Classifications

• • H—ELECTRICITY
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
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• • H—ELECTRICITY
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
  • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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  • C01G53/00—Compounds of nickel
  • C01G53/40—Complex oxides containing nickel and at least one other metal element
  • C01G53/42—Complex oxides containing nickel and at least one other metal element containing alkali metals, e.g. LiNiO2
  • C01G53/44—Complex oxides containing nickel and at least one other metal element containing alkali metals, e.g. LiNiO2 containing manganese
  • C01G53/50—Complex oxides containing nickel and at least one other metal element containing alkali metals, e.g. LiNiO2 containing manganese of the type (MnO2)n-, e.g. Li(NixMn1-x)O2 or Li(MyNixMn1-x-y)O2
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  • C01G53/40—Complex oxides containing nickel and at least one other metal element
  • C01G53/66—Complex oxides containing nickel and at least one other metal element containing alkaline earth metals, e.g. SrNiO3 or SrNiO2
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  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G53/00—Compounds of nickel
  • C01G53/80—Compounds containing nickel, with or without oxygen or hydrogen, and containing one or more other elements
  • C01G53/82—Compounds containing nickel, with or without oxygen or hydrogen, and containing two or more other elements
• • H—ELECTRICITY
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  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
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  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
• • H—ELECTRICITY
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  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
• • H—ELECTRICITY
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  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
  • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
• • C—CHEMISTRY; METALLURGY
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  • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
  • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
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  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/40—Electric properties
• • H—ELECTRICITY
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  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/028—Positive electrodes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/49002—Electrical device making
  • Y10T29/49108—Electric battery cell making

Definitions

• the present invention relates to novel doped nickelate-containing compositions and their method of preparation, to electrodes containing the novel doped nickelate-containing compositions, and to the use of these electrodes, for example in energy storage devices.
• Sodium-ion batteries are analogous in many ways to the lithium-ion batteries that are in common use today; they are both reusable secondary batteries that comprise an anode (negative electrode), a cathode (positive electrode) and an electrolyte material, both are capable of storing energy, and they both charge and discharge via a similar reaction mechanism.
• Na + (or Li + ) ions de- intercalate from the cathode and insert into the anode.
• charge balancing electrons pass from the cathode through the external circuit containing the charger and into the anode of the battery. During discharge the same process occurs but in the opposite direction.
• Lithium-ion battery technology has enjoyed a lot of attention in recent years and provides the preferred portable battery for most electronic devices in use today; however lithium is not a cheap metal to source and is considered too expensive for use in large scale applications.
• sodium-ion battery technology is still in its relative infancy but is seen as advantageous; sodium is much more abundant than lithium and some researchers predict this will provide a cheaper and more durable way to store energy into the future, particularly for large scale applications such as storing energy on the electrical grid. Nevertheless a lot of work has yet to be done before sodium-ion batteries are a commercial reality.
• NaNio.5Mno.5O2 is a known Na-ion material in which the nickel is present as Ni 2+ while the manganese is present as Mn 4+ . The material is ordered with the Na and Ni atoms residing in discrete sites within the structure.
• the nickel ions (Ni 2+ ) are a redox element which contributes to the reversible specific capacity and the manganese ions (Mn 4+ ) play the role of a structure stabilizer.
• Compound NaNio.5Tio.5O2 is analogous to NaNio.5Mno.5O2 in that the Ni 2+ ions provide the active redox centre and the Ti 4+ ions are present for structure stabilization.
• lithium-containing compounds of the formula Li[NixLi (1 3_2x/3 ) Mn(2/3-x/3 ) ]02 where the amount of nickel is less than 0.5 exhibit a significantly higher charge capacity than would be expected from conventional theoretical calculation.
• Lu and Dahn demonstrated that their lithium materials undergo a nonreversible loss of oxygen when they are charged to higher voltages, and these oxygen deficient materials then react reversibly with lithium. Notwithstanding this, although this increased charge capacity is a potentially interesting discovery, the commercial utility of such compounds is hindered by the high cost of lithium, as discussed above.
• US2007/0218361 teaches a sodium ion secondary battery which comprises a positive electrode active material which includes a sodium-containing transition metal oxide Na a Li M x 02 ⁇ a-
• the M includes at least two of manganese, iron, cobalt and nickel.
