Lithium positive electrode active material and method of preparation

Abstract

The present invention relates to a lithium positive electrode active material containing dopants, for use in high voltage lithium secondary batteries. In particular, the present invention relates to such a material containing a combination of dopants D1, selected from Cu, Mg, Zn and D2, selected from Nb, V, Mo, which results in a high capacity and increased cycle life performance due to significant reduction of Ni / Mn dissolution in LNMO.

Description

[0001] LITHIUM POSITIVE ELECTRODE ACTIVE MATERIAL AND METHOD OF PREPARATION

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a lithium positive electrode active material for use in high voltage lithium secondary batteries. In particular, the present invention relates to such a material with a high capacity and increased life cycling. Moreover, the present invention relates to a process for the preparation of such a material and a battery cell including the same.

[0004] BACKGROUND OF THE INVENTION

[0005] Developing high energy density rechargeable battery materials have become a major research topic due to their broad applications in electric vehicles, portable electronics and grid-scale energy storage. Since their first commercialization in the early 1990s, Li-ion batteries (LIBs) present many advantages with respect to other commercial battery technologies. In particular, its higher specific energy and specific power make LIBs the best candidate for electric mobile transport application.

[0006] LNMO, or lithium nickel manganese oxide, is a lithium positive electrode active material that is gaining attention in the battery industry due to its promising electrochemical performance and relatively low cost compared to other high-energy-density cathode materials, such as NCA and LCO.

[0007] LNMO has a similar crystal structure to LMO, but with the addition of nickel, which increases its energy density and improves its thermal stability. LNMO also has a lower toxicity than other nickel-containing cathode materials, making it a more environmentally friendly option.

[0008] One of the main advantages of LNMO is its high-capacity retention and cycle stability, which means that it can maintain a high energy capacity over many charging and discharging cycles. This makes it a promising candidate for use in electric vehicle batteries, where long cycle life is critical.

[0009] W02020 / 127526 discloses a lithium positive electrode active material for a high voltage secondary battery, where the lithium positive electrode active materialcomprises at least 94 wt% spinel, said spinel having a net chemical composition of LixNiyMn2-yO4, where 0.95 < x < 1.05 and 0.43 < y < 0.47. The material described has a high capacity and a high voltage versus the Li / Li+reference. The patent discloses that a range of elements may be present either as impurities or as dopants; however, at the time of development, and considering that this prior art is from the same applicant as the present one, there were no further details regarding which properties could be improved, nor any qualitative or quantitative definition of the dopants, or how certain combinations of dopants could be beneficial.

[0010] US 2016 / 064733 discloses a lithium positive electrode active material, where a crystalline LiNbO3 or LiMg1-xNbxO3 phase improve capacity retention in Li-LNMO half cells. However, the capacity is very low and degradation rates are high.

[0011] US2021130190A1 discloses a lithium positive electrode active material, LNMO, where doping LNMO with Cu, Mg and Zn improve capacity retention in Li-LNMO half cells. However, from the data in the application it is noticed that the addition of Cu, Mg and Zn reduce capacity to 130mAh / g or below.

[0012] For battery materials, dissolution of transition metals from the material during cycling is a known issue contributing to loss of capacity, i.e. , fade, over time (Shkrob et al, J. Phys. Chem. C, 118, 24335 (2014); Solchenbach et al, J. Electrochem. Soc, 165, A3304 (2018); Jung et al, J. Electrochem. Soc., 166, A378 (2019)). Specifically, for LNMO, nickel and manganese dissolution has been identified as a contributing factor to degradation, where the dissolved nickel and manganese migrate to the anode, react with the solid electrolyte interphase and lead to further degradation at the anode surface that passivates active lithium in the cell and decreases capacity over time. Most of the prior art documents direct to the capacity degradation broadly, and some specifically to the Li dissolution. From our best knowledge of the state of the art and also out own previous developments, the addition of dopants has been investigated, but not addressing the specific solution of the nickel and manganese dissolution by the specific combination of dopants that enhances the effect of each other in specific low dosages.

