present invention, the secondary graphite particles have a D50 of less than about 5 μm, for example less than about 2 μm.
The secondary graphite particles have a surface area of about 2 to 60 m2/g, for example about 2 to 6 m2/g.
The compression density of the secondary graphite particles at 75 kf/cm2 is in the range of about 1.0 to 1.5 g/cc. The conductivity of the secondary graphite particles is in the range of about 25 to 37 S/cm, for example about 31 S/cm.
The secondary graphite particles comprise ground primary graphite particles. The HSA product comprises graphitic particles that have been subject to mechanical exfoliation. This mechanical exfoliation is performed by way of milling, impact, pressure and/or shear forces.
The mechanical exfoliation is conducted:
The graphitic particles of the HSA product have a surface area of:
The HSA product has a flake form.
The HSA product is also subjected, after mechanical exfoliation, to drying methods that support the retention of its flake form, for example a cryogenic drying method.
In one form of the present invention the graphitic particles of the HSA product have been subject to mechanical exfoliation at greater than 200 kWh/t, for example in the range of 400 to 500 kWh/t, and have a surface area of greater than 20 m2/g, for example 25 to 35 m2/g. This provides what is referred to herein as an HSA product 1, or HSA1.
In a further form of the present invention the graphitic particles of the HSA product have been subject to mechanical exfoliation at greater than 700 kWh/t, for example in the range of 1000 to 1200 kWh/t, and have a surface area of greater than 40 m2/g, for example 40 to 50 m2/g. This provides what is referred to herein as a HSA product 2, or HSA2.
The ground primary graphite particles further comprise a carbon-based material. The carbon-based material is, for example, one or more of pitch, polyethylene oxide and polyvinyl oxide.
The amount of carbon-based material in the secondary graphite particles is in the range of 2 to 10 wt % relative to graphite. The ground primary graphite particles have a DSO:
The ground primary graphite particles have a surface area of about 2 to 60 m2/g, for example 7 to 9 m2/g.
The ground primary graphite particles have XRD characteristics of one or more of a d002 of >3.35 Å, an Lc of >1000 Å and an La of >1000 Å. For example, in one form, the ground primary graphite particles have XRD characteristics of each of a d002 of >3.35 Å, an Lc of >1000 Å and an La of >1000 Å, and a purity of >99.9%.
In one form, the secondary graphite particle of the graphitic material additive comprises an aggregate of primary graphite particles, the aggregate providing the approximate oblate spheroid form and having a D50 of less than about 5 microns. The secondary graphite particles may, in one form of the invention, have a D50 of less than about 2 microns.
In one form, the graphitic material additive is derived from a natural graphite precursor.
The present invention further provides a cathode composition comprising a cathode active material, a graphitic material additive, and a binder, wherein the graphitic material additive comprises graphitic particles having a generally non-spheroidal form and a D50 of less than about 15 μm, for example less than about 10 μm.
The non-spheroidal form of the graphitic particles encompasses a form that approximates either an oblate spheroid or a flake form.
In one form of the invention the cathode active material may be provided in the form of lithium cobalt oxide (LCO). In a further form the cathode active material may be provided in the form of nickel manganese cobalt (NMC).
In another form, the binder may be provided in the form of polyvinylidene fluoride (PVdF).
The present invention further provides a lithium-ion battery comprising a cathode composition as described hereinabove. Still further, the present invention provides a method for producing a cathode composition as described hereinabove.
The present invention yet still further provides a method of producing a graphitic material additive for use in a cathode composition, the graphitic material additive having a generally non-spheroidal form and a D50 of less than about 15 μm, for example less than 10 μm, the method comprising the steps of:
The mechanical exfoliation step is, in one form, performed by way of milling, impact, pressure and/or shear forces. The mechanical exfoliation step is conducted:
The graphitic particles of the HSA product have a surface area of:
In one form of the present invention the graphitic particles of the HSA product have been subject to mechanical exfoliation at greater than 200 kWh/t, for example in the range of 400 to 500 kWh/t, and have a surface area of greater than 20 m2/g, for example 25 to 35 m2/g.
In a further form of the present invention the graphitic particles of the HSA product have been subject to mechanical exfoliation at greater than 700 kWh/t, for example in the range of 1000 to 1200 kWh/t, and have a surface area of greater than 40 m2/g, for example 40 to 50 m2/g.
The drying step to which the HSA product is subjected, is a cryogenic drying method.
In one form, the ground primary graphite particles further comprise a carbon-based material. The carbon-based material is, for example, one or more of pitch, polyethylene oxide and polyvinyl oxide. The amount of carbon-based material in the secondary graphite particles is in the range of 2 to 10 wt % relative to graphite.
The process of the present invention may be better understood with reference to the following non-limiting examples.
Table A below provides one non-limiting example of an appropriate ground primary graphite particle, a purified graphite fines precursor, for use in/as used in the method of the present invention, whilst Table B provides the elemental analysis thereof.
In a preferred form, the purified graphite has a carbon content of >99.9%, preferably >99.92%. Further, the purified graphite has a flake morphology with a particle size distribution with a D50 of less than 20 μm, for example less than 15 μm, and in turn less than 10 μm. Graphite fines are obtained by classifying a feed graphite material.
In the production of an agglomerated fines product in accordance with one form of the present invention, the ground primary graphite particles are spheronised and coated with a carbon-based material, after which they are pyrolysed, thereby producing the secondary particle that approximates an oblate spheroid. The carbon-based material is one or more of pitch, polyethylene oxide and polyvinyl alcohol. The amount of carbon-based material used in coating the ground primary graphite particles is in the range of 2 to 10 wt % relative to graphite. The temperature of pyrolysis is between about 880° C. to 1100° C. The time for pyrolysis is in the range of about 12 to 40 hours, including both heating and cooling periods.