• the amount of sodium is neither too large (otherwise excess sodium oxide or sodium hydride is produced which causes the positive electrode to become highly moisture absorptive) nor too small.
• the amount of sodium ions that can be intercalated and de-intercalated is said to be reduced and this results in a high discharge capacity not being able to be obtained.
• This prior art describes that the optimum amount of sodium, i.e.
• the value of a is preferably 0.6 to 1.1 , further preferably 0.9 to 1.1 and more preferably 1. Meanwhile the amount of oxygen is also described as critical to performance. Too much oxygen is said to occupy transition metal and/or alkaline metal sites, and presumably this will hinder re-intercalation of the sodium ions during charge/discharge. Too little oxygen is said to produce material with a crystal structure with lots of defects. The optimum range for a is from 0 to 0.1. Another feature of the specific examples described in US2007/0218361 is that they all contain manganese in oxidation state +3. This is to allow sodium extraction by a manganese oxidation process (Mn +3 ⁇ Mn 4+ ).
• the present invention aims to provide a cost effective electrode that contains an active material that is capable of achieving a considerably higher specific charge capacity than would be expected from conventional theoretical calculations. Further, it is desirable for such active materials to be straightforward to manufacture and easy to handle and store. Further still, the present invention aims to provide an electrode which is able to be recharged multiple times without significant loss in charge capacity. In particular the present invention will provide an energy storage device that utilises an electrode of the present invention for use in a sodium-ion cell or a sodium metal cell.
• the present invention provides an electrode containing one or more active materials comprising:
• A comprises either sodium or a mixed alkali metal in which sodium is the major constituent
• M 1 is nickel in oxidation state less than or equal to 4+
• M 2 comprises a metal in oxidation state less than or equal to 4+
• M 3 comprises a metal in oxidation state 2+
• M 4 comprises a metal in oxidation state less than or equal to 4+
• M 5 comprises a metal in oxidation state 3+
• Preferred electrodes of the present invention contain one or more active materials comprising:
• A comprises either sodium or a mixed alkali metal in which sodium is the major constituent
• M 1 is nickel in oxidation state 4+
• M 2 comprises a metal in oxidation state 4+
• M 3 comprises a metal in oxidation state 2+
• M 4 comprises a metal in oxidation state 4+
• M 5 comprises a metal in oxidation state 3+
• Particularly preferred electrodes contain one or more active materials comprising:
• A comprises either sodium or a mixed alkali metal in which sodium is the major constituent
• M 1 is nickel in oxidation state less than 4+
• M 2 comprises a metal in oxidation state less than or equal to 4+
• M 3 comprises a metal in oxidation state 2+
• M 4 comprises a metal in oxidation state less than or equal to 4+
• M 5 comprises a metal in oxidation state 3+
• v 0, preferably 0 ⁇ v ⁇ 0.5 at least one of w and y is > 0
• M 2 comprises a metal selected from one or more of manganese, titanium and zirconium
• M 3 comprises a metal selected from one or more of magnesium, calcium, copper, zinc and cobalt
• M 4 comprises a metal selected from one or more of manganese, titanium and zirconium
• M 5 comprises a metal selected from one or more of aluminium, iron, cobalt, molybdenum, chromium, vanadium, scandium and yttrium.
• the active materials of Formula 1 are surprisingly capable of providing a specific charge capacity that is considerably higher than that predicted from conventional theoretical calculations.