[0013] In summary, despite the solutions mentioned in the state of the art, it is desirable to provide a cathode active material having improved performance over multiple chargeand discharge cycles, specifically addressing the issue with transition metals dissolution.

[0014] BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1. SEM image of comparative example;

[0016] Figure 2. SEM image of the material object of the invention;

[0017] Figure 3. Comparison of capacity and Mn dissolution;

[0018] Figure 4. Correlation between dissolution of Ni and Mn;

[0019] Figure 5. Graphic showing the Discharge capacity over cycle life;

[0020] Figure 6. Graphic showing the Coulombic efficiency over cycle life.

[0021] SUMMARY OF THE INVENTION

[0022] The present invention relates to a lithium positive electrode active material containing dopants, for use in high voltage lithium secondary batteries. In particular, the present invention relates to such a material with a high capacity, increased cycle life performance due to significant reduction of Ni / Mn dissolution from LNMO during cycling.

[0023] DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention is primarily directed towards the combination of dopants that significantly reduce the dissolution of Ni and Mn in LNMO during cycling, thereby enhancing performance, without negatively impacting the cell capacity.

[0025] As previously mentioned, it is well-known that the dissolution of Mn and Ni, followed by their migration to the anode, can lead to a decrease in cycle life.

[0026] Attempts have been done at single ion doping with several transition metals which have not yielded significant improvements in mitigating this issue. However, it has been discovered that the combination of specific metals, like Cu, Mg or Zn with Nb, V or Mo, preferably, Nb and Cu, effectively inhibits the dissolution of Ni and Mn. While the addition of those combinations of metals can limit the overall capacity of the cell, the present invention demonstrates that microdosing these elements maintains their beneficial effect of inhibiting Ni and Mn dissolution, while preserving high cell capacity. This innovative approach ensures that the cells with LNMOcathode active material exhibit enhanced cycle life and stability, making them more efficient and durable for long-term use. This is in particularly true for cells with LNMO as cathode active material and graphite as anode active material.

[0027] Thus, in an embodiment, the invention comprises a lithium positive electrode active material for a high voltage secondary battery, said lithium positive electrode active material comprising at least 94 wt% spinel structure, the material containing metals Li, Ni, Mn and two other transition metals, D1 and D2 in a molar ratio given by:

[0028] 3*n(Li) / (n(Li)+n(Ni)+n(Mn)+n(D1 )+n(D2))= X 3*n(Ni) / (n(Li)+n(Ni)+n(Mn)+n(D1)+n(D2)) = Y

[0029] 3*n(D1 ) / (n(Li)+n(Ni)+n(Mn)+n(D1 )+n(D2))= Z1 3*n(D2) / (n(Li)+n(Ni)+n(Mn)+n(D1 )+n(D2)) =Z2

[0030] In which n(Li), n(Ni), n(Mn), n(D1) and n(D2) are the molar amount of Li, Ni, Mn, D1 and D2, respectively,

[0031] 0.95<X<1.05,

[0032] 0.4<Y<0.5,

[0033] 0<Z1<0.1 and

[0034] 0<Z2<0.1.

[0035] In which the dopants transition metal D1 is selected from Cu, Mg, Zn and D2 is selected from Nb, V, Mo.

[0036] In a preferred embodiment of the invention, D1 is Cu and D2 is Nb, present in a most preferred molar amount of

[0037] 0.001 <Z1 <0.005 and

[0038] 0.003<Z2<0.01.

[0039] The molar ratio between D1 and D2 being around 1:2.

[0040] The material could also be defined as comprising the formula:

[0041] LixN iyM ns-x-Y-zi -zzD 1 zi D2Z2O4-6

[0042] wherein in a preferred embodiment

[0043] -0.1 <5<0.1 ,

[0044] 0.95<X<1.05,0.4<Y<0.5,

[0045] 0.001 <Z1 <0.005,

[0046] 0.003<Z2<0.01

[0047] Without being bound by theory, it is believed that the combination of Cu and Nb in the sample stabilizes Mn and Ni in the spinel structure. However, higher amounts of Nb might form other Nb phases such as LiNbOs, which will lower the spinel phase purity and have a negative effect on the capacity.