The present Applicants describe the ground primary graphite particles and their production, in addition to secondary graphite particles of the present invention, in International Patent Application PCT/IB2020/058910, and the entire content thereof is explicitly incorporated herein by reference.
The natural graphite precursor used for the present investigation was extracted from the Vittangi graphite mine in the County of Norrbotten in northern Sweden. This natural graphite source is characterised by hard particles having a very narrow distribution, with microcrystalline flake. The graphite was then chemical purified at the Applicant's pilot plant in Rudolstadt.
The SEM image of
A series of experiments have been undertaken by or on behalf of the Applicants to investigate the performance of a range of cathode compositions utilising different graphitic material additives.
The cathode composition of cathode active material/binder/graphitic material employed in the conductive additive tests is:
LCO designates lithium cobalt oxide, PVdF designates polyvinylidene fluoride, and Cmix represents the particular graphitic material additive employed.
Table 1 shows the range of experiments conducted and the particular graphitic material additive employed.
Table 2 provides detail of each of the various graphitic material additives. Various graphitic materials from the Applicant are noted, including T-20 which, as noted hereinafter, are a mix with carbon black in a ratio of 2:1.
The cycling testing steps employed were as follows:
The results of experiments 1 and 2 are provided in Table 3 below. References throughout to ‘see attachment’ refer to later Tables in which IR is referenced.
The results of experiments 3 and 4 are provided in Table 4 below.
The results of experiments 5 and 6 are provided in Table 5 below.
The results of experiment 7 are provided in Table 6 below.
The average data of experiments 1 to 7 is provided in Table 7 below with FCE/FCL represented graphically in
The average data of experiments 1 to 7 is again provided in Table 8 below, with a capacity retention comparison (coating density) shown in
The conclusions drawn by the Applicants from this series of experiments include:
Testing was undertaken to investigate the powder resistance, both at similar density after pressure and at similar pressure.
The results of powder resistive testing under similar density after pressure are shown in Table 9 below.
The results of powder resistive testing under similar pressure are shown in Table 10 below.
The Applicants have drawn the following conclusions regarding powder resistance:
The production of the agglomerated fines product is described hereinabove. The production of the high surface area (HSA) products includes a mechanical exfoliation step that can advantageously be carried out using one of milling, impact, pressure, and/or shear forces.
A primary graphite material mechanically exfoliated with 200-500 kWh/t, for example 400-500 kWht/t, energy produces HSA1. The HSA1 product has a surface area of 20 to 40 m2/g, for example 25-35 m2/g.
A primary graphite material mechanically exfoliated with 700 to 1200 kWh/t, for example 1000 to 1200 kWht/t, energy produces HSA2. The HSA2 product has a surface area of 40 to 80 m2/g, for example 40-50 m2/g.
In a preferred form an exfoliated slurry from the mechanical exfoliation step is dried using special drying methods to retain the flake morphology. The special drying method can include a cryogenic drying method. Such a cryogenic method freezes the slurry and sublimates the ice into vapor. An example of suitable process conditions includes the freezing of the slurry into a solid block, followed by subjecting the block to:
The Applicants understand that using typical drying methods, such as a hot air oven, will cause flakes to agglomerate, thereby providing an inferior primary graphite material with relatively reduced surface area.
The particle size of HSA1 and HSA2 are D50 less than 15 μm for example D50 less than 10 μm.
A further series of tests were undertaken by the Applicant to evaluate the Applicant's graphitic material additives compositions in accordance with the present invention in NMC111 cathodes, NMC referencing Nickel Manganese Cobalt.
The details of the agglomerated fines (AF) and high surface area (HSA1 and HSA2) graphitic particles of the composition of the present invention utilised in these tests is set out in Table 11 below.
The components of the cathode include active material (93 wt. %), Binder/PVDF (3%) and conductive additive (4%). In one test system, the Applicant's graphitic material additives were used as the only additive. In another test system, the Applicant's graphitic material additives were combined with Carbon Black (CB) (reference) in 1:1 ratio (2% each). The CB alone (4%) was used as a reference. The following Table 12 summarises the components of this test system.
In
Table 13 below provides a summary of the test results in terms of conductivity, coating weight and strength.
Conductivity values of electrodes (Electrode conductivity S/cm) with HSA1 and HSA2 in 1:1 ratio with CB was higher (3×) than reference alone. It is believed that this result may indicate that a relatively smaller amount of conductive agent can be added (less than 4 wt. % for example in this case) to achieve a required conductivity, and a higher amount of active cathode material can be added which will in turn increase battery capacity.
Calender density of electrodes with Applicant's graphitic material additives was higher compared to reference. Calendering can be defined as compressing of dried electrode material to reduce porosity, improve particle contacts and enhance the energy density. At the same applied calender pressure, Applicant's graphitic material additive containing electrode achieved higher densities. It is believed that this result may indicate that electrodes prepared with the cathode composition of the present invention can be compressed more/occupy smaller volume, and therefore the volumetric energy density will increase relative to the prior art. At a macroscale, this is understood to indicate relatively smaller/lighter batteries for the same drive length. Table 14 below summarises the calenderability and electrochemical cycling of respective graphitic material additives.
All electrochemical performance properties were consistent with (within experimental variation) the reference system. This indicates the Applicant's graphitic material additives do not have any untoward effect towards the active cathode material performance. All values are % of reference (CB alone).
Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021901988 | Jun 2021 | AU | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2022/056091 | 6/30/2022 | WO |