• Especially preferred electrodes contain one or more active materials comprising:
• 0 ⁇ a ⁇ 1 preferably 0 ⁇ a ⁇ 0.5; further preferably 0 ⁇ a ⁇ 0.4; and highly preferably 0.1 ⁇ a ⁇ 0.4;
• v > 0, preferably 0 ⁇ v ⁇ 0.5; 0 ⁇ w ⁇ 0.5;
• c ⁇ 0.11 preferably c ⁇ 0.13 and highly preferably c ⁇ 0.15, preferably the upper limit for c is ⁇ 0.5
• Advantageous electrodes of the present invention contain one or more active materials comprising: io.25 io.25Mgo.25 no.25O1.75;
• the active materials used in the electrodes of the present invention may be prepared using any known method. However, a particularly convenient method involves effecting the net loss of Na 2 0 from one or more active cathode materials of Formula 2, where Formula 2 is defined as
• A' comprises either sodium or a mixed alkali metal in which sodium is the major constituent
• M 1 is nickel in oxidation state 2+
• M 2 comprises a metal in oxidation state 4+
• M 3 comprises a metal in oxidation state 2+
• M 4 comprises a metal in oxidation state 4+
• M 5 comprises a metal in oxidation state 3+
• a highly efficient process of producing compositions of Formula 1 comprises: charging an electrochemical cell containing one or more active cathode materials of Formula 2 beyond the conventional theoretical specific capacity as determined by the Ni 2+ /Ni 4+ redox couple; wherein Formula 2 is defined as:
• A' comprises either sodium or a mixed alkali metal in which sodium is the major constituent
• M 1 is nickel in oxidation state 2+
• M 2 comprises a metal in oxidation state 4+
• M 3 comprises a metal in oxidation state 2+
• M 4 comprises a metal in oxidation state 4+
• M 5 comprises a metal in oxidation state 3+
• the compounds of Formula 2 are disclosed in Applicant's patent applications GB1212263.6, GB1212268.5 and GB1212261.0 which documents are incorporated herein by reference.
• the process of overcharging involves charging the electrochemical cell containing the one or more active cathode materials to a specific capacity greater than 180mAh/g. Typically this means charging the Na-ion cell to at least 4.2V.
• the overcharging process is the first charge performed on the active materials although it may be possible to charge the active materials to their "normal" specific capacity first and follow this with a process in which the materials are overcharged.
• M 1 is nickel in oxidation state 4+
• M 2 comprises a metal in oxidation state 4+
• M 4 comprises a metal in oxidation state 4+
• the present invention therefore provides a method of increasing the specific charge capacity of an oxide-containing cathode composition for use in a Na-ion cell comprising:
• oxide-containing cathode composition in an electrochemical cell to cause the loss of oxygen from the oxide-containing cathode composition and thereby form an oxygen deficient oxide-containing cathode composition.
• the present invention provides an oxygen deficient oxide-containing cathode composition, for example made using the above method.
• the present invention provides an electrode comprising an oxygen deficient oxide-containing cathode composition, for example made using the above method.
• the mechanism by which oxygen is lost from the active cathode composition during the overcharging process operates most efficiently when the oxide-containing active cathode composition comprises a layered structure.
• Layered A x M0 2 materials are known to adopt several, very similar structural types, the most well-known of which have been categorised by Delmas et al. Physica B+C, 91 , (1980), 81 , as "03, P2 and P3".
• the letter refers to the way in which the oxygen ions are coordinated to the alkali ions, with the letter O denoting an octahedral coordination and the letter P denoting a prismatic coordination.
• the number refers to the number of M0 2 layers contained in the unit cell.
• the uncharged active cathode materials used in the electrodes of present invention it is preferred that they adopt a layered a-NaFe0 2 type structure (space group R-3m, no. 166), which has an 03 crystal structure. Following charging, these materials are thought to adopt 03, P2 or P3 or modified versions of these crystal structures, although it is also possible that other crystal structures may be adopted.
• layered active cathode materials for example of Formula 2
• they undergo a structural change which produces a reduction in the volume of the unit cell as compared with both the pristine precursor material, e.g. materials of Formula 2 before charging, and the precursor material after it has been charged to its conventional theoretical capacity, e.g. based on Ni 2+ to Ni 4+ .
• the unit cell volume reduction is consistent with the loss of alkali metal-ions and oxygen loss. This is discussed further below in the relation to the Specific Examples.
• Another characteristic of overcharged oxide-containing cathode compositions is that they appear to lose crystallinity (compared with to the uncharged material); this is shown by the FWHM of the 003 peak of the XRD pattern.
• a determination of when a material is said to be “overcharged” is made by observing the voltage curve for the particular material. At capacities less than or close to the conventional theoretical maximum charge capacity (i.e. the Ni 2+ /Ni 4+ redox couple) a first voltage feature is seen. However the curve continues to rise to a second voltage feature upon further or “over” charging. The materials are said to be “over-charged” from the beginning of this second voltage feature.