[0048] For the present invention, based on previous developments in the field and the behavior of the dopants in the cathode material, we conclude that it belongs to the scope of the current findings to substitute Cu with Mg and Zn as all three elements are divalent and have similar ionic radius in an oxygen lattice such as the LNMO spinel.

[0049] In analogy, we believe that it belongs to the scope of the current findings to substitute Nb with V and Mo, as all three are able to be in oxidation states 4+ and 5+ and because they have similar large ionic radius in an oxygen lattice such as the LNMO spinel.

[0050] The surface of the particles of the lithium positive electrode active material can be enriched with the dopant D2 compared to the average amount of D2 in the sample. This is because the high oxidation state and large ionic radius of Nb, V and Mo are expected to make these elements more difficult to include in the spinel structure. Figure 5 shows the development of discharge capacity in multilayer pouch cell test of lithium positive electrode active material prepared according to LNMO (comparative example 1) and LNMO-CuNb-low dosis (invention example 5).

[0051] Figure 6 shows coulombic efficiency of multilayer pouch cell test of lithium positive electrode active material prepared according to Example 1 (LNMO) and Example 5 (LNMO-CuNb-low).

[0052] From the results shown in Figures 5 and 6, we can conclude that although both capacity and Coulombic efficiency are not higher in the first 100 cycles, they remain higher between 200 and 300 cycles and forward. Therefore, the material that is the object of the invention presents much higher and more stable numbers for bothparameters — capacity and Coulombic efficiency — in longer cycles, indicating a significantly improved life cycle.

[0053] Coulombic efficiency, also known as charge efficiency, is a critical parameter in evaluating the performance of battery materials. It is defined as the ratio of the total charge extracted from the battery during discharge to the total charge supplied to the battery during the charging process. Mathematically, Coulombic efficiency is expressed as a percentage and is calculated using the formula: Coulombic Efficiency (%) = (Discharge Capacity I Charge Capacity) x 100. High Coulombic efficiency indicates that the battery material has minimal side reactions and losses during the charge / discharge cycles, leading to improved energy retention and longer cycle life. “Spinel” means a crystal lattice where oxygen is arranged in a slightly distorted cubic close-packed lattice that may be slightly distorted and cations occupying interstitial octahedral and tetrahedral sites in the lattice. Oxygen and the octahedrally coordinated cations form a framework structure with a 3-dimensional channel system which occupy the tetrahedrally coordinated cations. The ratio between tetrahedrally coordinated and octahedrally coordinated cations is approximately 1:2, and the cation to oxygen ratio is approximately 3:4 for spinel type structures. Cations in the octahedral site can consist of a single element or a mixture of different elements. If a mixture of different types of octahedrally coordinated cations by themselves form a three-dimensional periodic lattice, then the spinel is called an ordered spinel. If the cations are more randomly distributed, then the spinel is called a disordered spinel. Examples of an ordered and a disordered spinel, as described in the P4332 and Fd-3m space groups respectively, are described in Adv. Mater. (2012) 24, pp 2109-2116. For the purposes of clarification, when referred to fade it means capacity fade, which is defined as the gradual loss of a battery's ability to hold charge over repeated charge / discharge cycles. It is a critical parameter in assessing the long-term performance and durability of battery materials. Capacity fade is typically quantified by measuring the decrease in discharge capacity over a specified number of cycles and is expressed as a percentage. Mathematically, it can be calculated using the formula: Capacity Fade (%) = [(Initial Capacity - Final Capacity) I Initial Capacity] x 100. High capacity fade indicates significant degradation of the battery materials, leading to reduced energy storage capability and shorter operational life.In another aspect of the invention, the method for preparation of the material object of the invention is also described in a limited scale in the experimental section, but taken as basis for enlarged scale, by following the synthesis method comprising the steps of:

[0054] a) providing a lithium positive electrode active material comprising at least 94wt% spinel having a chemical composition of LixNiyMns-x-yCU, wherein 0.95<x<1.05 and 0.4<y<0.5,

[0055] b) mixing the lithium positive electrode active material of step a) with dopant precursors containing the dopants D1 and D2,

[0056] c) heating the mixture of step b) to a temperature of between 400°C and 1000°C. The temperature of step c) is preferred between 650°C and 800°C.

[0057] It is also part of the scope of the invention to comprise a battery cell containing the lithium positive electrode active material object of the invention.

[0058] EXPERIMENTAL SECTION EXAMPLE 1: Comparative example (LNMO)

[0059] Mn02 (269.5 g corresponding to 3.1 mol Mn), basic Ni(OH)x(CO3)y (133 g corresponding to 0.9 mol Ni) and Li2COs (73,9 g corresponding to 2.0 mol Li) and 1 L of water were weighed and ball-milled (600 rpm, for 30 minutes, with reverse rotation) in a planetary ball mill, in order to form a slurry with a molar ratio of Li:Ni:Mn = 1.00:0.45:1.55, corresponding toX=1.00, Y=0.45, Z1=0 and Z2=0. The mixture was then dried at 120°C, for 12 hours. The powder was then mixed in a mortar for 15 minutes to obtain a precursor. 20 g of the precursor was heated in a 50 mL crucible for 3 hours at 900°C in air, followed by cooling at 1.5°C / min to room temperature. The product was broken down in a mortar for 15 minutes and passed through a 45-micron sieve, resulting in cathode active material consisting of LNMO. The phase purity characterized with X-ray diffraction using Rietveld refinement was 96.6 wt%. The LNMO cathode active material of Example 1 is shown in Figure 1. It is seen that the typical size of primary crystals is in the range of 0.5 pm to 5 pm with an average particle size between 1 pm and 2 pm.EXAMPLE 2:

[0060]

[0061] exam

[0062]

[0063] Preparation of doped lithium positive electrode active material can be made by heating a lithium positive electrode active material, i.e. LixNiyMns-x-yCU (LNMO), with a dopant precursor. In this example, Cu-doped LNMO (LNMO-Cu) is prepared with LNMO material described in Example 1 as undoped starting material and CUNO3*2.5H2O, as dopant precursor.

[0064] CU(NO3)2*2.5H2O is dissolved in water and added to 20 g LNMO material in a ratio between transition metals Ni:Mn:Cu of 0.45:1.54:0.01 in the doped lithium positive electrode active material, corresponding to Y=0.45, Z1=0.01 and Z2=0. The slurry is dried at 80°C and calcined at 750°C for 4h in air. The product is broken down in a mortar for 15 minutes and passed through a 45-micron sieve, resulting in cathode active material consisting of Cu doped LNMO (LNMO-Cu). The phase purity characterized with X-ray diffraction using Rietveld refinement is 97.4 wt%.

[0065] EXAMPLE 3:

[0066]

[0067] exam

[0068]

[0069] Prepared as Example 2 using NH4NbO(C2O4)2(H2O)2*H2O, instead of CU(NO3)2*2.5H2O, to obtain a Nb doped LNMO (LNMO-Nb) with a molar ratio between transition metals of Ni:Mn:Nb of 0.44:1.50:0.06, corresponding to Y=0.44, Z1=0 and Z2=0.06. The phase purity characterized with X-ray diffraction using Rietveld refinement is 96.2 wt%.

[0070] EXAMPLE 4 (LNMO-CuNb)

[0071] Prepared as Example 2 using both NH4NbO(C2O4)2(H2O)*H2O and CU(NO3)2*2.5H2O, instead of Cu(NO3)2*2.5H2O, to obtain a CuNb doped LNMO (LNMO-CuNb) with a molar ratio between transition metals of Ni:Mn:Cu:Nb of 0.43:1.48:0.03:0.06, corresponding to Y=0.43, Z1=0.03 and Z2=0.06. The phase purity characterized with X-ray diffraction using Rietveld refinement is 95.4 wt%. EXAMPLE 5 (LNMO-CuNb-low)

[0072] Prepared as Example 2 using both NH4NbO(C2O4)2(H2O)*H2O and CU(NO3)2*2.5H2O, instead of Cu(NO3)2*2.5H2O, to obtain a CuNb doped LNMO (LNMO-CuNb-low) with a molar ratio between transition metals of Ni:Mn:Cu:Nb of 0.45:1.54:0.003:0.006, corresponding to Y=0.45, Z1 =0.003 and Z2=0.006. Thephase purity characterized with X-ray diffraction using Rietveld refinement is 98.7 wt%.