• the conventional theoretical maximum charge capacity i.e. the Ni 2+ /Ni 4+ redox couple
• the present invention provides a method of optimising the specific charge capacity of an oxide-containing cathode composition for use in a sodium-ion cell comprising charging the composition onto at least a portion of a voltage feature which is observed as a result of the oxide-containing cathode composition being charged above the conventional theoretical maximum charge capacity.
• the present invention also provides a method of optimising the specific charge capacity of an oxide-containing cathode composition in a sodium-ion cell comprising:
• discharging compounds of Formula 2 that have been "over-charged" results in producing materials of Formula 1 in which
• M 1 is nickel in oxidation state less than 4+
• At least one of M 2 and M 4 comprises a metal in oxidation state less than 4+
• c > 0.1 , preferably 0.1 ⁇ c ⁇ 0.5.
• the nickel is reduced from oxidation state 4+ to oxidation state 2+, some or all of the sodium-ions are reinserted into the lattice and the lost oxygen atoms are not replaced.
• the metals M 2 and/or M 4 do not contribute anything to the initial overcharging process, upon discharge of the overcharged material it is found that at least one of the metals M 2 and/or M 4 is also reduced to an oxidation state less than 4+. This allows some or all of the sodium ions that were removed during the first "over-charge" to be reinserted into the material, and therefore produces a material with a higher discharge capacity.
• the role of the Mn 4+ (or Ti 4+ ) in the uncharged materials of the present invention is to allow for the reduction (Na insertion) process during cell discharge. This is in direct contrast to the role of the manganese in US2007/0218361 which is to allow Na extraction by the Mn oxidation process Mn 3+ ⁇ Mn 4+ during the first charge process.
• the role of the M 3 and M 5 metals is to reduce the amount of nickel in the doped nickelate materials of Formula 1 , thereby allowing the "over charge” mechanism to take place as oxygen is released from the structure.
• the presence of the M 3 and M 5 metals also reduces the relative formula mass (formula weight) of these materials, thereby further improving the cost effectiveness of the electrode materials.
• oxide-containing cathode compositions When oxide-containing cathode compositions have undergone the over-charge/discharge process described, it is found that they may be cycled in the Na-ion cell between normal voltage limits for the Ni 2+ /Ni 4+ redox couple, typically this might be expected to be between 1 and 4V, and no further unconventional voltage plateaux are formed. Moreover, cycling the over-charged/discharged compositions at normal voltage limits maintains a higher specific capacity than would be expected from conventional theoretical calculations, i.e. the overcharged/discharged oxide-containing cathode compositions perform better than the pristine compounds when cycled using the same normal voltage limits.
• the present invention provides a method of using an oxide-containing cathode composition according to Formula 1 in a Na-ion cell comprising:
• the optimized oxide-containing cathode composition of the present invention may be prepared by a method that does not rely on overcharging a compound of Formula 2.
• the present invention includes an optimised oxide-containing cathode composition made by any route.
• the electrodes according to the present invention are suitable for use in many different applications, for example energy storage devices, rechargeable batteries, electrochemical devices and electrochromic devices.
• the electrodes according to the invention are used in conjunction with a counter electrode and one or more electrolyte materials.
• the electrolyte materials may be any conventional or known materials and may comprise either aqueous electrolyte(s) or nonaqueous electrolyte(s).
• the present invention also provides an energy storage device that utilises an electrode comprising the active materials described above, and particularly an energy storage device for use as a sodium-ion cell and/or a cell in which sodium is the major mobile ion; a cell in which sodium is the major alkali metal-ion; either of which may be used in a non-aqueous or an aqueous electrolyte system.