[0073] The LNMO cathode active material of Example 5 is shown in Figure 2. It is seen that both morphology and primary particle sizes are similar to the Comparative Example 1 shown in Figure 1. It is seen that the typical size of primary crystals is in the range of 0.5 pm to 5 pm with an average particle size between 1 pm and 2 pm.

[0074] EXAMPLE 6 (LNMO-CuNb-low)

[0075] MnO2 (465.1 g corresponding to 5.35 mol Mn), basic Ni(OH)x(CO3)y (217.6 g corresponding to 1.55 mol Ni), Li2COs (126.57 g corresponding to 3.41 mol Li), Nb2Os (2.75 g corresponding to 0.02 mol Nb), Cu2(OH)2CO3 (1.15 g corresponding to 0.01 mol Cu) and 1.7 L of water were weighed and ball-milled (600 rpm, for 30 minutes, with reverse rotation) in a planetary ball mill, in order to form a slurry with a molar ratio of Ni:Mn:Cu:Nb = 0.45:1.54:0.003:0.006, corresponding to Y=0.45, Z1 =0.003 and Z2=0.006. The mixture was then dried at 120°C, for 12 hours. The powder was then mixed in a mortar for 15 minutes to obtain a precursor. 100 g of the precursor was heated in a 250 mL crucible for 3 hours at 900°C in air, followed by cooling at 1.5°C / min to room temperature. The product was broken down in a mortar for 15 minutes and passed through a 45-micron sieve, resulting in cathode active material consisting of modified LNMO. The phase purity characterized with X-ray diffraction using Rietveld refinement was 97.5 wt%. SEM images show that morphology and particle size is similar to the LNMO cathode active material of Example 5 shown in Figure 2.

[0076] EXAMPLE 7 (LNMO-CuNb-low)

[0077] Mn02 (269.5 g corresponding to 3.1 mol Mn), basic Ni(OH)x(CO3)y (133 g corresponding to 0.9 mol Ni) and Li2COs (73,9 g corresponding to 2.0 mol Li) and 1 L of water were weighed and ball-milled (600 rpm, for 30 minutes, with reverse rotation) in a planetary ball mill, in order to form a slurry with a molar ratio of Li:Ni:Mn = 1.00:0.45:1.55, corresponding toX=1.00, Y=0.45, Z1=0 and Z2=0. The mixture was then dried at 120°C, for 12 hours. The powder was then mixed in a mortar for 15 minutes to obtain a precursor. To 100g of precursor were added Cu(NO3)2*2.5H2O and NH4NbO(C2O4)2(H2O)2*H2O in 100 mL of water. The sample was ball-milled inorder to form a slurry with a molar ratio of Ni:Mn:Cu:Nb = 0.45:1.54:0.003:0.006, corresponding to Y=0.45, Z1 =0.003 and Z2=0.006. The mixture was then dried at 120°C, for 12 hours. The powder was then mixed in a mortar and heated in a 250 mL crucible for 3 hours at 900°C in air, followed by cooling at 1.5°C / min to room temperature. The product was broken down in a mortar for 15 minutes and passed through a 45-micron sieve, resulting in cathode active material consisting of modified LNMO. The phase purity characterized with X-ray diffraction using Rietveld refinement was 96.6 wt%. SEM images show that morphology and particle size is similar to the LNMO cathode active material of Example 5 shown in Figure 2.

[0078] EXAMPLE 8: Electrochemical evaluation in LNMO-Li coin cells

[0079] I. Material and methods

[0080] Electrochemical tests were conducted in 2032 type coin cells to obtain the capacity of each of the materials from Examples 1-5 and to determine the amount of Mn and Ni dissolved during cycling. These results are reported in Table 1. The coin cells were made using thin composite positive electrodes of lithium positive electrode active material according to the invention and metallic lithium negative electrodes (halfcells). The thin composite positive electrodes were prepared by thoroughly mixing 92 wt% of lithium positive electrode active material (prepared as described in Example 1 , 2, 3, 4, 5, 6 or 7), with 4 wt% C65 carbon black (Imerys) and 4 wt% PVdF binder (polyvinylidene difluoride, Arkema) in NMP (N-methyl-pyrrolidone) to form a slurry. The slurry was spread onto a carbon coated aluminium foil using a doctor blade with a 120 pm gap and dried for 2 hours at 80°C to form a film.