• Typical ways to achieve Na to Li-ion exchange include:
• FIGURE 1 (A) is a comparison of XRD profiles for a) the precursor starting material, NaNio.25Tio.25Mgo.25Mno.25O2, b) an electrode, originally containing NaNio.25Tio.25Mgo.25Mno.25O2, recovered from a cell after charging to 120mAh/g and c) an electrode, originally containing NaNio.25Tio.25Mgo.25Mno.25O2 recovered from a cell after charging to 230mAh/g;
• FIGURE 1 (B) shows the First Charge Process (Na-ion cell Voltage [V] versus Cathode Specific Charge Capacity [mAh/g]) for a Hard Carbon//NaNio .25 Tio .25 Mg 0.25 Mn 0.25 0 2 cell using an electrolyte of 0.5M sodium perchlorate in propylene carbonate (PC), charging to 230mAh/g;
• PC propylene carbonate
• FIGURE 2(A) shows the Charge-Discharge Voltage Profile for the first 4 cycles (Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for a Hard Carbon//NaNio.35Mn 0 .35Mg 0 .i5Tio.i502 cell, cycled between 1.5 to 4.2V;
• FIGURE 2(B) shows the Cycle Life Performance (Cathode Specific Capacity [mAh/g] versus Cycle Number) for a Hard Carbon// NaNio.35Mno.35Mgo.15Tio.15O2 cell, cycled between 1.5 to 4.2V;
• FIGURE 2(C) shows the Third Cycle Discharge Voltage Profile (Na-ion Cell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for a Hard Carbon//NaNio. 3 5Mn 0 . 3 5Mg 0 .i5Tio.i502 cell, cycled between 1.5 to 4.2V;
• FIGURE 2(D) shows the Third Cycle Differential Capacity Profiles (Differential Capacity [mAh/g/V]) versus Na-ion Cell voltage [V]) for a Hard Carbon//NaNio. 3 5Mn 0 . 3 5Mg 0 .i5Tio.i502 cell, cycled between 1.5 to 4.2V;
• FIGURE 3(A) shows the Charge-Discharge Voltage Profiles for the first 4 cycles (Na-ion cell Voltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for a Hard Carbon//NaNio.35Mn 0 .35Mg 0 .i5Tio.i502 cell, cycled between 1.5 to 4.4V;
• FIGURE 3(B) shows the Cycle Life Performance (Cathode Specific Capacity [mAh/g] versus Cycle Number) for a Hard Carbon// NaNio.35Mno.35Mgo.15Tio.15O2 cell, cycled between 1.5 to 4.4V;
• FIGURE 3(C) shows the Third Cycle Discharge Voltage Profile (Na-ion Cell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for a Hard Carbon//NaNio. 3 5Mn 0 . 3 5Mg 0 .i5Tio.i502 cell, cycled between 1.5 to 4.4V;
• FIGURE 3(D) shows the Third Cycle Differential Capacity Profiles (Differential Capacity [mAh/g/V]) versus Na-ion Cell voltage [V]) for a Hard Carbon//NaNio.35Mn 0 .35Mgo.i5Tio.i502 cell, cycled between 1.5 to 4.4V;
• FIGURE 4(A) shows the changes observed in the a and c cell parameters for NaNi25Tio.25Mgo.25Mrio.25O2 as pristine material, material charged to 120mAh/g and material charged to 230 mAh/g;
• FIGURE 4(B) shows the changes in unit cell volume for NaNi25Tio.25Mgo.25Mno.25O2 as pristine material, material charged to 120mAh/g and material charged to 230 mAh/g.
• any convenient process may be used to make the precursor materials (Formula 2) described above.
• the following general method may be used:
• Table 1 lists the starting materials and heating conditions used to prepare example precursor materials 1 to 12 of Formula 2.
• Example 1 The Preparation of Nin ? sTin ? sMg n ? sMnn ? sO 7 s
• Active precursor doped nickelate material NaNio.25Tio.25Mgo.25Mno.25O2 (compound xi in Table 1), prepared using the general method described above, was made into a hard carbon anode//NaNio .25 Tio .25 Mg 0.25 Mn 0.25 0 2 cathode cell using an electrolyte comprising 0.5M NaCI0 4 in propylene carbonate, see Figure 1 (A)a). Following a charge process to 230mAh/g, the cathode material was removed from the cell, washed several times in clean dimethyl carbonate and then dried at 70°C.
• Electrolyte 0.5 M NaCI0 4 in Propylene Carbonate.
• the cathode electrode disk was removed from the cell, washed several times in clean dimethyl carbonate to remove the electrolyte and then dried at 70°C.
• Example 2 The Preparation of Na a Nio sMno sMgo isTio isO?-r.
• the data shown in Figure 2A, 2B, 2C and 2D are derived from the constant current cycling data for a NaNio.35Mno.35Mgo.15Tio.15O2 (compound iii in Table 1) active precursor cathode material in a Na-ion cell where this cathode material is coupled with a Hard Carbon (Carbotron P/J) anode material.
• the electrolyte used is a 0.5 M solution of NaCI0 4 in propylene carbonate.