[0081] Electrodes with a diameter of 14 mm and a loading of approximately 12 mg of lithium positive electrode active material, were cut from the dried film, pressed in a hydraulic pellet press (diameter 20 mm; 3 tonnes) and subjected to 10 hours, drying at 120°C under vacuum.

[0082] Coin cells were assembled in argon-filled glove box (< 1 ppm 02 and H2O), using a Whatman QMA quartz fiber separator and 90 pL electrolyte containing 1 molar LiPF6 in EC:DEC (1:1 in weight). One 0.5 mm thick lithium disk was used as counter electrode and the pressure in the cells were regulated with a stainless-steel disk spacer and disk spring on the negative electrode side.Electrochemical lithium insertion and extraction was monitored with an automatic cycling data recording system (Maccor) operating in galvanostatic mode. A test was programmed to continuously charge and discharge the cell between 3.5 V and 5.0 V, with current settings according to the following cycles. The current is listed as C-rates, e.g. 0.2C, which is described below. Formation (charge / discharge): Cycle 1: 0.2C / 0.2C, Cycle 2: 0.5C / 0.5C, Cycle 3: 0.5C / 1C, Cycle 4: 0.5C / 0.1C (prepare for slow cycle). Capacity test (charge / discharge): Cycle 5: 0.1C / 0.1C, Rate test (charge / discharge): Cycle 6-8: 0.5C / 1C, Cycle 9-11: 0.5C / 5C, Cycle 12-14: 0.5C / 10C, Cycling (charge / discharge): Cycle 15: 0.1C / 0.1C, Cycle 16-64: 0.5C / 1C, Cycle 65: 0.1C / 0.1C.

[0083] C-rates were calculated based on the theoretical specific capacity of the material of 147 mAh / g so that, e.g., 0.2C corresponds to 29.4 mA / g and 10C corresponds to 1.47 A / g. Degradation per 100 cycles is measured from after the power test, i.e. from cycle 15 to cycle 65. Mathematically, it can be calculated using the formula: Capacity Fade per 100 cycles (%) = [(Capacity at cycle 15 - Capacity at cycle 65) I Capacity at cycle 15] x [100 / (65 - 15)] x 100.

[0084] The capacity is determined as the capacity of the 5thcycle measured at 0.1 C.

[0085] Mn and Ni dissolution from the cathode during cycling was measured by analysis of the Mn and Ni content on the Li anode after the test was completed. To do this, the cell is disassembled, and the Li anodes are removed and oxidized in air for seven days prior to any reaction with aqueous reagents. The Li samples are extracted for 10 minutes with ultrasound with 2 ml pure water (18.2 MQ), 2 ml 65% HNO3 (suprapure quality) and 0.25 ml 30% H2O2 (suprapure quality) in a clean sample vial.

[0086] 5.75 ml pure water (18.2 MQ) is added to the resulting sample solution. This procedure fully dissolves the Li anode disc.

[0087] The contents of Mn and Ni in the sample solutions are quantified by Inductively Coupled Optical Emission Spectrometry (ICP-OES) with calibration by standard additions after 10 times dilution of the sample solutions. Mn and Ni are routinely calibrated up to 2.5 pg / ml on an Agilent 720 ICP-OES instrument, which corresponds to contents of Mn and Ni up to 250 pg in the anode disc samples. The amounts of Mn and Ni measured in this way are normalized to the amount of lithium positive electrode active material that was used as cathode in the coin cell test. Mn and Nidissolution is therefore reported as a percentage of the Mn and Ni in the tested lithium positive electrode active material.

[0088] II. Results

[0089]

[0090] Table 1 : Capacity and dissolution of Mn and Ni measured in based on cycling of cells with LNMO lithium cathode active materials from Examples 1-5 in LNMO-Li coin cells as described above.

[0091] As seen from Table 1 , the addition of Cu or Nb alone is not significantly lowering the dissolution of Mn and Ni, as per data results of Examples 2 and 3. However, if the two are combined, the dissolution of Mn and Ni is significantly reduced.

[0092] As seen in the results of Example 4, the combination of these dopants may decrease the capacity of the material. Optimization of the amounts of Cu and Nb show that a low dose, as the one in Example 5, will maintain the positive effect of lowering Mn and Ni dissolution, while at the same time maintaining a high capacity.

[0093] This conclusion is also shown in Figure 3, in which the comparison of capacity and Mn dissolution is plotted to identify the most promising samples. It is preferred to have a low Mn dissolution and a high capacity.

[0094] Figure 4 shows that the dissolved amount of Mn and Ni is correlating so that materials that show high dissolution of Mn is also showing high dissolution of Ni and vice versa.

[0095] EXAMPLE 9: Electrochemical evaluation in LNMO-graphite Multi-layer pouch cells

[0096] I. Material and methodsMultilayer pouch cells (MLP) are larger cells, used to produce commercial Li-ion batteries. Here, we used such cells to test lithium positive electrode active materials under technically relevant conditions, similar to commercial applications. Multilayer pouch cells were assembled from positive electrode made from material prepared according to Example 1 (LNMO) and Example 5 (LNMO-CuNb-low) and negative electrode (artificial graphite, XIAMEN TOB NEW ENERGY TECHNOLOGY Co., LTD). To make the positive electrodes, 92% active material, 4% C65 carbon black (Imerys), and 4% PVDF (Solvay) were mixed in NMP (N-methyl-pyrrolidone) to form a slurry. The slurry was coated on a thin aluminium foil with a thickness corresponding to an active material loading of approximately 18.5 mg / cm2 / side. Negative electrodes contained 95% artificial graphite coated on copper foil, with a loading of 8.3 mg / cm2 / side. Four positive electrodes and 5 negative electrodes were used for each cell, where they were separated by a 20 pm thin, porous separator made from polypropylene. Positive electrode dimensions were 80 mm by 60 mm and negative electrode dimensions were 82 mm by 62 mm. The total cell capacity after formation was approximately 0.75 Ah.

[0097] Cells were filled with electrolyte (1 molar LiPF6 in EC: EMC (3:7 in weight) + 1 wt% LiBOB) in an amount corresponding to 120% of the porosity in the cell (3.2-3.4 ml per cell, depending on exact electrode weight and porosity).

[0098] After electrolyte filling, cell formation was performed as follows: Charge to 4.8V with 0.1 C, then discharge to 4.0V with 0.33C, then one charge / discharge cycle with 0.33C. C-rates were calculated according to the amount of LNMO in the cell, and using a specific capacity of 140 mAh / g. After formation, the cell was degassed and continued cycling performed between 4.0 V and 4.8V with a charge current of 0.5C and discharge current of 1C. Cycling was continued to 500 cycles or until severe capacity loss. Formation and cycling were performed at 25°C.

[0099] II. Results

[0100] MLP cells were made from positive electrode material according to Example 1 (LNMO) and Example 5 (LNMO-CuNb-low)) and tested for extensive cycling.The capacity development of two such cells is presented in Figure 5, where capacity is shown on the y-axis relative to the first 0.5C / 1 C cycle. A common criterion for end of life for a Li-ion cell is when it reaches 80% of the original capacity. For the cell prepared from LNMO, this happens after 323 cycles, whereas the cell made from LNMO-CuNb-low still retains 82% capacity after 500 cycles. A further analysis shows that the cell made from LNMO exhibits an approximately linear capacity fade for the first 200 cycles, whereafter a more rapid decay initiate. The cell made form LNMO-CuNb-low, does not experience this form of rapid decay within the 500 cycles. Before the rapid decay, the two cells also exhibit a different rate of loss, i.e. calculated between cycle 100 and cycle 200. LNMO-CuNb-low loses 3.5 % capacity, whereas LNMO loses 4.5 % capacity.