• the constant current data are collected at an approximate current density of 0.10 mA/cm 2 between voltage limits of 1.50 and 4.20 V.
• the Na-ion cell To fully charge the Na-ion cell it, is potentiostatically held at 4.2 V at the end of the constant current charging process. The testing is carried out at room temperature.
• sodium- ions are extracted from the cathode active material, and inserted into the Hard Carbon anode.
• sodium-ions are extracted from the Hard Carbon and re-inserted into the cathode active material.
• Figure 2A shows the first four charge-discharge cycles (Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for the Hard Carbon//NaNio. 3 5Mn 0 . 3 5Mg 0 .i5Tio.i502 cell.
• V Charging Cell Voltage
• mAh/g Cumulative Cathode Specific Capacity
• Figure 2(B) shows the cycle life performance (Cathode Specific Capacity [mAh/g] versus Cycle Number) for a Hard Carbon//NaNio. 3 5Mn 0 . 3 5Mg 0 .i5Tio.i502 cell.
• the cell shows good reversibility with the delivered cathode specific capacity reaching around 135 mAh/g after 4 cycles.
• Figure 2(C) shows the third cycle discharge voltage profile (Na-ion Cell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for the Hard Carbon//NaNio. 3 5Mn 0 . 3 5Mg 0 .i5Tio.i502 cell.
• the cathode specific capacity in this cycle corresponds to 130 mAh/g.
• Figure 2(D) shows the third cycle differential capacity profiles (Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for the Hard Carbon//NaNio. 3 5Mn 0 . 3 5Mg 0 .i5Tio.i502 cell. These symmetrical data demonstrate the excellent reversibility of the ion-insertion reactions in this Na-ion cell.
• the data shown in Figures 3(A), 3(B), 3(C) and 3(D) are derived from the constant current cycling data for a NaNio.35Mno.35Mgo.15Tio.15O2 (compound iii in Table 1)) active precursor material in a Na-ion cell where this cathode material is coupled with a Hard Carbon (Carbotron P/J) anode material.
• the electrolyte used is a 0.5 M solution of NaCI0 4 in propylene carbonate.
• the constant current data are collected at an approximate current density of 0.10 mA/cm 2 between voltage limits of 1.50 V and 4.40 V.
• FIG. 3(A) shows the first four charge-discharge cycles (Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for the Hard Carbon//NaNio .35 Mn 0 .35Mgo.i5Tio .
• Figure 3(B) shows the cycle life performance (Cathode Specific Capacity [mAh/g] versus Cycle Number) for the Hard Carbon//NaNio .35 Mn 0.35 Mg 0. i 5 Tio . i 5 0 2 cell.
• the cell shows good reversibility with the delivered cathode specific capacity reaching around 130 mAh/g after 4 cycles.
• Figure 3(C) shows the third cycle discharge voltage profile (Na-ion Cell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for the Hard Carbon//NaNio .35 Mn 0.35 Mg 0. i 5 Tio . i 5 0 2 cell.
• the cathode specific capacity in this cycle corresponds to 125 mAh/g.
• Figure 3(D) shows the third cycle differential capacity profiles (Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for the Hard Carbon//NaNio .35 Mn 0.35 Mg 0. i 5 Tio . i 5 0 2 cell. These symmetrical data demonstrate the excellent reversibility of the ion-insertion reactions in this Na-ion cell.
• the present invention has surprisingly demonstrated that when these sodium-based materials are overcharged, the 'labile' oxygen (which could contribute to thermal runaway) is caused to be removed from the structure; this yields the materials of the present invention which are highly thermodynamically stable and which are extremely effective and safe when used in reversible cathode materials.
• the XRD operating conditions used to analyse the precursor electrode materials are as follows:
• the XRD operating conditions used for ex-situ analysis of the electrodes are as follows: Slits sizes: 1 mm, 1 mm, 0.1 mm
• the target materials were tested either i) using a lithium metal anode test cell, or ii) using a Na-ion test cell using a hard carbon anode. It is also possible to test using a Li-ion cell with a graphite anode. Cells may be made using the following procedures:
• the positive electrode is prepared by solvent-casting a slurry of the active material, conductive carbon, binder and solvent.
• the conductive carbon used is Super P (Timcal).
• PVdF co-polymer e.g. Kynar Flex 2801 , Elf Atochem Inc.
• acetone is employed as the solvent.
• the slurry is then cast onto glass and a free-standing electrode film is formed as the solvent evaporates.
• the electrode is then dried further at about 80°C.
• the electrode film contains the following components, expressed in percent by weight: 80% active material, 8% Super P carbon, and 12% Kynar 2801 binder.
• an aluminium current collector may be used to contact the positive electrode.
• the electrolyte comprises one of the following: (i) a 1 M solution of LiPF 6 in ethylene carbonate (EC) and dimethyl carbonate (DMC) in a weight ratio of 1 : 1 ; (ii) a 1 M solution of LiPF 6 in ethylene carbonate (EC) and diethyl carbonate (DEC) in a weight ratio of 1 : 1 ; or (iii) a 1 M solution of LiPF 6 in propylene carbonate (PC)
• a glass fibre separator (Whatman, GF/A) or a porous polypropylene separator (e.g. Celgard 2400) wetted by the electrolyte is interposed between the positive and negative electrodes.
• a Na-ion electrochemical test cell containing the active material is constructed as follows: Generic Procedure to Make a Hard Carbon Na-ion Cell
• the positive electrode is prepared by solvent-casting a slurry of the active material, conductive carbon, binder and solvent.
• the conductive carbon used is Super P (Timcal).
• PVdF co-polymer e.g. Kynar Flex 2801 , Elf Atochem Inc.
• acetone is employed as the solvent.
• the slurry is then cast onto glass and a free-standing electrode film is formed as the solvent evaporates.
• the electrode is then dried further at about 80°C.
• the electrode film contains the following components, expressed in percent by weight: 80% active material, 8% Super P carbon, and 12% Kynar 2801 binder.
• an aluminium current collector may be used to contact the positive electrode.
• the negative electrode is prepared by solvent-casting a slurry of the hard carbon active material (Carbotron P/J, supplied by Kureha), conductive carbon, binder and solvent.
• the conductive carbon used is Super P (Timcal).
• PVdF co-polymer e.g. Kynar Flex 2801 , Elf Atochem Inc.
• acetone is employed as the solvent.
• the slurry is then cast onto glass and a free-standing electrode film is formed as the solvent evaporates.
• the electrode is then dried further at about 80°C.
• the electrode film contains the following components, expressed in percent by weight: 84% active material, 4% Super P carbon, and 12% Kynar 2801 binder.
• a copper current collector may be used to contact the negative electrode.
• the positive electrode is prepared by solvent-casting a slurry of the active material, conductive carbon, binder and solvent.
• the conductive carbon used is Super P (Timcal).
• PVdF co-polymer e.g. Kynar Flex 2801 , Elf Atochem Inc.
• acetone is employed as the solvent.
• the slurry is then cast onto glass and a free-standing electrode film is formed as the solvent evaporates.
• the electrode is then dried further at about 80°C.
• the electrode film contains the following components, expressed in percent by weight: 80% active material, 8% Super P carbon, and 12% Kynar 2801 binder.
• an aluminium current collector may be used to contact the positive electrode.
• the negative electrode is prepared by solvent-casting a slurry of the graphite active material (Crystalline Graphite, supplied by Conoco Inc.), conductive carbon, binder and solvent.
• the conductive carbon used is Super P (Timcal).
• PVdF co-polymer e.g. Kynar Flex 2801 , Elf Atochem Inc.
• acetone is employed as the solvent.
• the slurry is then cast onto glass and a free-standing electrode film is formed as the solvent evaporates.
• the electrode is then dried further at about 80°C.
• the electrode film contains the following components, expressed in percent by weight: 92% active material, 2% Super P carbon, and 6% Kynar 2801 binder.
• a copper current collector may be used to contact the negative electrode.
• the cell is cycled at a given current density between pre-set voltage limits.
• a commercial battery cycler from Maccor Inc. (Tulsa, OK, USA) is used.
• On charge sodium (lithium)-ions are extracted from the cathode active material.
• During discharge sodium (lithium)-ions are re-inserted into the cathode active material.
• the c-parameter increases upon charging to 120 mAh/g, and this is due to an increase in repulsion between the electronegative oxygen-ions of adjacent layers, as the sodium-ions are removed.

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