[0101] The coulombic efficiency (ratio between charge and discharge capacity) of the two cells is shown in Figure 6. Coulombic efficiency is a measure of irreversible processes in the battery and generally a coulombic efficiency very close to 1 is required for long cycle life. The rapid capacity fade of the cell made from LNMO is closely correlated with a decaying coulombic efficiency, which is a clear measure that unwanted processes take place in the cell. For the LNMO-CuNb-low cell, coulombic efficiency is stable over the 500 cycles, allowing for extended cycle life.

[0102] This comparison of identically prepared cells, with the only difference being the positive electrode material, clearly shows in Figures 5 and 6 the benefit of the present invention in enhancing the cycle life of LNMO based Li-ion cells.

Claims

CLAIMS1. A lithium positive electrode active material for a high voltage secondary battery, said lithium positive electrode active material comprising at least 94 wt% spinel structure, the material containing metals Li, Ni, Mn and two other transition metals D1 and D2 in a molar ratio given by:3*n(Li) / (n(Li)+n(Ni)+n(Mn)+n(D1 )+n(D2))= X 3*n(Ni) / (n(Li)+n(Ni)+n(Mn)+n(D1)+n(D2)) = Y3*n(D1 ) / (n(Li)+n(Ni)+n(Mn)+n(D1 )+n(D2))= Z1 3*n(D2) / (n(Li)+n(Ni)+n(Mn)+n(D1 )+n(D2)) =Z2whereinn(Li), n(Ni), n(Mn), n(D1) and n(D2) are the molar amount of Li, Ni, Mn, D1 and D2, respectively,0.95<X<1.05,0.4<Y<0.5,0<Z1<0.1 and0<Z2<0.1whereinD1 is selected from Cu, Mg, ZnD2 is selected from Nb, V, Mo2. Lithium positive electrode active material, according to claim 1, wherein D1 is Cu.

3. Lithium positive electrode active material, according to claims 1 or 2, wherein D2 is Nb.

4. Lithium positive electrode active material, according to any one of the preceding claims, wherein Z1 >0.001.

5. Lithium positive electrode active material, according to any one of the preceding claims, wherein Z1 <0.005.

6. Lithium positive electrode active material, according to any one of the preceding claims, wherein Z2>0.003.

7. Lithium positive electrode active material, according to any one of the preceding claims, wherein Z2<0.01.

8. Lithium positive electrode active material, according to any of the claims 2 to 7, wherein the molar ratio between Cu and Nb being around 1 :2.

9. Lithium positive electrode active material, according to any one of the preceding claims, wherein the material comprises the formula:LixN iyM ns-x-Y-zi -zzD 1 zi D2Z2O4-6wherein-0.1 <5<0.1 ,0.95<X<1.05,0.4<Y<0.5,0.001 <Z1 <0.005,0.003<Z2<0.01.

10. A lithium positive electrode active material, according to any one of the preceding claims, wherein the surface of the particles of the lithium positive electrode active material is enriched with the dopant D2 compared to the average amount of D2 in the sample.

11. A lithium positive electrode active material according to claim 1 , wherein the size of primary crystals is in the range between 0.5 pm and 5 pm with an average particle size between 1 pm and 2 pm.

12. A lithium positive electrode active material according to claim 1, wherein it has a capacity above 130 mAh / g, preferably above 135 mAh / g.

13. A battery cell containing the lithium positive electrode active material as defined in any one of claims 1 to 12.

14. A process for preparing a lithium positive electrode active material as described in the claims 1 to 12, wherein the process is a synthesis method comprising the steps of:a) providing a lithium positive electrode active material comprising at least 94wt% spinel having a chemical composition of LixNiyMns-x-yCU, wherein 0.95<x<1.05 and 0.4<y<0.5,b) mixing the lithium positive electrode active material of step a) with dopant precursors containing the dopants D1 and D2,c) heating the mixture of step b) to a temperature of between 400°C and 1000°C.

15. A process according to claim 14, wherein the temperature of step c) is between 650°C and 800°C.

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